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Corticotropin-releasing factor projections from limbic forebrain and paraventricular nucleus of the hypothalamus to the region of the ventral tegmental area
Abstract
Corticotropin-releasing factor (CRF) is a peptide neurotransmitter with high numbers of cell bodies found in limbic regions of the rat brain including the oval nucleus of the bed nucleus of the stria terminalis (BNSTov) and central nucleus of the amygdala (CeA) as well as in the paraventricular nucleus of the hypothalamus (PVN). CRF systems are activated in response to acute stressors and mediate a wide variety of physiological and behavioral responses to acute stress including aversive responses and responses that support appetitive behaviors. CRF is released in the ventral tegmental area (VTA), the cell body region of the mesocorticolimbic dopaminergic neurons, in response to acute stress and plays a role in stress-activation of appetitive behavior [Wang B, Shaham Y, Zitzman D, Azari S, Wise RA, You ZB (2005) Cocaine experience establishes control of midbrain glutamate and dopamine by corticotropin-releasing factor: a role in stress-induced relapse to drug seeking. J Neurosci 25:5389-5396]. However, although it is known that the VTA region contains significant levels of CRF-immunoreactive fibers [Swanson LW, Sawchenko PE, Rivier J, Vale WW (1983) Organization of ovine corticotropin-releasing factor immunoreactive cells and fibers in the rat brain: an immunohistochemical study. Neuroendocrinology 36:165-186], the source of CRF input to the region has not been identified. We used infusions of a fluorescent retrograde tracer, fluorogold, into the VTA region, combined with fluorescent immunocytochemistry for CRF to identify sources of this input. Double-labeled cells were found in BNSTov, CeA and PVN. The percent of fluorogold-labeled cells in each region that were CRF-positive was 30.8, 28.0 and 16.7% respectively. These data point to diffusely distributed sources of CRF-containing fibers in the VTA.
... A series of studies by Winder and colleagues have demonstrated that beta adrenergic receptors promote excitatory regulation of key BNST output pathways involved in cocaine seeking via a mechanism that likely requires CRF release from a local population of neurons intrinsic to the BNST and BNST CRF-R1 receptor activation [84,85]. These pathways include CRF-positive neurons that innervate the VTA [85][86][87], where CRF receptor activation is required for stressor-induced cocaine seeking ( [88,89]; see below). Indeed, bath application of the non-selective beta-adrenergic receptor agonist, isoproterenol, promotes excitatory synaptic regulation of retro-labeled VTA-projecting CRFpositive neurons via CRF-R1-dependent glutamate release in the BNST [85]. ...
... The BNST-VTA projection is comprised of both GABAergic and glutamatergic neurons [90]. However, it has been reported that CRF-positive neurons that project from the BNST to VTA [83,87] are primarily GABAergic [8]. To confirm that beta-2 adrenergic receptor regulation of a projection from the ventral BNST that releases CRF into the VTA mediates stressor-induced cocaine seeking, we deployed a pharmacological disconnection approach in which we administered the beta-2 adrenergic receptor antagonist, ICI-118,551, into the BNST in one hemisphere and the CRF-R1 antagonist, antalarmin, into the contralateral VTA. ...
... Both CRF-R1 and CRF-R2 receptors [21,111,112] as well as the CRF binding protein [113] are expressed in the region. The VTA receives CRF-releasing inputs from several brain regions implicated in stress-related hormonal and behavioral responses, most notably the CeA, the paraventricular nucleus of the hypothalamus, and BNST [87]. There is also evidence for local VTA CRF release [14]. ...
The neuropeptide, corticotropin releasing factor (CRF), has been an enigmatic target for the development of medications aimed at treating stress-related disorders. Despite a large body of evidence from preclinical studies in rodents demonstrating that CRF receptor antagonists prevent stressor-induced drug seeking, medications targeting the CRF-R1 have failed in clinical trials. Here, we provide an overview of the abundant findings from preclinical rodent studies suggesting that CRF signaling is involved in stressor-induced relapse. The scientific literature that has defined the receptors, mechanisms and neurocircuits through which CRF contributes to stressor-induced reinstatement of drug seeking following self-administration and conditioned place preference in rodents is reviewed. Evidence that CRF signaling is recruited with repeated drug use in a manner that heightens susceptibility to stressor-induced drug seeking in rodents is presented. Factors that may determine the influence of CRF signaling in substance use disorders, including developmental windows, biological sex, and genetics are examined. Finally, we discuss the translational failure of medications targeting CRF signaling as interventions for substance use disorders and other stress-related conditions. We conclude that new perspectives and research directions are needed to unravel the mysterious role of CRF in substance use disorders.
... CRF receptor activation appears to occur downstream of noradrenergic stimulation (Brown et al., 2009), and activation of these CRF receptors has been shown to be integral in stress-induced drug seeking (Blacktop et al., 2011;Chen et al., 2014;Vranjkovic et al., 2014;Wang et al., 2005 but see Wang, You, Rice and Wise, 2007). The CeA has CRF projections to both the BNST (Erb et al., 2001) and the VTA (Rodaros et al., 2007), and upregulated CRF receptor expression and CRF release have been observed within the amygdala during cocaine withdrawal (Richter and Weiss, 1999;Zorrilla et al., 2001). The BNST, in turn, contains both CRF interneurons (Erb et al., 2001) and makes CRF projections to the VTA (Rodaros et al., 2007) that have been implicated in stress-induced drug seeking. ...
... The CeA has CRF projections to both the BNST (Erb et al., 2001) and the VTA (Rodaros et al., 2007), and upregulated CRF receptor expression and CRF release have been observed within the amygdala during cocaine withdrawal (Richter and Weiss, 1999;Zorrilla et al., 2001). The BNST, in turn, contains both CRF interneurons (Erb et al., 2001) and makes CRF projections to the VTA (Rodaros et al., 2007) that have been implicated in stress-induced drug seeking. The paraventricular nucleus of the hypothalamus (PVN) also makes CRF-containing projections to the VTA (Rodaros et al., 2007). ...
... The BNST, in turn, contains both CRF interneurons (Erb et al., 2001) and makes CRF projections to the VTA (Rodaros et al., 2007) that have been implicated in stress-induced drug seeking. The paraventricular nucleus of the hypothalamus (PVN) also makes CRF-containing projections to the VTA (Rodaros et al., 2007). VTA dopaminergic release is regulated by CRF (Wanat et al., 2013;Wang et al., 2005), and CRF receptor-regulated dopaminergic projections to the prelimbic cortex are necessary for stress-induced reinstatement of cocaine seeking in rodents. ...
Stress is a frequent precipitant of relapse to drug use. Pharmacotherapies targeting a diverse array of neural systems have been assayed for efficacy in attenuating stress-induced drug-seeking in both rodents and in humans, but none have shown enough evidence of utility to warrant routine use in the clinic. We posit that a critical barrier in effective translation is inattention to sex as a biological variable at all phases of the research process. In this review, we detail the neurobiological systems implicated in stress-induced relapse to cocaine, opioids, methamphetamine, and cannabis, as well as the pharmacotherapies that have been used to target these systems in rodent models, the human laboratory, and in clinical trials. In each of these areas we additionally describe the potential influences of biological sex on outcomes, and how inattention to fundamental sex differences can lead to biases during drug development that contribute to the limited success of large clinical trials. Based on these observations, we determine that of the pharmacotherapies discussed only α2-adrenergic receptor agonists and oxytocin have a body of research with sufficient consideration of biological sex to warrant further clinical evaluation. Pharmacotherapies that target β-adrenergic receptors, other neuroactive peptides, the hypothalamic-pituitary-adrenal axis, neurosteroids, and the endogenous opioid and cannabinoid systems require further assessment in females at the preclinical and human laboratory levels before progression to clinical trials can be recommended.
... Neural circuitry and behavioral evidence suggest CRF+ aBNST neurons are also involved in stress effects on motivation behaviors. CRF+ aBNST neurons project to [27][28][29] and inhibit [17,30] ventral tegmental area (VTA) and nucleus accumbens (NAc) shell. Stress-induced neuroplasticity increases the inhibitory actions of CRF in VTA and impairs reward responsivity [31][32][33]. ...
... Optogenetically activating VTA-projecting GABAergic BNST neurons is anxiolytic and rewarding [38]. Here, we used cell-specific chemogenetic activation of CRF+ aBNST neurons, which release GABA [63,64] in the VTA [17,27,29,30] and NAc [17]. We hypothesize that chemogenetics activated the inhibitory BNST CRF -VTA circuit, reducing effortful motivation behaviors. ...
Corticotropin-releasing factor (CRF) in the anterior bed nucleus of the stria terminalis (aBNST) is associated with chronic stress and avoidance behavior. However, CRF + BNST neurons project to reward- and motivation-related brain regions, suggesting a potential role in motivated behavior. We used chemogenetics to selectively activate CRF+ aBNST neurons in male and female CRF-ires-Cre mice during an effort-related choice task and a concurrent choice task. In both tasks, mice were given the option either to exert effort for high value rewards or to choose freely available low value rewards. Acute chemogenetic activation of CRF+ aBNST neurons reduced barrier climbing for a high value reward in the effort-related choice task in both males and females. Furthermore, acute chemogenetic activation of CRF+ aBNST neurons also reduced effortful lever pressing in high-performing males in the concurrent choice task. These data suggest a novel role for CRF+ aBNST neurons in effort-based decision and motivation behaviors.
... Potential sources of CRF to the various DA subregions are therefore diverse, but have not been well studied (reviewed in, Kelly and Fudge, 2018). A large known source of CRF to the rodent and primate PBP and A8 subregions arises from the central extended amygdala (Rodaros et al., 2007;Dabrowska et al., 2016;Fudge et al., 2017). ...
... In rodents, the VTA receives CRF-containing afferents from lateral bed nucleus of stria terminalis (BSTL), the central nucleus of the amygdala (CeN), and the paraventricular nucleus (PVN) (Rodaros et al., 2007;Dabrowska et al., 2016). However, the CRF innervation of other DA subregions has generally been ignored. ...
Dopamine (DA) is involved in stress and stress-related illnesses, including many psychiatric disorders. Corticotropin-releasing factor (CRF) plays a role in stress responses and targets the ventral midbrain DA system. This system is comprised of DA and non-DA cells and is divided into specific subregions. Although CRF inputs to the midline A10 nuclei of the DA system are well studied in rodents, in monkeys, CRF-containing terminals are also highly enriched in the expanded A10 parabrachial pigmented nucleus (PBP) and in the A8 retrorubral field subregion. In primates, the central extended amygdala, a rich source of CRF afferents across species, preferentially targets the PBP and A8 fields. We thus sought to characterize CRF terminals on DA (tyrosine hydroxylase, TH+) and non-DA (TH-) cell types in the PBP and A8 regions at the ultrastructural level using immuno-reactive electron microscopy (EM) for TH and CRF in male and female macaques. CRF labeling was present mostly in axon terminals, which mainly contacted non-DA dendrites in both subregions. Most CRF-positive terminals had inhibitory (symmetric) profiles. In the A8, CRF symmetric (inhibitory) contacts onto non-DA neurons were significantly greater than asymmetric (excitatory) profiles; this pattern was also seen in the PBP, but did not reach statistical significance. No sex differences were found. Hormonal assays suggested that our animals were at similar developmental stages and experienced similar stress levels. Together our findings suggest that at baseline, CRF terminals in the primate PBP and A8 largely regulate DA indirectly through non-DA neurons.
... Key brain regions involved in CRF-mediated stress responses are the paraventricular nucleus of the hypothalamus (PVN), CeA and BNST (c.f., Ronan & Summers, 2011). These regions send direct CRF projections to dopaminergic cells of the ventral tegmental area (VTA; Rodaros, Caruana, Amir, & Stewart, 2007) where CRF has both electrophysiological and behavioral effects (Lodge & Grace, 2005). CRF also plays a key role in nucleus accumbens (NAc) reward-related behavior (Marcinkiewcz et al., 2009;Pecina, Schulkin, & Berridge, 2006). ...
... Enhanced CRF activity in the PVN could also increase susceptibility to addiction. The PVN sends CRF projections to many brain regions including the VTA (Rodaros et al., 2007), where CRF infusion leads to reinstatement of cocaine self-administration (Wang et al., 2005;Wang, You, Rice, & Wise, 2007). Increased CRF mRNA in the PVN is correlated with increased anxiety and neuroendocrine responses to withdrawal from drugs of abuse (c.f., Cleck & Blendy, 2008) and has been directly implicated in stress-induced reinstatement of self-administration for drugs of abuse (Koob & Kreek, 2007). ...
Early life stress (ELS) is a risk factor for developing a host of psychiatric disorders. Adolescence is a particularly vulnerable period for the onset of these disorders and substance use disorders (SUDs). Here we discuss ELS and its effects in adolescence, especially SUDs, and their correlates with molecular changes to signaling systems in reward and stress neurocircuits. Using a maternal separation (MS) model of neonatal ELS, we studied a range of behaviors that comprise a “drug-seeking” phenotype. We then investigated potential mechanisms underlying the development of this phenotype. Corticotropin releasing factor (CRF) and serotonin (5-HT) are widely believed to be involved in “stress-induced” disorders, including addiction. Here, we show that ELS leads to the development of a drug-seeking phenotype indicative of increased susceptibility to addiction and concomitant sex-dependent upregulation of CRF and 5-HT system components throughout extended brain reward/stress neurocircuits.
... BNST projections to the ventral tegmental area (VTA) are critical for stressor-triggered drug seeking. These projections include both GABAergic and glutamatergic neurons (Kaufling et al., 2017) although the subpopulation of these neurons that express CRF (Rodaros et al., 2007;Vranjkovic et al., 2014) is primarily GABAergic (Dabrowska et al., 2013). Beta-adrenergic receptor agonist application to brain slices containing the BNST promotes excitatory synaptic regulation of retro-labeled VTA-projecting CRF-positive neurons via CRF-R1-dependent glutamate release (Silberman et al., 2013). ...
... Using a pharmacological disconnection approach in which we administered the beta-2 adrenergic receptor antagonist, ICI-118,551, into the BNST in one hemisphere and the CRF-R1 antagonist, antalarmin, into the contralateral VTA, we have demonstrated that the beta-2 receptor regulated CRF-releasing pathway from the BNST to the VTA is required for shock-induced reinstatement of cocaine seeking following self-administration in rats . It is important to note, however, that other brain regions send CRF projections to the VTA (Rodaros et al., 2007) and may be involved in stressor-triggered drug seeking. ...
In individuals with substance use disorders, stress is a critical determinant of relapse susceptibility. In some cases, stressors directly trigger cocaine use. In others, stressors interact with other stimuli to promote drug seeking, thereby setting the stage for relapse. Here, we review the mechanisms and neurocircuitry that mediate stress‐triggered and stress‐potentiated cocaine seeking. Stressors trigger cocaine seeking by activating noradrenergic projections originating in the lateral tegmentum that innervate the bed nucleus of the stria terminalis to produce beta adrenergic receptor‐dependent regulation of neurons that release corticotropin releasing factor (CRF) into the ventral tegmental area (VTA). CRF promotes the activation of VTA dopamine neurons that innervate the prelimbic prefrontal cortex resulting in D1 receptor‐dependent excitation of a pathway to the nucleus accumbens core that mediates cocaine seeking. The stage‐setting effects of stress require glucocorticoids, which exert rapid non‐canonical effects at several sites within the mesocorticolimbic system. In the nucleus accumbens, corticosterone attenuates dopamine clearance via the organic cation transporter 3 to promote dopamine signaling. In the prelimbic cortex, corticosterone mobilizes the endocannabinoid, 2‐arachidonoylglycerol (2‐AG), which produces CB1 receptor‐dependent reductions in inhibitory transmission, thereby increasing excitability of neurons which comprise output pathways responsible for cocaine seeking. Factors that influence the role of stress in cocaine seeking, including prior history of drug use, biological sex, chronic stress/co‐morbid stress‐related disorders, adolescence, social variables, and genetics are discussed. Better understanding when and how stress contributes to drug seeking should guide the development of more effective interventions, particularly for those whose drug use is stress related.
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... We then determined the brain areas that were activated (or suppressed) after administration of THIP (6 mg/kg), in order to understand the possible neuronal circuitry underlying the aversive behavioral effect and elevated corticosterone levels. Neuronal activation was measured by detection of c-Fos expressing nuclei in various brain areas enriched with δ-GABA A receptors and CRF (Pirker et al., 2000;Rodaros et al., 2007;Hörtnagl et al., 2013). The effects of THIP on c-Fos expression at 2 h after the injection are shown in Table 2. THIP altered neuronal activity in a brain region-specific manner ( Table 2; Kruskal-Wallis, p < 0.005). ...
... The ovBNST harbors one of the highest densities of CRF-expressing neurons within the BNST complex, receiving many CRF inputs from the central amygdala (Sakanaka et al., 1986;Beckerman et al., 2013). Furthermore, the ovBNST is among the brain regions sending CRF-positive projections to the VTA GABA neurons (Rodaros et al., 2007). Indeed, additional immunohistochemical analysis of the ovBNST revealed that after THIP treatment 64% of c-Fos positive cells were CRF-expressing neurons. ...
THIP (gaboxadol), a superagonist of the δ subunit-containing extrasynaptic GABAA receptors, produces persistent neuroplasticity in dopamine (DA) neurons of the ventral tegmental area (VTA), similarly to rewarding drugs of abuse. However, unlike them THIP lacks abuse potential and induces conditioned place aversion in mice. The mechanism underlying the aversive effects of THIP remains elusive. Here, we show that mild aversive effects of THIP were detected 2 h after administration likely reflecting an anxiety-like state with increased corticosterone release and with central recruitment of corticotropin-releasing factor corticotropin-releasing factor receptor 1 (CRF1) receptors. A detailed immunohistochemical c-Fos expression mapping for THIP-activated brain areas revealed a correlation between the activation of CRF-expressing neurons in the oval nucleus of the bed nuclei of stria terminalis and THIP-induced aversive effects. In addition, the neuroplasticity of mesolimbic DA system (24 h after administration) and conditioned place aversion by THIP after four daily acute sessions were dependent on extrasynaptic GABAA receptors (abolished in δ-GABAA receptor knockout mice) and activation of the CRF1 receptors (abolished in wildtype mice by a CRF1 receptor antagonist). A selective THIP-induced activation of CRF-expressing neurons in the oval part of the bed nucleus of stria terminalis may constitute a novel mechanism for inducing plasticity in a population of VTA DA neurons and aversive behavioral states.
... The amygdalonigral path is involved in both appetitive and aversive learning and behaviors (Price and Amaral, 1981;Gonzales and Chesselet, 1990;Zahm et al., 1999;Fudge et al., 2017;Steinberg et al., 2020). At least a subset of neurons in the amygdalonigral path co-contain corticotropin releasing factor (CRF) (Rodaros et al., 2007;Fudge et al., 2017;Steinberg et al., 2020). Importantly, the CeN projection to the ventral midbrain largely avoids the midline subnuclei of the A10 (midline VTA) in mice, rats, and monkeys (Deutch et al., 1988;Gonzales and Chesselet, 1990;Wallace et al., 1992;Fudge and Haber, 2000;Lee et al., 2005;Steinberg et al., 2020), terminating instead over the elongated parabrachial pigmented nucleus (PBP, or 'lateral VTA') and also the retrorubral field (A8) Fudge et al., 2017). ...
The central nucleus (CeN) of the amygdala is an important afferent to the DA system that mediates motivated learning. We previously found that CeN terminals in nonhuman primates primarily overlap the elongated lateral VTA (parabrachial pigmented nucleus, PBP, A10), and retrorubral field(A8) subregion. Here, we examined CeN afferent contacts on cell somata and proximal dendrites of DA and GABA neurons, and distal dendrites of each, using confocal and electron microscopy (EM) methods, respectively. At the soma/proximal dendrites, the proportion of TH+ and GAD1+ cells receiving at least one CeN afferent contact was surprisingly similar (TH = 0.55: GAD1=0.55 in PBP; TH = 0.56; GAD1 =0.51 in A8), with the vast majority of contacted TH+ and GAD1+ soma/proximal dendrites received 1-2 contacts. Similar numbers of tracer-labeled terminals also contacted TH-positive and GAD1-positive small dendrites and/or spines (39% of all contacted dendrites were either TH- or GAD1-labeled). Overall, axon terminals had more symmetric (putative inhibitory) axonal contacts with no difference in the relative distribution in the PBP versus A8, or onto TH+ versus GAD1+ dendrites/spines in either region. The striking uniformity in the amygdalonigral projection across the PBP-A8 terminal field suggests that neither neurotransmitter phenotype nor midbrain location dictates likelihood of a terminal contact. We discuss how this afferent uniformity can play out in recently discovered differences in DA:GABA cell densities between the PBP and A8, and affect specific outputs.
... CRF signaling via CRFR1 in the AMG, septum, and PFC has been implicated in negative affective states such as anxiety and aversion. CRF neurons in the basolateral nucleus and mPFC project axons to the NAc [66], whereas CRF neurons in the PVN and CeA send projections to the VTA [67]. CRFR1 is localized on DA neurons in the VTA [68] and DA terminals in the NAc [69]. ...
Alterations in the various neuropeptide systems in the mesocorticolimbic circuitry have been implicated in negative effects associated with drug withdrawal. The corticotropin-releasing factor (CRF) and α-melanocyte-stimulating hormone are two peptides that may be involved. This study investigated the regulatory effects of chronic nicotine exposure and withdrawal on the mRNA levels of melanocortin receptors (MC3R, MC4R), CRF, and CRF receptors (CRFR1 and CRFR2) expressed in the mesocorticolimbic system. Rats were given drinking water with nicotine or without nicotine (control group) for 12 weeks, after which they continued receiving nicotine (chronic exposure) or were withdrawn from nicotine for 24 or 48 h. The animals were decapitated following behavioral testing for withdrawal signs. Quantitative real-time PCR analysis demonstrated that nicotine exposure (with or without withdrawal) increased levels of CRF and CRFR1 mRNA in the amygdala, CRF mRNA in the medial prefrontal cortex, and CRFR1 mRNA in the septum. Nicotine withdrawal also enhanced MC3R and MC4R mRNA levels in different brain regions, while chronic nicotine exposure was associated with increased MC4R mRNA levels in the nucleus accumbens. These results suggest that chronic nicotine exposure and withdrawal regulate CRF and melanocortin signaling in the mesocorticolimbic system, possibly contributing to negative affective state and nicotine addiction.
... In parallel work, we have demonstrated that the LH is an important substrate of chronic stress-induced motivational disturbances [20]. Together these studies suggest a more nuanced role for PVN CRH neurons in motivated behavior, potentially via their projections to brain regions critical for motivation such as the LH or ventral tegmental area (VTA) [21]. ...
Impaired motivational drive is a key feature of depression. Chronic stress is a known antecedent to the development of depression in humans and depressive-like states in animals. Whilst there is a clear relationship between stress and motivational drive, the mechanisms underpinning this association remain unclear. One hypothesis is that the endocrine system, via corticotropin-releasing hormone (CRH) in the paraventricular nucleus of the hypothalamus (PVN; PVNCRH), initiates a hormonal cascade resulting in glucocorticoid release, and that excessive glucocorticoids change brain circuit function to produce depression-related symptoms. Another mostly unexplored hypothesis is that the direct activity of PVNCRH neurons and their input to other stress- and reward-related brain regions drives these behaviors. To further understand the direct involvement of PVNCRH neurons in motivation, we used optogenetic stimulation to activate these neurons 1 h/day for 5 consecutive days and showed increased acute stress-related behaviors and long-lasting deficits in the motivational drive for sucrose. This was associated with increased Fos-protein expression in the lateral hypothalamus (LH). Direct stimulation of the PVNCRH inputs in the LH produced a similar pattern of effects on sucrose motivation. Together, these data suggest that PVNCRH neuronal activity may be directly responsible for changes in motivational drive and that these behavioral changes may, in part, be driven by PVNCRH synaptic projections to the LH.
... Potential sources of CRF to the various DA subregions are, therefore, diverse but have not been well studied (reviewed in Kelly & Fudge, 2018). A large known source of CRF to the rodent and primate ventral midbrain DA system in general arises from the central extended amygdala (Dabrowska et al., 2016;Fudge et al., 2017;Rodaros et al., 2007). ...
Dopamine (DA) is involved in stress and stress‐related illnesses, including many psychiatric disorders. Corticotropin‐releasing factor (CRF) plays a role in stress responses and targets the ventral midbrain DA system, which is composed of DA and non‐DA cells, and divided into specific subregions. Although CRF inputs to the midline A10 nuclei (“classic VTA”) are known, in monkeys, CRF‐containing terminals are also highly enriched in the expanded A10 parabrachial pigmented nucleus (PBP) and in the A8 retrorubral field subregions. We characterized CRF‐labeled synaptic terminals on DA (tyrosine hydroxylase, TH+) and non‐DA (TH–) cell types in the PBP and A8 regions using immunoreactive electron microscopy (EM) in male and female macaques. CRF labeling was present mostly in axon terminals, which mainly contacted TH‐negative dendrites in both subregions. Most CRF‐positive terminals had symmetric profiles. In both PBP and A8, CRF symmetric (putative inhibitory) synapses onto TH‐negative dendrites were significantly greater than asymmetric (putative excitatory) profiles. This overall pattern was similar in males and females, despite shifts in the size of these effects between regions depending on sex. Because stress and gonadal hormone shifts can influence CRF expression, we also did hormonal assays over a 6‐month time period and found little variability in basal cortisol across similarly housed animals at the same age. Together our findings suggest that at baseline, CRF‐positive synaptic terminals in the primate PBP and A8 are poised to regulate DA indirectly through synaptic contacts onto non‐DA neurons.
... However, like other veins of research on MS, relatively little is known regarding the role of the BNST in reward-related behaviors following MS. Given that some VTA-projecting BNST neurons have been found to modulate reward behaviors (Rodaros et al., 2007;Vranjkovic et al., 2014), it seems plausible that MS-altered reward may be in part due to mechanisms in the BNST, but future studies need to clarify this. ...
Nearly one percent of children in the US experience childhood neglect or abuse, which can incite lifelong emotional and behavioral disorders. Many studies investigating the neural underpinnings of maleffects inflicted by early life stress have largely focused on dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. Newer veins of evidence suggest that exposure to early life stressors can interrupt neural development in extrahypothalamic areas as well, including the bed nucleus of the stria terminalis (BNST). One widely used approach in this area is rodent maternal separation (MS), which typically consists of separating pups from the dam for extended periods of time, over several days during the first weeks of postnatal life - a time when pups are highly dependent on maternal care for survival. MS has been shown to incite myriad lasting effects not limited to increased anxiety-like behavior, hyper-responsiveness to stressors, and social behavior deficits. The behavioral effects of MS are widespread and thus unlikely to be limited to hypothalamic mechanisms. Recent work has highlighted the BNST as a critical arbiter of some of the consequences of MS, especially socioemotional behavioral deficits. The BNST is a well-documented modulator of anxiety, reward, and social behavior by way of its connections with hypothalamic and extra-hypothalamic systems. Moreover, during the postnatal period when MS is typically administered, the BNST undergoes critical neural developmental events. This review highlights evidence that MS interferes with neural development to permanently alter BNST circuitry, which may account for a variety of behavioral deficits seen following early life stress. This article is part of the Special Issue on 'Fear, Anxiety and PTSD'.
... Together these studies suggest a more nuanced role for PVN CRH neurons in motivated behaviour, potentially via their projections to brain regions critical for motivation such as the LH or ventral tegmental area (VTA) (21). ...
Impaired motivational drive is a key feature of depression. Chronic stress is a known antecedent to the development of depression in humans and depressive-like states in animals. Whilst there is a clear relationship between stress and motivational drive, the mechanisms underpinning this association remain unclear. One hypothesis is that the endocrine system, via corticotropin-releasing hormone (CRH) in the paraventricular nucleus of the hypothalamus (PVN; PVN CRH ), initiates a hormonal cascade resulting in glucocorticoid release, and that excessive glucocorticoids change brain circuit function to produce depression-related symptoms. Another, mostly unexplored hypothesis is that the direct activity of PVN CRH neurons and their input to other stress- and reward-related brain regions drives these behaviours. To further understand the direct involvement of PVN CRH neurons in motivation, we used optogenetic stimulation to activate these neurons one hour/day for 5 consecutive days and showed increased acute stress-related behaviours and long-lasting deficits in the motivational drive for sucrose. This was associated with increased Fos-protein expression in the lateral hypothalamus (LH). Direct stimulation of the PVN CRH inputs in the LH produced a similar pattern of effects on sucrose motivation. Together, these data suggest that PVN CRH neuronal activity may be directly responsible for changes in motivational drive and that these behavioural changes may, in part, be driven by PVN CRH synaptic projections to the LH.
... Potential sources of CRF to the various DA subregions are therefore diverse, but have not been well studied (reviewed in, Kelly and Fudge, 2018). A large known source of CRF to the rodent and primate ventral midbrain DA system in general arises from the central extended amygdala (Rodaros et al., 2007;Dabrowska et al., 2016;Fudge et al., 2017). ...
Dopamine (DA) is involved in stress and stress-related illnesses, including many psychiatric disorders. Corticotropin-releasing factor (CRF) plays a role in stress responses and targets the ventral midbrain DA system. This system is comprised of DA and non-DA cells and is divided into specific subregions. Although CRF inputs to the midline A10 nuclei of the DA system are well studied in rodents, in monkeys, CRF-containing terminals are also highly enriched in the expanded A10 parabrachial pigmented nucleus (PBP) and in the A8 retrorubral field subregion. In primates, the central extended amygdala, a rich source of CRF afferents across species, preferentially targets the PBP and A8 fields. We thus sought to characterize CRF terminals on DA (tyrosine hydroxylase, TH+) and non-DA (TH-) cell types in the PBP and A8 regions at the ultrastructural level using immuno-reactive electron microscopy (EM) for TH and CRF in male and female macaques. CRF labeling was present mostly in axon terminals, which mainly contacted non-DA dendrites in both subregions. Most CRF-positive terminals had inhibitory (symmetric) profiles. In the A8, CRF symmetric (inhibitory) contacts onto non-DA neurons were significantly greater than asymmetric (excitatory) profiles; this pattern was also seen in the PBP, but did not reach statistical significance. No sex differences were found. Hormonal assays suggested that our animals were at similar developmental stages and experienced similar stress levels. Together our findings suggest that at baseline, CRF terminals in the primate PBP and A8 largely regulate DA indirectly through non-DA neurons.
... Mineralocorticoid receptors, by contrast, modulate fear conditioning [23,24] and regulate dopamine release in the nucleus accumbens (NAc) and the basolateral amygdala [25][26][27]. However, most research has focused on the effects of CRF, rather than corticosterone, in the VTA, as CRF-expressing neurons in the bed nucleus of the stria terminalis, central amygdala, and paraventricular nucleus of the hypothalamus have all been shown to project to the VTA [28][29][30], and a subset of VTA DA neurons express CRF [31]. ...
Stress affects many brain regions, including the ventral tegmental area (VTA), which is critically involved in reward processing. Excessive stress can reduce reward-seeking behaviors but also exacerbate substance use disorders, two seemingly contradictory outcomes. Recent research has revealed that the VTA is a heterogenous structure with diverse populations of efferents and afferents serving different functions. Stress has correspondingly diverse effects on VTA neuron activity, tending to decrease lateral VTA dopamine (DA) neuron activity, while increasing medial VTA DA and GABA neuron activity. Here we review the differential effects of stress on the activity of these distinct VTA neuron populations and how they contribute to decreases in reward-seeking behavior or increases in drug self-administration.
... Future research could also identify which CRF-releasing anatomical projections mediate incentive motivation for cocaine. CRF-containing neurons in CeA project to downstream targets in LH, VP, VTA, PBN and BNST [23,30,[36][37][38]. Projections to LH, VP, or VTA may be primary candidates to mediate incentive motivation, as stimulation of CeA-BNST projections are reliably reported to induce negatively-valenced motivation [37,[39][40][41]. ...
Corticotropin releasing factor (CRF) systems in limbic structures are posited to mediate stress-induced relapse in addiction, traditionally by generating distress states that spur drug consumption as attempts at hedonic self-medication. Yet evidence suggests that activating CRF-expressing neurons in the central amygdala (CeA) or nucleus accumbens (NAc) can magnify incentive motivation in absence of distress, at least for sucrose rewards. However, traditional CRF hypotheses in addiction neuroscience are primarily directed toward drug rewards. The question remains open whether CRF systems can similarly act via incentive motivation mechanisms to promote pursuit of drug rewards, such as cocaine. Here we tested whether optogenetic excitation of CRF-containing neurons in either NAc medial shell, lateral CeA, or dorsolateral BNST of transgenic Crh -Cre+ rats would spur preference and pursuit of a particular laser-paired cocaine reward over an alternative cocaine reward, and whether excitation served as a positively-valenced incentive itself, through laser self-stimulation tests. We report that excitation of CRF-containing neurons in either NAc or CeA recruited mesocorticolimbic circuitry to amplify incentive motivation to pursue the laser-paired cocaine: focusing preference on the laser-paired cocaine reward in a two-choice task, and spurred pursuit as doubled breakpoint in a progressive ratio task. Crucially indicating positive-valence, excitation of CRF neurons in NAc and CeA also was actively sought after by most rats in self-stimulation tasks. Conversely, CRF neuronal activation in BNST was never self-stimulated, but failed to enhance cocaine consumption. Collectively, we find that NAc and CeA CRF-containing neurons can amplify pursuit and consumption of cocaine by positively-valenced incentive mechanisms, without any aversive distress.
... Corticotropin-releasing factor (CRF) is a key neuropeptide in the stress response. CRF is produced by the neurons of multiple hypothalamic and limbic regions including PVN, bed nucleus of the stria terminal is (BNST), and the central amygdala and CRF-containing fibers populate the NAcc core, NAcc medial shell, and the VTA [95][96][97]. Additionally, a subset of VTA DA neurons also co-express CRF [98]. Within the VTA, DA neurons receive mostly asymmetric (excitatory) input from CRF+ terminals, whereas non-DA neurons receive both symmetric (inhibitory) and asymmetric inputs [99,100]. ...
The mesolimbic dopamine system is the primary neural circuit mediating motivation, reinforcement, and reward-related behavior. The activity of this system and multiple behaviors controlled by it are affected by changes in feeding and body weight, such as fasting, food restriction, or the development of obesity. Multiple different peptides and hormones that have been implicated in the control of feeding and body weight interact with the mesolimbic dopamine system to regulate many different dopamine-dependent, reward-related behaviors. In this review, we summarize the effects of a selected set of feeding-related peptides and hormones acting within the ventral tegmental area and nucleus accumbens to alter feeding, as well as food, drug, and social reward.
... There are several processes that may underly attenuated CRFr1 expression after acute stress in CUS rats. A major regulator of the CRFr1 receptor expression is CRF itself (Parham et al., 2004) which is found in a range of structures known to regulate behavioural responses to stress, such as the lateral bed nucleus of stria terminalis, the central nucleus of the amygdala and the paraventricular nucleus of the hypothalamus (Rodaros et al., 2007). Attenuation of the CRF input to the VTA from these structures could in turn have led to attenuated CRFr1 expression. ...
Stress reduces cognitive flexibility and dopamine D1 receptor-related activity in the prelimbic cortex (PL), effects hypothesized to depend on reduced corticotropic releasing factor receptor type 1 (CRFr1) regulation of dopamine neurons in the ventral tegmental area (VTA). We assessed this hypothesis in rats by examining the effect of chronic unpredictable restraint stress (CUS), mild acute stress, or their combination on cognitive flexibility, CRFr1 expression in the VTA and D1-related activity in PL. In Experiment 1, rats received either CUS or equivalent handling for 14 days before being trained to press two levers to earn distinct food outcomes. Initial learning was assessed using an outcome devaluation test after which cognitive flexibility was assessed by reversing the outcomes earned by the actions. Prior to each reversal training session, half the CUS and controls receiving acute stress with action-outcome updating assessed using a second devaluation test and CRFr1 expression in the VTA assessed using in-situ hybridisation. Although CUS did not itself affect action-outcome learning, its combination with acute stress blocked reversal learning and decreased VTA CRFr1 expression after acute shock. The relationship between these latter two effects was assessed in Experiment 2 by pharmacologically disconnecting the VTA and PL, unilaterally blocking neurons expressing CRFr1 in the VTA and D1 receptors in the contralateral PL during reversal learning after acute stress. Acute stress again blocked reversal learning but only in the group with VTA-PL disconnection, demonstrating that VTA CRFr1-induced facilitation of dopaminergic activity in the PL is necessary for maintaining cognitive flexibility after acute stress. [250].
... Areas in the brain with the most CRF include the PVN and amygdala, which are important in the HPA axis response to stress and aversive and negative affective states (Boorse & Denver, 2006;Smith & Vale, 2006). These brain subregions project to and influence the VTA and NAc, both of which are involved in reward processing (Rodaros, Caruana, Amir, & Stewart, 2007). Thus, CRF plays a significant role in inhibiting reward neurocircuitry as well as mediating negative affective states (Bruijnzeel et al., 2012;Grieder et al., 2014). ...
Nicotine and alcohol abuse and co-dependence represent major public health crises. Indeed, previous research has shown that the prevalence of alcoholism is higher in smokers than in non-smokers. Adolescence is a susceptible period of life for the initiation of nicotine and alcohol use and the development of nicotine-alcohol codependence. However, there is a limited number of pharmacotherapeutic agents to treat addiction to nicotine or alcohol alone. Notably, there is no effective medication to treat this comorbid disorder. This chapter aims to review the early nicotine use and its impact on subsequent alcohol abuse during adolescence and adulthood as well as the role of neuropeptides in this comorbid disorder. The preclinical and clinical findings discussed in this chapter will advance our understanding of this comorbid disorder's neurobiology and lay a foundation for developing novel pharmacotherapies to treat nicotine and alcohol codependence.
... Chemogenetic activation or inhibition of CeA CRH neurons bidirectionally modulates anxiety-like behavior, and mediates conditioned flight [49,50]. VTA-innervating CRH neurons have been shown to be located in the bed nucleus of the stria terminals (BNST), PVN, and CeA [51][52][53]. In the current study, we found that CRH neurons in the CeA make monosynaptic connections with the VTA Mor-Ens (Fig. 4d-s). ...
Plasticity of neurons in the ventral tegmental area (VTA) is critical for establishment of drug dependence. However, the remodeling of the circuits mediating the transition between positive and negative effect remains unclear. Here, we used neuronal activity-dependent labeling technique to characterize and temporarily control the VTA neuronal ensembles recruited by the initial morphine exposure (morphine-positive ensembles, Mor-Ens). Mor-Ens preferentially projected to NAc, and induced dopamine-dependent positive reinforcement. Electrophysiology and rabies viral tracing revealed the preferential connections between the VTA-projective corticotrophin-releasing hormone (CRH) neurons of central amygdala (CRHCeA→VTA) and Mor-Ens, which was enhanced after escalating morphine exposure and mediated the negative effect during opiate withdrawal. Pharmacologic intervention or CRISPR-mediated repression of CRHR1 in Mor-Ens weakened the inhibitory CRHCeA→VTA inputs, and alleviated the negative effect during opiate withdrawal. These data suggest that neurons encoding opioid reward experience are inhibited by enhanced CRHCeA→VTA inputs induced by chronic morphine exposure, leading to negative effect during opiate withdrawal, and provide new insight into the pathological changes in VTA plasticity after drug abuse and mechanism of opiate dependence.
... studies could identify the specific projections from CeA, NAc and BNST that mediate these effects. For example, CeA CRF-containing neurons project to LH, VP, VTA, and BNST(Asok et al. 2018; Erb et al. 2001a;Pomrenze et al. 2015 Pomrenze et al. , 2019bRodaros et al. 2007;Ventura-Silva et al. 2020). CeA-BNST CRF-containing projections may reliably mediate aversive motivation(Asok et al. 2018;de Guglielmo et al. 2019; Pomrenze et al. 2019b;Ventura-Silva et al. 2020), implying that projections to LH, VP, VTA or elsewhere may mediate incentive motivation effects. ...
Striatal-level structures such as the nucleus accumbens (NAc) and central amygdala (CeA) are capable of generating intense incentive and aversive motivated behaviors (Baumgartner et al. 2020; Warlow et al. 2020). NAc may have two modes for motivation, as inhibition and excitation of NAc can both produce motivated behaviors. For example, NAc medial shell inhibition through AMPA receptor antagonist (DNQX) microinjections can produce both intense eating and defensive behaviors (Baumgartner et al., 2020). Chapter 2 of this dissertation investigates the inhibition hypothesis of accumbens motivation generation by testing whether local pairing of optogenetic excitation can disrupt ‘desire’ and ‘dread’ behaviors generated by DNQX microinjections. Incentive and aversive motivation generated by NAc and other limbic structures are flexible and able to respond to external stressors. Chapter 3 therefore investigates a previously untested neuronal population in NAc that expresses corticotropin-releasing factor (CRF), a stress-related peptide heavily implicated in aversive motivation and distressing drug-withdrawal states in CeA and bed nucleus of stria terminalis (BNST). Like NAc, the CeA is also capable of producing intense positive and negative motivated behaviors and we investigate the flexibility of incentive or aversive motivation in CRF neurons using new Crh-Cre+ rats to optogenetically stimulate NAc, CeA, or BNST CRF-containing neurons. This work finds that excitation of CRF-expressing neurons is capable of biasing and amplifying motivation for sucrose rewards in both NAc shell and lateral CeA (Baumgartner et al. 2021). Conversely, it also demonstrates that optogenetic excitation of pallidal-like bed nucleus of stria terminalis (BNST) CRF-containing neurons produces only negative affect and aversive motivation, filling the traditional role that CRF has been hypothesized to play in aversive withdrawal and affect (Koob 2013). Following the demonstrated positive role of NAc and CeA CRF-containing neurons for sucrose rewards, Chapter 4 of this dissertation examines whether this influence on incentive motivation also applies to drug rewards. CRF in CeA and BNST is posited to underlie aversive withdrawal states, causing negative distress that leads to addictive relapse through attempts at hedonic self-medication to relieve this state (Koob 2013). Chapter 4 therefore tests whether optogenetic excitation of CRF neurons in NAc, CeA, and BNST are capable of biasing and amplifying motivation for self-administered intravenous cocaine infusions. Understanding whether CRF-mediated incentive motivation also can drive drug motivation is therefore integral. We find that NAc and CeA CRF-expressing neurons are indeed capable of biasing motivation for cocaine infusions, while rats given the option between BNST CRF-containing neuron-paired cocaine and cocaine alone show no drug escalation or preferences between cocaine options. Altogether this dissertation demonstrates the limbic generation of intense motivation in structures such as NAc and CeA, and how both incentive and aversive motivation can be modulated by stress and brain CRF systems. The neural mechanisms underlying these different motivational valences provide important insight into cases where motivation can become pathological, such as in addiction, schizophrenia, and other psychological disorders.
... The BNST is identified as a key player in Crh signaling and studies show that Crh signaling within the BNST increases during both stress and substance abuse [63,72,73]. Anatomical tracer studies show that Crh BNST neurons project to several brain regions including the VTA, LH, dorsal raphe nucleus (DRN), and paraventricular nucleus of the hypothalamus (PVN) [74][75][76][77][78]. Additionally, whole-cell patch recordings identified different electrophysiological patterns in subsets of Crh BNST neurons that can be separated into three groups based on basal resting membrane potentials and firing patterns [77,79]. ...
Over the past few decades, the bed nucleus of the stria terminalis (BNST) gained popularity as a unique brain region involved in regulating motivated behaviors related to neuropsychiatric disorders. The BNST, a component of the extended amygdala, consists of a variety of subnuclei and neuronal ensembles. Multiple studies have highlighted the BNST as playing a fundamental role in integrating information by interfacing with other brain regions to regulate distinct aspects of motivated behaviors associated with stress, anxiety, depression, and decision-making. However, due to the high molecular heterogeneity found within BNST neurons, the precise mechanisms by which this region regulates distinct motivational states remains largely unclear. Single-cell RNA sequencing data have revealed that the BNST consists of multiple genetically identifiable cell-type clusters. Contemporary tools can therefore be leveraged to target and study such cell-types and elucidate their precise functional role. In this review, we discuss the different subsets of neurons found in the BNST, their anatomical distribution, and what is currently known about BNST cell-types in regulating motivated behaviors.
... The activity of CRF in extrahypothalamic regions contributes to depression, anxiety, and fear-related behaviors (Binder and Nemeroff, 2009;Sanford et al., 2017;Paretkar and Dimitrov, 2018). The CeA contains CRF-positive neurons (Rodaros et al., 2007), whereas the BLA contains numerous CRF receptor-positive projection neurons (Roozendaal et al., 2002). Increased CRF in the BLA can impair memory consolidation (Narla et al., 2019), whereas increased CRF in the nucleus accumbens leads to depressive behaviors likely by modulating extracellular acetylcholine (Chen et al., 2012); CRF receptor 1 antagonists exhibit antidepressant activity (Overstreet and Griebel, 2004). ...
Mild traumatic brain injury (TBI) results in chronic affective disorders such as depression, anxiety, and fear that persist up to years following injury and significantly impair the quality of life for patients. Although a great deal of research has contributed to defining symptoms of mild TBI, there are no adequate drug therapies for brain-injured individuals. Preclinical studies have modeled these deficits in affective behaviors post-injury to understand the underlying mechanisms with a view to developing appropriate treatment strategies. These studies have also unveiled sex differences that contribute to the varying phenotypes associated with each behavior. Although clinical and preclinical studies have viewed these behavioral deficits as separate entities with unique neurobiological mechanisms, mechanistic similarities suggest that a novel approach is needed to advance research on drug therapy. This review will discuss the circuitry involved in the expression of deficits in affective behaviors following mild TBI in humans and animals and provide evidence that the manifestation of impairment in these behaviors stems from an amygdala-dependent emotional processing deficit. It will highlight mechanistic similarities between these different types of affective behaviors that can potentially advance mild TBI drug therapy by investigating treatments for the deficits in affective behaviors as one entity, requiring the same treatment.
... Additionally, there are neuronal networks that extend between hypothalamic and mesocorticolimbic regions that may regulate the consumption of palatable food and drugs of abuse. Hypothalamic neurons can project to other hypothalamic subregions as well as to extra-hypothalamic regions, such as from the PVN to the VTA (Rodaros et al., 2007). Projections from the lateral hypothalamus extend to amygdala, NAc, VTA, and prefrontal cortex, and these regions also project back to the hypothalamus (Beckstead et al., 1979;Kita and Oomura, 1981;Fadel and Deutch, 2002;Kampe et al., 2009). ...
The prevalence of psychiatry disorders such as anxiety and depression has steadily increased in recent years in the United States. This increased risk for anxiety and depression is associated with excess weight gain, which is often due to over-consumption of western diets that are typically high in fat, as well as with binge eating disorders, which often overlap with overweight and obesity outcomes. This finding suggests that diet, particularly diets high in fat, may have important consequences on the neurocircuitry regulating emotional processing as well as metabolic functions. Depression and anxiety disorders are also often comorbid with alcohol and substance use disorders. It is well-characterized that many of the neurocircuits that become dysregulated by overconsumption of high fat foods are also involved in drug and alcohol use disorders, suggesting overlapping central dysfunction may be involved. Emerging preclinical data suggest that high fat diets may be an important contributor to increased susceptibility of binge drug and ethanol intake in animal models, suggesting diet could be an important aspect in the etiology of substance use disorders. Neuroinflammation in pivotal brain regions modulating metabolic function, food intake, and binge-like behaviors, such as the hypothalamus, mesolimbic dopamine circuits, and amygdala, may be a critical link between diet, ethanol, metabolic dysfunction, and neuropsychiatric conditions. This brief review will provide an overview of behavioral and physiological changes elicited by both diets high in fat and ethanol consumption, as well as some of their potential effects on neurocircuitry regulating emotional processing and metabolic function.
... Future studies could identify the specific projections from the CeA, NAc, and BNST that mediate these effects. For example, CeA CRF-containing neurons project to the LH, VP, VTA, and BNST (21,(52)(53)(54)(55)(56). CeA-BNST CRF-containing projections may reliably mediate aversive motivation (35,(53)(54)(55), implying that projections to the LH, VP, VTA, or elsewhere may mediate incentive motivation effects. ...
Background
Corticotropin releasing factor (CRF) neural systems are important stress mechanisms in central amygdala (CeA), bed nucleus of stria terminalis (BNST), nucleus accumbens (NAc) and related structures. CRF-containing neural systems are traditionally posited to generate aversive distress states that motivate over-consumption of rewards and relapse in addiction. However, CRF-containing systems may alternatively promote incentive motivation to increase reward pursuit and consumption, without requiring aversive states.
Methods
We optogenetically stimulated CRF-expressing neurons in CeA, BNST or NAc, using Crh-Cre+ rats (n=37 female, n=34 male) to investigate roles in incentive motivation versus aversive motivation. We paired CRF-expressing neuronal stimulations with earning sucrose rewards in two-choice and progressive ratio tasks and investigated recruitment of distributed limbic circuitry. We further assessed valence with CRF-containing neuron laser self-stimulation tasks.
Results
Channelrhodopsin excitation of CRF-containing neurons in CeA and NAc amplified and focused incentive motivation and recruited activation of mesocorticolimbic reward circuitry. CRF systems in both CeA and NAc supported laser self-stimulation, amplified incentive motivation for sucrose in a breakpoint test, and focused ‘wanting’ on laser-paired sucrose over a sucrose alternative in a two-choice test. Conversely, stimulation of CRF-containing neurons in BNST produced negative-valence or aversive effects and recruited distress-related circuitry, as stimulation was avoided and suppressed motivation for sucrose.
Conclusions
CRF-containing systems in NAc and CeA can promote reward consumption by increasing incentive motivation, without involving aversion. By contrast, stimulation of CRF-containing systems in BNST is aversive but suppresses sucrose reward pursuit and consumption, rather than increase as predicted by traditional hedonic self-medication hypotheses.
... Likewise, in rats raised in social isolation, increased levels of dopamine were released into the nucleus accumbens and dorsomedial striatum, as detected by voltammetry in brain slices (Yorgason et al., 2016). By this mechanism, social stress enhanced conditioning to reward-related sensory inputs (Polter & Kauer, 2014;Tovar-Diaz, Pomrenze, Kan, Pahlavan, & Morikawa, 2018;Rodaros, Caruana, Amir, & Stewart, 2007). ...
We review the role of childhood abuse (CA) in the practice of impulsive, risk-taking behaviors during adulthood. CA deregulates the adult response to stress, which in turn disrupts the prefrontal-striatal systems that provide executive control over reward-related behavior. The result is impulsivity and risk-taking, including self-medication with drugs and alcohol and the practice of unsafe sex. These behaviors decrease quality of life and impair the attainment of long-term goals. Risky sexual behavior, in particular, increases the chance of HIV infection and perpetuates the epidemic.
... [11][12][13] This peptide and its receptors CRF1R and CRF2R are expressed in the hypothalamus, as well as in limbic brain areas including amygdala and bed nucleus of stria terminalis (BNST). 14,15 Several studies also showed that p38 MAPK (MAPK14) is involved in stress and anxiety. Indeed, p38 MAPK was reported to be activated after stress [16][17][18] in many different regions of the brain including the prefrontal cortex, nucleus accumbens, and the hippocampus. ...
Social interaction in an alternative context can be beneficial against drugs of abuse. Stress is known to be a risk factor that can exacerbate the effects of addictive drugs. In this study, we investigated whether the positive effects of social interaction are mediated through a decrease in stress levels. For that purpose, rats were trained to express cocaine or social interaction conditioned place preference (CPP). Behavioural, hormonal, and molecular stress markers were evaluated. We found that social CPP decreased the percentage of incorrect transitions of grooming and corticosterone to the level of naïve untreated rats. In addition, corticotropin-releasing factor (CRF) was increased in the bed nucleus of stria terminalis after cocaine CPP. In order to study the modulation of social CPP by the CRF system, rats received intracerebroventricular CRF or alpha-helical CRF, a nonselective antagonist of CRF receptors. The subsequent effects on CPP to cocaine or social interaction were observed. CRF injections increased cocaine CPP, whereas alpha-helical CRF injections decreased cocaine CPP. However, alpha-helical CRF injections potentiated social CPP. When social interaction was made available in an alternative context, CRF-induced increase of cocaine preference was reversed completely to the level of rats receiving cocaine paired with alpha-helical CRF. This reversal of cocaine preference was also paralleled by a reversal in CRF-induced increase of p38 MAPK expression in the nucleus accumbens shell. These findings suggest that social interaction could contribute as a valuable component in treatment of substance use disorders by reducing stress levels.
... In the brain, the areas with the highest expression of CRF include the paraventricular nucleus of the hypothalamus (PVN), which secretes CRF during the activation of the HPA axis stress response and the extended amygdala that is implicated in negative affect and fear response (Boorse andDenver, 2006, Smith and. Those CRF projections to extrahypothalamic structures eventually reach and influence the activity of the VTA and NAc in the mesolimbic reward pathway (Rodaros et al., 2007). Thus, it is well established by research that the CRF system plays an important role in anxiety and negative affect as well as in inhibiting the brain reward system Grieder et al., 2014). ...
Smoking represents one of the greatest preventable causes of death globally, and pharmacological treatments of higher efficacy targeting smoking cessation are necessary. Current drug interventions show only modest success rates and do not adequately address nicotine withdrawal-induced anxiety that is heavily implicated in relapse and failed quit attempts. The purpose of this paper is to highlight that nicotine dependence is at least partially maintained through the negative reinforcing effect of avoiding abstinence-induced anxiety. This paper presents findings which suggest that this effect is mediated by the activation of the Corticotropin-Releasing Factor (CRF) system are presented and the implications of a therapeutic agent containing a CRF_1 antagonistare discussed. Specifically, CRF_1 blockers are highlighted as alternatives for individuals with multiple failed quit attempts because they target the abstinence-induced increased anxiety that seems to lie at the core of failed cessation attempts.
... CRH is densely expressed in the paraventricular nucleus of the hypothalamus (PVN) from where it regulates hypothalamic-pituitary-adrenal (HPA) axis activity and consequently the circadian and stress-mediated release of glucocorticoids. Together with its high affinity type 1 receptor (CRHR1), CRH is also involved in modulating behavioral adaptations to stress, which can be attributed to their wide distribution within the mammalian brain including the cortex, key limbic structures and midbrain monoaminergic nuclei (Swanson et al., 1983;Van Pett et al., 2000;Rodaros et al., 2007;Refojo et al., 2011;Dedic et al., 2018a). ...
Dysregulation of the corticotropin-releasing hormone (CRH) system has been implicated in stress-related psychopathologies such as depression and anxiety. Although most studies have linked CRH/CRH receptor 1 signaling to aversive, stress-like behavior, recent work has revealed a crucial role for distinct CRH circuits in maintaining positive emotional valence and appetitive responses under baseline conditions. Here we addressed whether deletion of CRH, specifically from GABAergic forebrain neurons (CrhCKO–GABA mice) differentially affects general behavior under baseline and chronic stress conditions. Expression mapping in CrhCKO–GABA mice revealed absence of Crh in GABAergic neurons of the cortex and limbic regions including the hippocampus, central nucleus of the amygdala and the bed nucleus of the stria terminals, but not in the paraventricular nucleus of hypothalamus. Consequently, conditional CRH knockout animals exhibited no alterations in circadian and stress-induced corticosterone release compared to controls. Under baseline conditions, absence of Crh from forebrain GABAergic neurons resulted in social interaction deficits but had no effect on other behavioral measures including locomotion, anxiety, immobility in the forced swim test, acoustic startle response and fear conditioning. Interestingly, following exposure to chronic social defeat stress, CrhCKO–GABA mice displayed a resilient phenotype, which was accompanied by a dampened, stress-induced expression of immediate early genes c-fos and zif268 in several brain regions. Collectively our data reveals the requirement of GABAergic CRH circuits in maintaining appropriate social behavior in naïve animals and further supports the ability of CRH to promote divergent behavioral states under baseline and severe stress conditions.
... Studies conducted in rats suggest heightened CRF sensitivity in females as compared to males (Bangasser et al., 2010(Bangasser et al., , 2013. Release of limbic CRF can modulate HPA axis activity and monoamine systems implicated in mood and cognition (Rodaros et al., 2007;Valentino & Van Bockstaele, 2008;Wanat et al., 2008). Increased CRF sensitivity in female rats was associated with sex differences in CRF1 receptor signalling and trafficking in the LC-NE system, decreasing their ability to adapt to chronic stressors ( Curtis et al., 2006;Bangasser et al., 2010;Bangasser & Valentino, 2012) (see Table 2). ...
Major depressive disorder (MDD) is a chronic and recurrent psychiatric condition characterized by depressed mood, social isolation and anhedonia. It will affect 20% of individuals with considerable economic impacts. Unfortunately, 30-50% of depressed individuals are resistant to current antidepressant treatments. MDD is twice as prevalent in women and associated symptoms are different. Depression's main environmental risk factor is chronic stress and women report higher levels of stress in daily life. However, not every stressed individual becomes depressed, highlighting the need to identify biological determinants of stress vulnerability but also resilience. Based on a reverse translational approach, rodent models of depression were developed to study the mechanisms underlying susceptibility vs resilience. Indeed, a subpopulation of animals can display coping mechanisms and a set of biological alterations leading to stress resilience. The aetiology of MDD is multifactorial and involves several physiological systems. Exacerbation of endocrine and immune responses from both innate and adaptive systems are observed in depressed individuals and mice exhibiting depression-like behaviours. Increasing attention has been given to neurovascular health since higher prevalence of cardiovascular diseases is found in MDD patients and inflammatory conditions are associated with depression, treatment resistance and relapse. Here we provide an overview of endocrine, immune and vascular changes associated with stress vulnerability vs resilience in rodents and when available, in humans. Lack of treatment efficacy suggest that neuron-centric treatments do not address important causal biological factors and better understanding of stress-induced adaptations, including sex differences, could contribute to develop novel therapeutic strategies including personalized medicine approaches.
... Deep brain stimulation of the BNST has yielded sustained symptom relief in obsessions and compulsions in otherwise refractory OCD (Nuttin et al., 1999(Nuttin et al., , 2013Raymaekers et al., 2017;Winter et al., 2018). A collection of several sexually dimorphic interconnected nuclei, the BNST is part of the extended amygdala with extensive bi-directional connectivity with the CLSTC-loop and beyond (Prewitt and Herman, 1998;McDonald et al., 1999;Dong et al., 2001;Hasue and Shammah-Lagnado, 2002;Dong and Swanson, 2003, 2004b, 2006aRodaros et al., 2007;Li and Kirouac, 2008;Avery et al., 2014;Gregory et al., 2019). Functionally, the BNST filters and/or integrates multiple ascending modalities, mapping with adequate resolution, interoceptive information onto motivational systems for adaptive physiological and behavioral outcomes (Jennings et al., 2013;Kim et al., 2013;Lebow and Chen, 2016). ...
A compulsive phenotype characterizes several neuropsychiatric illnesses – including but not limited to – schizophrenia and obsessive compulsive disorder. Because of its perceived etiological heterogeneity, it is challenging to disentangle the specific neurophysiology that precipitates compulsive behaving. Using polydipsia (or non-regulatory water drinking), we describe candidate neural substrates of compulsivity. We further postulate that aberrant neuroplasticity within cortically projecting structures [i.e., the bed nucleus of the stria terminalis (BNST)] and circuits that encode homeostatic emotions (thirst, hunger, satiety, etc.) underlie compulsive drinking. By transducing an inaccurate signal that fails to represent true homeostatic state, cortical structures cannot select appropriate and adaptive actions. Additionally, augmented dopamine (DA) reactivity in striatal projections to and from the frontal cortex contribute to aberrant homeostatic signal propagation that ultimately biases cortex-dependent behavioral selection. Responding becomes rigid and corresponds with both erroneous, inflexible encoding in both bottom-up structures and in top-down pathways. How aberrant neuroplasticity in circuits that encode homeostatic emotion result in the genesis and maintenance of compulsive behaviors needs further investigation.
... This idea is supported by anatomical observations demonstrating strong interactions between the DA and CRF systems (Kelly and Fudge, 2018). In rodents, the ventral tegmental area (VTA) receives CRF innervation from the lateral BNST, CeA, and the PVN (Rodaros et al., 2007;Dabrowska et al., 2016), and both CRF1 and CRF2 receptors are localized within the DA cell body region of this structure (Van Pett et al., 2000;Tan et al., 2017). Moreover, the NAc contains local CRF cell bodies (Swanson et al., 1983;Merchenthaler et al., 1984) and fibers that may originate from the thalamic paraventricular nucleus, BNST, basolateral amygdala, and mPFC (Itoga et al., 2019). ...
The neuropeptide, corticotropin-releasing factor (CRF), is a key modulator of physiological, endocrine, and behavioral responses during stress. Dysfunction of the CRF system has been observed in stress-related affective disorders including post-traumatic stress disorder, depression, and anxiety. Beyond affective symptoms, these disorders are also characterized by impaired cognition, for which current pharmacological treatments are lacking. Thus, there is a need for pro-cognitive treatments to improve quality of life for individuals suffering from mental illness. In this review, we highlight research demonstrating that CRF elicits potent modulatory effects on higher-order cognition via actions within the prefrontal cortex and subcortical monoaminergic and cholinergic systems. Additionally, we identify questions for future preclinical research on this topic, such as the need to investigate sex differences in the cognitive and microcircuit actions of CRF, and whether CRF may represent a pharmacological target to treat cognitive dysfunction. Addressing these questions will provide new insight into pathophysiology underlying cognitive dysfunction and may lead to improved treatments for neuropsychiatric disorders.
... Anatomical and functional studies reveal connections between CRF and the mesolimbic dopaminergic system. Thus, VTA and NAc receive CRF-positive projections from the PVN and stress extrahypothalamic areas [36,37], which have been proposed to regulate dopamine release. The rewarding effect of morphine (CPP expression) is decreased by pretreatment with CP-154,526, a selective CRF1 antagonist, suggesting an important role of CRF/CRF1 receptor in memory formation and consolidation [30]. ...
The midbrain dopamine system is a sophisticated hub that integrates diverse inputs to control multiple physiological functions, including locomotion, motivation, cognition, reward, as well as maternal and reproductive behaviors. Dopamine is a neurotransmitter that binds to G-protein-coupled receptors. Dopamine also works together with other neurotransmitters and various neuropeptides to maintain the balance of synaptic functions. The dysfunction of the dopamine system leads to several conditions, including Parkinson’s disease, Huntington’s disease, major depression, schizophrenia, and drug addiction. The ventral tegmental area (VTA) has been identified as an important relay nucleus that modulates homeostatic plasticity in the midbrain dopamine system. Due to the complexity of synaptic transmissions and input–output connections in the VTA, the structure and function of this crucial brain region are still not fully understood. In this review article, we mainly focus on the cell types, neurotransmitters, neuropeptides, ion channels, receptors, and neural circuits of the VTA dopamine system, with the hope of obtaining new insight into the formation and function of this vital brain region.
Stress has a strong influence on mental health around the world. Decades of research has sought to identify mechanisms through which stress contributes to psychiatric disorders such as depression, to potentially guide the development of therapeutics targeting stress systems. The hypothalamic pituitary adrenal (HPA) axis is the key endocrine system that is responsible for coordinating body-wide changes that are necessary for survival under stress, and much of the research aimed at understanding the mechanisms by which stress contributes to depression has focussed on HPA axis dysfunction. Corticotrophin releasing hormone (CRH) neurons in the paraventricular nucleus of the hypothalamus (PVN) sit at the apex of the HPA axis, integrating signals relevant to stress and external threats, to ensure HPA axis activity is appropriate for the given context. In addition to this, emerging research has demonstrated that neural activity in PVNCRH neurons regulates stress related behaviours via modulation of downstream synaptic targets. This review will summarize convergent evidence from preclinical studies on chronic stress and clinical research in mood disorders demonstrating changes in PVNCRH neural function, consider how this may influence synaptic targets of PVNCRH neurons, and discuss the potential role of these PVNCRH synaptic pathways in the development of maladaptive behaviours following chronic stress that are relevant to depression. We will also highlight important questions for future research aimed at precisely dissecting endocrine and synaptic roles of PVNCRH neurons in chronic stress, their potential interactions, and therapeutic opportunities for the treatment of stress related disorders.
Ethanol (EtOH) has effects on numerous cellular molecular targets, and alterations in synaptic function are prominent among these effects. Acute exposure to EtOH activates or inhibits the function of proteins involved in synaptic transmission, while chronic exposure often produces opposing and/or compensatory/homeostatic effects on the expression, localization, and function of these proteins. Interactions between different neurotransmitters (e.g., neuropeptide effects on release of small molecule transmitters) can also influence both acute and chronic EtOH actions. Studies in intact animals indicate that the proteins affected by EtOH also play roles in the neural actions of the drug, including acute intoxication, tolerance, dependence, and the seeking and drinking of EtOH. The present chapter is an update of our previous Lovinger and Roberto (Curr Top Behav Neurosci 13:31-86, 2013) chapter and reviews the literature describing these acute and chronic synaptic effects of EtOH with a focus on adult animals and their relevance for synaptic transmission, plasticity, and behavior.
Nearly one percent of children in the US experience childhood neglect or abuse, which can incite lifelong emotional and behavioral disorders. Many studies investigating the neural underpinnings of maleffects inflicted by early life stress have largely focused on dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. Newer veins of evidence suggest that exposure to early life stressors can interrupt neural development in extrahypothalamic areas as well, including the bed nucleus of the stria terminalis (BNST). One widely used approach in this area is rodent maternal separation (MS), which typically consists of separating pups from the dam for extended periods of time, over several days during the first weeks of postnatal life - a time when pups are highly dependent on maternal care for survival. MS has been shown to incite myriad lasting effects not limited to increased anxiety-like behavior, hyper-responsiveness to stressors, and social behavior deficits. The behavioral effects of MS are widespread and thus unlikely to be limited to hypothalamic mechanisms. Recent work has highlighted the BNST as a critical arbiter of some of the consequences of MS, especially socioemotional behavioral deficits. The BNST is a well-documented modulator of anxiety, reward, and social behavior by way of its connections with hypothalamic and extra-hypothalamic systems. Moreover, during the postnatal period when MS is typically administered, the BNST undergoes critical neural developmental events. This review highlights evidence that MS interferes with neural development to permanently alter BNST circuitry, which may account for a variety of behavioral deficits seen following early life stress.
The corticotropin releasing hormone cells in the paraventricular nucleus of the hypothalamus (CRH PVN ) control the slow endocrine response to stress. The synapses on these cells are exquisitely sensitive to acute stress, leveraging local signals to leave a lasting imprint on this system. Additionally, recent work indicates these cells also play key roles in the control of distinct stress and survival behaviors. Here we review these observations and provide a perspective on the role of CRH PVN neurons as integrative and malleable hubs for behavioral, physiological and endocrine responses to stress.
The evoked release of corticotropin-releasing hormone (CRH) from nerve endings at the median eminence is the single-most powerful endocrine trigger for the hormonal cascade known as the hypothalamo-pituitary-adrenal (HPA) axis. CRH-containing neurons cluster in the paraventricular nucleus of the hypothalamus (PVN). Even though the functional heterogeneity and likely subclasses of CRH neurons beyond regulating the stress response were proposed, their molecular identity remained unresolved until the introduction of single-cell RNA-seq. Here, we review recent advances in single-cell RNA-seq to identify molecularly distinct subclasses of Crh-expressing neurons in the PVN, their developmental trajectories, neurotransmitter phenotypes and neuropeptide contents. We take advantage of the repertoire of receptor-coding mRNAs in Crh-expressing neurons of the PVN to predict their circuit motifs, whose wiring and outputs are distinct from other Crh-expressing neurons in the nervous system.
Increased glucocorticoids characterise acute pain responses, but not the chronic pain state, suggesting specific modifications to the HPA‐axis preventing the persistent nature of chronic pain from elevating basal glucocorticoid levels. Individuals with chronic pain mount normal HPA‐axis responses to acute stressors, indicating a rebalancing of the circuits underpinning these responses. Preclinical models of chronic neuropathic pain generally recapitulate these clinical observations, but few studies have considered that the underlying neuroendocrine circuitry may be altered. Additionally, individual differences in the behavioural outcomes of these pain models, which are strikingly similar to the range of behavioural subpopulations that manifest in response to stress, threat and motivational cues, may also be reflected in divergent patterns of HPA‐axis activity, which characterises these other behavioural subpopulations. We investigated the effects of sciatic nerve chronic construction injury (CCI) on adrenocortical and hypothalamic markers of HPA‐axis activity in the subpopulation of rats showing persistent changes in social interactions after CCI (Persistent Effect) and compared them with rats that do not show these changes (No Effect). Basal plasma corticosterone did not change after CCI and did not differ between groups. However, adrenocortical sensitivity to ACTH diverged between these groups. No Effect rats showed large increases in basal plasma ACTH with no change in adrenocortical MC2R expression, whereas Persistent Effect rats showed modest decreases in plasma ACTH and large increases in MC2R expression. In the paraventricular nucleus of the hypothalamus of Persistent Effect rats, single labelling revealed significantly increased numbers of CRF+ve and GR+ve neurons. Double‐labelling revealed fewer GR+ve CRF+vs neurons, suggesting a decreased hypothalamic sensitivity of CRF neurons to circulating corticosterone in Persistent Effect rats. We suggest that in addition to rebalancing the HPA‐axis, the increased CRF expression in Persistent Effect rats contributes to changes in complex behaviours, and in particular social interactions.
Alcohol dependence is characterized by a shift in motivation to consume alcohol from positive reinforcement (i.e., increased likelihood of future alcohol drinking based on its rewarding effects) to negative reinforcement (i.e., increased likelihood of future alcohol drinking based on alcohol-induced reductions in negative affective symptoms, including but not limited to those experienced during alcohol withdrawal). The neural adaptations that occur during this transition are not entirely understood. Mesolimbic reinforcement circuitry (i.e., ventral tegmental area [VTA] neurons) is activated during early stages of alcohol use, and may be involved in the recruitment of brain stress circuitry (i.e., extended amygdala) during the transition to alcohol dependence, after chronic periods of high-dose alcohol exposure. Here, we review the literature regarding the role of canonical brain reinforcement (VTA) and brain stress (extended amygdala) systems, and the connections between them, in acute, sub-chronic, and chronic alcohol response. Particular emphasis is placed on preclinical models of alcohol use.
This article is part of the special Issue on ‘Neurocircuitry Modulating Drug and Alcohol Abuse'.
This review updates three key concepts of autonomic neuroscience—stress, the autonomic nervous system (ANS), and homeostasis. Hans Selye popularized stress as a scientific idea. He defined stress variously as a stereotyped response pattern, a state that evokes this pattern, or a stimulus that evokes the state. According to the “homeostat” theory stress is a condition where a comparator senses a discrepancy between sensed afferent input and a response algorithm, the integrated error signal eliciting specific patterns of altered effector outflows. Scientific advances since Langley's definition of the ANS have incited the proposal here of an “extended autonomic system,” or EAS, for three reasons. (1) Several neuroendocrine systems are bound inextricably to Langley's ANS. The first to be described, by Cannon in the early 1900s, involves the hormone adrenaline, the main effector chemical of the sympathetic adrenergic system. Other neuroendocrine systems are the hypothalamic-pituitary-adrenocortical system, the arginine vasopressin system, and the renin-angiotensin-aldosterone system. (2) An evolving body of research links the ANS complexly with inflammatory/immune systems, including vagal anti-inflammatory and catecholamine-related inflammasomal components. (3) A hierarchical network of brain centers (the central autonomic network, CAN) regulates ANS outflows. Embedded within the CAN is the central stress system conceptualized by Chrousos and Gold. According to the allostasis concept, homeostatic input-output curves can be altered in an anticipatory, feed-forward manner; and prolonged or inappropriate allostatic adjustments increase wear-and-tear (allostatic load), resulting in chronic, stress-related, multi-system disorders. This review concludes with sections on clinical and therapeutic implications of the updated concepts offered here.
During the past 30 years, investigating the physiology of eating behaviors has generated a truly vast literature. This is fueled in part by a dramatic increase in obesity and its comorbidities that has coincided with an ever increasing sophistication of genetically based manipulations. These techniques have produced results with a remarkable level of cell-specificity-particularly at the cell signaling level-and have played a lead role in advancing the field. However, putting these findings into a brain-wide context that connects physiological signals and neurons to behavior and somatic physiology requires a thorough consideration of neuronal connections; a field that has also seen an extraordinary technological revolution. Our goal is to present a comprehensive and balanced assessment of how physiological signals associated with energy homeostasis interact at many brain levels to control eating behaviors. A major theme is that these signals engage sets of interacting neural networks throughout the brain, that are defined by specific neural connections. We begin by discussing some fundamental concepts-including ones that still engender vigorous debate-that provide the necessary frameworks for understanding how the brain controls meal initiation and termination. These include: key word definitions, ATP availability as the pivotal regulated variable in energy homeostasis, neuropeptide signaling, homeostatic and hedonic eating, and meal structure. Within this context, we discuss network models of how key regions in the endbrain (or telencephalon), hypothalamus, hindbrain, medulla, vagus nerve, and spinal cord work together with the gastrointestinal tract to enable the complex motor events that permit animals to eat in diverse situations.
Drugs of abuse leads to adaptive changes in the brain stress system, and produces negative affective states including aversion and anxiety after drug use is terminated. Corticotrophin-releasing hormone (CRH) is the main transmitter in control of response to stressors and is neuronal enriched in the central amygdala (CeA), a sub-region of the extended amygdala playing an important role in integrating emotional information and modulating stress response. The effect of CRH neurons in CeA on the negative emotions on morphine naïve and withdrawal mice is unclear. Thus, we utilized CRH-Cre transgenic mice injected with AAV-mediated Designer Receptors Exclusively Activated By Designer Drugs (DREADDs) to chemogenetically manipulate CRH neurons in CeA. And methods of behavior analysis, including conditioned place aversion (CPA), elevated plus maze and locomotor activity tests, were used to investigate morphine withdrawal-induced negative emotions in mice. The results showed that, inhibiting CRH neurons of CeA decreased the formation of morphine withdrawal-induced CPA, as well as the anxiety level of CRH-Cre mice. Furthermore, specifically activating CRH neurons in CeA evoked CPA and anxiety of morphine naïve mice. Neither inhibiting nor activating CRH neurons had effects on their locomotor activity. These results suggest that CRH neurons in CeA are involved in the mediation of morphine withdrawal-induced negative emotion in mice, providing a theoretical basis for drug addiction and relapse mechanism.
Disrupted operation of the reward circuitry underlies many aspects of affective disorders. Such disruption may manifest as aberrant behavior including risk taking, depression, anhedonia, and addiction. Early-life adversity is a common antecedent of adolescent and adult affective disorders involving the reward circuitry. However, whether early-life adversity influences the maturation and operations of the reward circuitry, and the potential underlying mechanisms, remain unclear. Here, we present novel information using cutting-edge technologies in animal models to dissect out the mechanisms by which early-life adversity provokes dysregulation of the complex interactions of stress and reward circuitries. We propose that certain molecularly defined pathways within the reward circuitry are particularly susceptible to early-life adversity. We examine regions and pathways expressing the stress-sensitive peptide corticotropin-releasing factor (CRF), which has been identified in critical components of the reward circuitry and interacting stress circuits. Notably, CRF is strongly modulated by early-life adversity in several of these brain regions. Focusing on amygdala nuclei and their projections, we provide evidence suggesting that aberrant CRF expression and function may underlie augmented connectivity of the nucleus accumbens with fear/anxiety regions, disrupting the function of this critical locus of pleasure and reward.
Neuroadaptations in brain regions that regulate emotional and reward-seeking behaviors have been suggested to contribute to pathological behaviors associated with alcohol-use disorder. One such region is the bed nucleus of the stria terminalis (BNST), which has been linked to both alcohol consumption and alcohol withdrawal-induced anxiety and depression. Recently, we identified a GABAergic microcircuit in the BNST that regulates anxiety-like behavior. In the present study, we examined how chronic alcohol exposure alters this BNST GABAergic microcircuit in mice. We selectively targeted neurons expressing corticotropin releasing factor (CRF) using a CRF-reporter mouse line and combined retrograde labeling to identify BNST projections to the ventral tegmental area (VTA) and lateral hypothalamus (LH). Following 72 h of withdrawal from four weekly cycles of chronic intermittent ethanol (CIE) vapor exposure, the excitability of a sub-population of putative local CRF neurons that did not project to either VTA or LH (CRFnon−VTA/LH neurons) was increased. Withdrawal from CIE also increased excitability of non-CRF BNST neurons that project to both LH and VTA (BNSTnon−CRF-proj neurons). Furthermore, both populations of neurons had a reduction in spontaneous EPSC amplitude while frequency was unaltered. Withdrawal from chronic alcohol was accompanied by a significant increase in spontaneous IPSC frequency selectively in the BNSTnon−CRF-proj neurons. Together, these data suggest that withdrawal from chronic ethanol dysregulates local CRF-GABAergic microcircuit to inhibit anxiolytic outputs of the BNST which may contribute to enhanced anxiety during alcohol withdrawal and drive alcohol-seeking behavior.
This article is part of the special issue on ‘Neuropeptides’.
Exposure to acute intermittent hypoxia (AIH) induces a progressive increase of sympathetic nerve activity (SNA) that reflects a form of neuroplasticity known as sympathetic long-term facilitation (sLTF). Our recent findings indicate that activity of neurons in the hypothalamic paraventricular nucleus (PVN) contributes to AIH-induced sLTF, but neither the intra-PVN distribution nor the neurochemical identity of AIH responsive neurons has been determined. Here, awake rats were exposed to 10 cycles of AIH and c-Fos immunohistochemistry was performed to identify transcriptionally activated neurons in rostral, middle and caudal planes of the PVN. Effects of graded intensities of AIH were investigated in separate groups of rats (n = 6/group) in which inspired oxygen (O2) was reduced every 6 min from 21% to nadirs of 10%, 8% or 6%. All intensities of AIH failed to increase c-Fos counts in the caudally located lateral parvocellular region of the PVN. c-Fos counts increased in the dorsal parvocellular and central magnocellular regions, but significance was achieved only with AIH to 6% O2 (P < 0.002). By contrast, graded intensities of AIH induced graded c-Fos activation in the stress-related medial parvocellular (MP) region. Focusing on AIH exposure to 8% O2, experiments next investigated the stress-regulatory neuropeptide content of AIH-activated MP neurons. Tissue sections immunostained for corticotropin-releasing hormone (CRH) or arginine vasopressin (AVP) revealed a significantly greater number of neurons stained for CRH than AVP (P < 0.0001), though AIH induced expression of c-Fos in a similar fraction (~14%) of each neurochemical class. Amongst AIH-activated MP neurons, ~30% stained for CRH while only ~2% stained for AVP. Most AIH-activated CRH neurons (~82%) were distributed in the rostral one-half of the PVN. Results indicate that AIH recruits CRH, but not AVP, neurons in rostral to middle levels of the MP region of PVN, and raise the possibility that these CRH neurons may be a substrate for AIH-induced sLTF neuroplasticity.
The neuropeptide dynorphin (DYN) activates kappa opioid receptors (KORs) in the brain to produce depressive-like states and decrease motivation. KOR-mediated suppression of dopamine release in the nucleus accumbens (NAc) is considered one underlying mechanism. We previously showed that, regardless of estrous cycle stage, female rats are less sensitive than males to KOR agonist-mediated decreases in motivation to respond for brain stimulation reward, measured with intracranial self-stimulation (ICSS). However, the explicit roles of KORs, circulating gonadal hormones, and their interaction with dopamine signaling in motivated behavior are not known. As such, we measured the effects of the KOR agonist U50,488 on ICSS stimulation thresholds before and after gonadectomy (or sham surgery). We found that ovariectomized females remained less sensitive than sham or castrated males to KOR-mediated decreases in brain stimulation reward, indicating that circulating gonadal hormones do not play a role. We used qRT-PCR to examine whether sex differences in gene expression in limbic brain regions are associated with behavioral sex differences. We found no sex differences in Pdyn or Oprk1 mRNA in the NAc and ventral tegmental area (VTA), but tyrosine hydroxylase (Th) mRNA was significantly higher in female compared to male VTA. To further explore sex-differences in KOR-mediated suppression of dopamine, we used fast scan cyclic voltammetry (FSCV) and demonstrated that U50,488 was less effective in suppressing evoked NAc dopamine release in females compared to males. These data raise the possibility that females are protected from KOR-mediated decreases in motivation by an increased capacity to produce and release dopamine.
The ability of stress to trigger cocaine seeking in humans and rodents is variable and is determined by the amount and pattern of prior drug use. This study examined the role of a corticotropin releasing factor (CRF)-regulated dopaminergic projection from the ventral tegmental area (VTA) to the prelimbic cortex in shock-induced cocaine seeking and its recruitment under self-administration conditions that establish relapse vulnerability. Male rats with a history of daily long-access (LgA; 14 ☓ 6 h/d) but not short-access (ShA; 14 ☓ 2 h/d) self-administration showed robust shock-induced cocaine seeking. This was associated with a heightened shock-induced prelimbic cortex Fos response and activation of cholera toxin b retro-labeled VTA neurons that project to the prelimbic cortex. Chemogenetic inhibition of this pathway using a dual virus intersectional hM4Di DREADD (designer receptor exclusively activated by designer drug) based approach prevented shock-induced cocaine seeking. Both shock-induced reinstatement and the prelimbic cortex Fos response were prevented by bilateral intra-VTA injections of the CRF receptor 1 (CRFR1) antagonist, antalarmin. Moreover, pharmacological disconnection of the CRF-regulated dopaminergic projection to the prelimbic cortex by injection of antalarmin into the VTA in one hemisphere and the D1 receptor antagonist, SCH23390, into the prelimbic cortex of the contralateral hemisphere prevented shock-induced cocaine seeking. Finally, LgA, but not ShA, cocaine self-administration resulted in increased VTA CRFR1 mRNA levels as measured using in situ hybridization. Altogether, these findings suggest that excessive cocaine use may establish susceptibility to stress-induced relapse by recruiting CRF regulation of a stressor-responsive mesocortical dopaminergic pathway.
We showed previously that brief footshock stress and priming injections of heroin reinstate heroin-seeking after prolonged drug-free periods. Here, we examined whether the adrenal hormone, corticosterone, and brain corticotropin-releasing factor (CRF) were involved in such reinstatement. We tested the effects of adrenalectomy, chronic exposure to the corticosterone synthesis inhibitor metyrapone (100 mg/kg, s.c., twice daily), acute exposure to metyrapone, acute intracerebroventricular injections of CRF (0.3 and 1.0 microgram), and intracerebroventricular injections of the CRF antagonist alpha-helical CRF (3 and 10 micrograms). Rats were trained to self-administer heroin (100 micrograms/kg/infusion, i.v.) for 12-14 d. Extinction sessions were given for 4-8 d (saline substituted for heroin). Tests for reinstatement were given after priming injections of saline and of heroin (0.25 mg/kg, s.c.), and after intermittent footshock (15 or 30 min, 0.5 mA). Adrenalectomy (performed after training) did not affect reinstatement by heroin but appeared to potentiate the reinstatement by footshock. Chronic exposure to metyrapone (from the beginning of extinction) or an acute injection of metyrapone (3 hr before testing) did not alter the reinstatement of heroin-seeking induced by footshock or heroin. Acute exposure to metyrapone alone potently reinstated heroin-seeking. In addition, acute exposure to CRF reinstated heroin-seeking, and the CRF antagonist alpha-helical CRF attenuated stress-induced relapse. The effect of the CRF antagonist on reinstatement by heroin was less consistent. These results suggest that CRF, a major brain peptide involved in stress, contributes to relapse to heroin-seeking induced by stressors.
There is wide agreement that corticotropin-releasing hormone (CRH) systems within the brain are activated by stressful stimuli. There is also mounting evidence for the role of bombesin (BN)-like peptides in the mediation of the stress response. To date, however, the extent to which other stimuli increase the activity of these peptidergic systems has received little attention. In the present investigation we validated and used in vivo microdialysis sampling followed by ex vivo radioimmunoassays to monitor the release of CRH and BN-like peptides during appetitive (food intake) and stressful (restraint) events. It is demonstrated for the first time that the in vivo release of CRH and BN-like peptides at the central nucleus of the amygdala was markedly increased by both stressor exposure and food ingestion. In fact, the meal-elicited rise of CRH release was as great as that associated with 20 min of restraint stress. Paralleling these findings, circulating ACTH and corticosterone levels were also increased in response to both food intake and restraint. Contrary to the current views, these results indicate that either food ingestion is interpreted as a "stressful" event by certain neural circuits involving the central amygdala or that the CRH- and BN-related peptidergic systems may serve a much broader role than previously envisioned. Rather than evoking feelings of fear and anxiety, these systems may serve to draw attention to events or cues of biological significance, such as those associated with food availability as well as those posing a threat to survival.
We have shown previously that footshock stress and priming injections of cocaine reinstate cocaine seeking in rats after prolonged drug-free periods (Erb et al., 1996). Here we examined the role of brain corticotropin-releasing factor (CRF) and the adrenal hormone corticosterone in stress- and cocaine-induced reinstatement of cocaine seeking in rats. The ability of footshock stress and priming injections of cocaine to induce relapse to cocaine seeking was studied after intracerebroventricular infusions of the CRF receptor antagonist D-Phe CRF12-41, after adrenalectomy, and after adrenalectomy with corticosterone replacement. Rats were allowed to self-administer cocaine (1.0 mg/kg/infusion, i.v) for 3 hr daily for 10-14 d and were then placed on an extinction schedule during which saline was substituted for cocaine. Tests for reinstatement were given after intermittent footshock (10 min; 0.5 mA) and after priming injections of saline and cocaine (20 mg/kg, i.p.). Footshock reinstated cocaine seeking in both intact animals and animals with corticosterone replacement but not in adrenalectomized animals. The CRF receptor antagonist D-Phe CRF12-41 blocked footshock-induced reinstatement at all doses tested in both intact animals and animals with corticosterone replacement. Reinstatement by priming injections of cocaine was only minimally attenuated by adrenalectomy and by pretreatment with D-Phe CRF12-41. These data suggest that brain CRF plays a critical role in stress-induced, but only a modulatory role in cocaine-induced, reinstatement of cocaine seeking. Furthermore, the data show that although reinstatement of cocaine seeking by footshock stress requires minimal, basal, levels of corticosterone, stress-induced increases in corticosterone do not play a role in this effect.
We have shown that intracerebroventricular administration of the corticotropin-releasing factor (CRF) receptor antagonist D-Phe CRF(12-41), blocks footshock-induced reinstatement of drug seeking in cocaine-trained rats. We now report that D-Phe acts in the bed nucleus of the stria terminalis (BNST), and not in the amygdala, to block footshock-induced reinstatement of cocaine seeking. In addition, CRF injections in the BNST, and not in the amygdala, are sufficient to reinstate cocaine seeking. Rats were trained to self-administer cocaine intravenously on a fixed ratio (FR-1) schedule of reinforcement. After 5 drug-free days, animals were returned to the self-administration chambers and given daily extinction and reinstatement test sessions. To test the effects of D-Phe CRF(12-41) on stress-induced reinstatement, rats were pretreated with vehicle or D-Phe in either the BNST (10 or 50 ng per side) or amygdala (50 or 500 ng per side) before being exposed to 15 min of intermittent footshock stress. To test whether injections of CRF itself could induce reinstatement, rats were given vehicle or CRF in either the BNST (100 or 300 ng per side) or amygdala (300 ng per side) 15 min before the session. Injections of D-Phe into the BNST completely blocked footshock-induced reinstatement of cocaine seeking; injections of CRF itself in this structure induced reinstatement. Injections of these compounds into the amygdala were without effect. These findings suggest that activation of CRF receptors in the BNST, but not in the amygdala, is critical for footshock-induced reinstatement of cocaine seeking.
The goal of this article is to summarize available data examining the physiological significance of brain corticotropin-releasing factor (CRF) systems in mediating the behavioral and physiological effects of several classes of abused drugs, including opioid and psychostimulant drugs, alcohol and sedative hypnotics, nicotine, and cannabinoids. An initial discussion of CRF neurobiology is followed by consideration of the role of CRF in drug-induced activation of the hypothalamic-pituitary-adrenocortical (HPA) axis, the behavioral effects of drugs (e.g., locomotor activity, anxiogenic-like responses), drug self-administration, drug withdrawal, and relapse to drug-seeking. Subsequently, neurochemical changes in brain CRF in response to acute and chronic drug exposure are examined. A major conclusion derived from the data reviewed is that extrahypothalamic brain CRF systems are critically involved in behavioral and physiological manifestations of drug withdrawal and in relapse to drug-taking behavior induced by environmental stressors. On the other hand, it appears that hypothalamic CRF, via its action on the HPA axis, is involved in the reinforcing effects of cocaine and alcohol, and the locomotor activating effects of psychostimulant drugs. These preclinical data may provide a rationale for the development of CRF-based pharmacotherapies for the treatment of compulsive drug use in humans.
We reported previously that bilateral injection of a corticotropin-releasing factor (CRF)-receptor antagonist, D-Phe CRF(12-41), into the bed nucleus of the stria terminalis (BNST) blocks the reinstatement of cocaine seeking induced by footshock, whereas the injection of CRF into the same region induces reinstatement. One source of CRF in the BNST arises from a CRF-containing projection originating in the central nucleus of the amygdala (CeA).
To determine whether the CRF-containing projection from the amygdala to the BNST is involved in the mediation of stress-induced reinstatement of cocaine seeking by functionally interrupting the pathway.
Rats trained to self-administer cocaine (1 mg/kg, IV, 9 days) were given extinction sessions after a 10- to 11-day drug-free period, followed by tests for stress-induced reinstatement (footshock: 15 min intermittent 0.8-mA footshocks given immediately before presentation of the previously active lever). Before the tests, animals were pretreated with either: (1) TTX (2.5 ng) in amygdala (including the CeA) in one hemisphere and D-Phe CRF(12-41) (50 ng) in BNST in the other, (2) unilateral TTX, or (3) unilateral D-Phe.
Footshock reinstated cocaine seeking following unilateral injections of either TTX in amygdala or D-Phe in BNST, but following the injection of both TTX in amygdala and D-Phe in BNST the effects of footshock were greatly attenuated.
These results suggest that the CRF-containing pathway from CeA to BNST is involved in mediating the effects of CRF and its receptor antagonist in the BNST on the reinstatement of cocaine seeking.
Experiments in our laboratory have shown that central noradrenergic (NA) activation plays a major role in stress-induced reinstatement of drug seeking in rats. In the present experiments, we investigated the effects of blockade of beta-NA adrenoceptors in the bed nucleus of the stria terminalis (BNST) and in the region of the central nucleus of the amygdala (CeA) on footshock- and cocaine-induced reinstatement. Rats were trained to self-administer cocaine (0.5 mg/kg, i.v.) for 9 d and, after a 5-7 d drug-free period, were given extinction sessions followed by a test for footshock stress-induced (15 min of intermittent footshock, 0.8 mA) or cocaine-induced (20 mg/kg, i.p.) reinstatement. Before the test, different groups of rats were given bilateral infusions of one of four doses of a mixture of the beta(1)- and beta(2)-receptor antagonists betaxolol and ICI-118,551 (vehicle, 0.25, 0.5, and 1 nmol of each compound in 0.5 microliter) into either the BNST or CeA. We observed a dose-dependent reduction of stress-induced reinstatement after infusions into the BNST and a complete blockade of stress-induced reinstatement after infusions into the CeA at all doses tested. The same treatments did not block cocaine-induced reinstatement when given at either site. These data suggest that stress-induced NA activation in the BNST and in the region of the CeA is critical to relapse to drug seeking induced by stress but not to relapse induced by priming injections of cocaine, and we hypothesize that NA activity leads to activation of corticotropin-releasing factor neurons in these regions.
The serotonergic system arising from the dorsal raphe nucleus (DR) has long been implicated in psychiatric disorders, and is considered one site of action of classical anxiolytic and antidepressant agents. Recent studies implicate the DR as a site of action of novel anxiolytic and antidepressant agents that target neuropeptide systems, such as corticotropin-releasing factor (CRF) and neurokinin 1 (NK1) antagonists. The present study identified unique characteristics of the dorsomedial DR that implicate this particular subregion as a key component of a circuit, which may be targeted by these diverse psychotherapeutic agents. First, it was observed that a cluster of CRF-containing cell bodies was present in the dorsomedial DR of colchicine-treated rats. Dual-labeling immunohistochemistry revealed that almost all CRF-containing neurons were serotonergic, implicating CRF as a cotransmitter with serotonin in this subpopulation of DR neurons. Moreover, dendrites laden with immunoreactivity for NK1 had a striking topographic distribution surrounding and extending into the dorsomedial subregion of the DR, suggesting that NK1 receptor ligands may selectively impact the dorsomedial DR. Finally, anterograde tract tracing from the dorsomedial DR combined with CRF immunohistochemistry revealed that CRF-containing axons from this subregion project to CRF-containing neurons of the central nucleus of the amygdala. Taken together, the present results reveal a circuit whereby NK1 receptor activation in the dorsomedial DR can impact on limbic sources of CRF that have been implicated in emotional responses. This circuit may be relevant for understanding the mechanism of action of novel psychotherapeutic agents that act through NK1 or CRF receptors.
Footshock stress can reinstate cocaine-seeking behavior through a central action of the stress-associated neurohormone corticotropin-releasing factor (CRF). Here we report (1) that footshock stress releases CRF in the ventral tegmental area (VTA) of the rat brain, (2) that, in cocaine-experienced but not in cocaine-naive rats, this CRF acquires control over local glutamate release, (3) that CRF-induced glutamate release activates the mesocorticolimbic dopamine system, and (4) that, through this circuitry, footshock stress triggers relapse to drug seeking in cocaine-experienced animals. Thus, a long-lasting cocaine-induced neuroadaptation, presumably at the level of glutamate terminals in the VTA, appears to play an important role in stress-induced relapse to drug use. Similar neuroadaptations may be important for the comorbidity between addiction and other stress-related psychiatric disorders.
Corticotropin-releasing factor (CRF) is typically considered to mediate aversive aspects of stress, fear and anxiety. However, CRF release in the brain is also elicited by natural rewards and incentive cues, raising the possibility that some CRF systems in the brain mediate an independent function of positive incentive motivation, such as amplifying incentive salience. Here we asked whether activation of a limbic CRF subsystem magnifies the increase in positive motivation for reward elicited by incentive cues previously associated with that reward, in a way that might exacerbate cue-triggered binge pursuit of food or other incentives? We assessed the impact of CRF microinjections into the medial shell of nucleus accumbens using a pure incentive version of Pavlovian-Instrumental transfer, a measure specifically sensitive to the incentive salience of reward cues (which it separates from influences of aversive stress, stress reduction, frustration and other traditional explanations for stress-increased behavior). Rats were first trained to press one of two levers to obtain sucrose pellets, and then separately conditioned to associate a Pavlovian cue with free sucrose pellets. On test days, rats received microinjections of vehicle, CRF (250 or 500 ng/0.2 microl) or amphetamine (20 microg/0.2 microl). Lever pressing was assessed in the presence or absence of the Pavlovian cues during a half-hour test.
Microinjections of the highest dose of CRF (500 ng) or amphetamine (20 microg) selectively enhanced the ability of Pavlovian reward cues to trigger phasic peaks of increased instrumental performance for a sucrose reward, each peak lasting a minute or so before decaying after the cue. Lever pressing was not enhanced by CRF microinjections in the baseline absence of the Pavlovian cue or during the presentation without a cue, showing that the CRF enhancement could not be explained as a result of generalized motor arousal, frustration or stress, or by persistent attempts to ameliorate aversive states.
We conclude that CRF in nucleus accumbens shell amplifies positive motivation for cued rewards, in particular by magnifying incentive salience that is attributed to Pavlovian cues previously associated with those rewards. CRF-induced magnification of incentive salience provides a novel explanation as to why stress may produce cue-triggered bursts of binge eating, drug addiction relapse, or other excessive pursuits of rewards.
Footshock reinstates cocaine seeking in cocaine-experienced rats by inducing corticotropin-releasing factor (CRF) and glutamate release in the ventral tegmental area (VTA) and thus activating VTA dopaminergic neurons. Footshock-induced VTA glutamate release, dopamine activation and reinstatements are blocked by VTA administration of a alpha-helical CRF, a nonselective CRF receptor antagonist. The effects of selective CRF antagonists have not yet been reported.
The present studies were designed to explore the roles of VTA CRF receptor subtypes and CRF-BP in these effects induced by footshock.
Rats were first trained to lever-press for intravenous cocaine (1 mg/infusion/0.13 ml, FR-1 schedule), and then tested under extinction conditions until response rates returned to the pretraining baseline. Reinstatements, VTA glutamate and dopamine levels [microdialysis with high performance liquid chromatography (HPLC)] were then assessed, under various pharmacological conditions, after mild inescapable footshock.
Footshock-induced reinstatement of cocaine seeking and release of VTA glutamate and dopamine were blocked by selective blockade of VTA CRF(2) receptors (CRF(2)Rs) but not CRF(1)Rs. VTA perfusion of CRF or CRF(2)R agonists that have strong affinity for CRF-BP mimicked the effects induced by footshock while CRFR agonists that do not bind CRF-BP were ineffective. CRF(6-33), which competes for the CRF binding site on CRF-BP, attenuated the effects of CRF or urocortin I on VTA glutamate and dopamine release and on reinstatement of cocaine seeking.
The present studies revealed a role of VTA CRF-BP and suggest an involvement of CRF(2)R in the effectiveness of stress in triggering glutamate and dopamine release and cocaine seeking in drug-experienced animals.
Corticotropin-releasing factor (CRF) is a 41 amino acid peptide with potent activating effects on the pituitary adrenal axis, as shown by its ability to release adrenocorticotropin hormone and β-endorphin from the anterior pituitary (Vale et al. 1981). In accordance with such a role, a large proportion of central nervous system CRF is located within the hypothalamus (Bloom et al. 1982).
The central nucleus of the amygdala (CNA) and the parabrachial nucleus of the pons (PBN) are included within a group of brain nuclei involved in autonomic responses. Previous studies have shown that the CNA sends a considerable projection to the PBN and that both nuclei contain neurons immunoreactive to many different peptides. In the present study, we used the combined retrograde fluorescence-immunofluorescence method to determine whether the CNA projection to the PBN contains any of the following neuropeptides: corticotropin–releasing factor (CRF), neurotensin (NT), somatostatin (SS), and enkephalin (ENK). Following injections of fluorescent dye into the PBN, neurons within both lateral and medial subdivisions of the CNA were retrogradely labeled. A significant percentage of CRF (54–66%)–, NT (40–53%)–, and SS (31–50%)-immunoreactive neurons were retrogradely labeled, predominantly within the lateral CNA. Enkephalin-immunoreactive neurons were never retrogradely labeled, although they were often found adjacent to retrogradely labeled neurons. Our results show that the lateral CNA is a major source of CRF, NT, and SS terminals within the PBN. Neurons in the medial CNA also provide a significant contribution to the CNA-PBN pathway, but their chemical nature remains to be determined. We conclude that CRF, NT, and SS are important putative neurotransmitters in the CNA's regulation of PBN function. This CNA-PBN peptidergic pathway may participate in stress-related cardiovascular and respiratory responses.
Corticotropin-releasing factor (CRF), when administered directly into the CNS, can have activating properties on behaviour and can enhance behavioural responses to stress. CRF injected intraventricularly produces a dose-dependent increase in locomotor activity and increased responsiveness to an acoustic startle stimulus. However, this profile of activation changes to enhanced suppression of behaviour in stressful situations and includes increased freezing, increased conditioned suppression, increased conflict, decreased feeding and decreased behaviour in a novel open field. These effects of CRF are independent of the pituitary–adrenal axis and can be reversed by the CRF antagonist α-helical CRF(9–41). More importantly, the CRF antagonist can also reverse many behavioural responses to stressors. α-Helical CRF(9–41) reverses stress-induced fighting behaviour, stress-induced freezing, stress-induced suppression of feeding, stress-induced decreases in exploration of an elevated plus maze, fear-potentiated startle and the development of conditioned suppression. Intracerebral microinjections suggest that the amygdala may be an important site for the anti-stress effects of α-helical CRF(9–41). These results suggest that endogenous CRF systems in the CNS may have a role in mediating behavioural responses to stress and further suggest that CRF in the brain may function as a fundamental behavioural activating system. This CRF system may be particularly important in situations where an organism must mobilize not only the pituitary–adrenal system but also the CNS in response to environmental challenge.
The central administration of corticotropin-releasing hormone (CRH) to experimental animals sets into motion a coordinated series of physiological and behavioral events that promote survival during threatening situation. A large body of evidence suggest that CRH in the central nucleus of the amygdala (CEA) induces fear-related behaviors and is essential to fear conditioning; however, evidence of CRH-mediated activation of the amygdala under physiological situation is still limited. We report here a study of the impact of a psychological stressor on hypothalamic and amygdala CRH systems in the rat. Non-footshocked rats placed in a floored compartment surrounded by footshocked rats were defined as the psychological stress group. Rats were exposed to psychological stress for 15 min, and then sacrificed 1.5 and 3 h after cessation of stress. We found that our psychological stressor induced an increase in both CRH mRNA levels, as assessed by in situ hybridization histochemistry, and CRH content, as assessed by micropunch RIA, in the CEA. Exposure to the psychological stressor also caused a significant increase in CRH mRNA levels with a trend for an increase in CRH content in the dorsolateral subdivision of the bed nucleus of the stria terminalis (BNST) which is anatomically associated with the CEA. In contrast, psychological stress induced a small, but significant increase in type-1 CRH receptor (CRHR-1) mRNA in the hypothalamic paraventricular nucleus (PVN), while it failed to elevate either PVN CRH mRNA levels or content, CRH content in the median eminence (ME), or levels of plasma ACTH or corticosterone (CORT). Thus, in the context of a psychological stressor, the activation of the amygdala CRH system can occur without robust activation of the hypothalamic CRH system. In the light of previous data that the psychological stress-induced loss of sleep was reversed by the central administration of a CRH antagonist, these data suggest that CRH in the CEA may contribute to the psychological stress-evoked fear-related behavior such as hyperarousal. These data also indicate that in response to a psychological stressor, the amygdala CRH system is much more sensitive than is the CRH system emanating from the PVN.
The bed nucleus of the stria terminalis (BST) sends a dense projection to the parabrachial nucleus (PB) in the pons. The BST contains many different types of neuropeptidelike immunoreactive cells and fibers, each of which exhibits its own characteristic distribution within cytoarchitecturally distinct BST subnuclei. Corticotropin releasing factor (CRF)-, neurotensin (NT)-, somatostatin (SS)-, and enkephalin (ENK)-like immunoreactive (ir) neurons are particularly numerous within areas of the BST that project to the PB. In this study, we use the combined retrograde fluorescence-immunofluorescence method to determine whether neurons in the BST that project to the PB contain these immunoreactivities. After Fast Blue injections into PB, retrogradely labeled neurons were numerous throughout the lateral part of the BST, particularly in the dorsal lateral (DL) and posterior lateral subnuclei. Retrogradely labeled neurons were also present in the preoptic, ventral lateral, and supracapsular BST subnuclei and in the parastrial nucleus. Many of the CRF-ir, NT-ir, and SS-ir neurons in DL were retrogradely labeled. A few double-labeled cells of each type were also found in the posterior lateral, ventral lateral and supracapsular BST subnuclei ENK-ir neurons were never retrogradely labeled. Our results show that BST neurons that project to the PB stain for the same neuropeptides as those in the central nucleus of the amygdala (CeA) that project to the PB, demonstrating further the close anatomical relations between these two structures.
Corticotropin-releasing factor (CRF) is thought to have a neurotransmitter function in the mammalian central nervous system. The release of CRF into the hypothalamic-hypophyseal portal system in response to stress is known, and it has been suggested that CRF may function elsewhere in the central nervous system to promote stress-induced physiological and behavioral changes. Acute stress has been shown to activate dopamine (DA) neurons in the ventral tegmental area (VTA) that project to the prefrontal cortex. To determine whether CRF may act in the VTA to activate the mesocortical or mesolimbic DA systems, it was injected into the VTA of rats, and changes in spontaneous motor behavior and DA metabolism were measured. Intra-VTA injection of CRF produced a dose-dependent increase in horizontal and vertical photocell counts with a minimal effective dose of 0.01 and 0.1 nmol, respectively. In contrast, the minimal effective dose for CRF-stimulated motor behavior after injection into the lateral ventricles was 0.3 nmol for horizontal activity. Furthermore, in the open field, the behavioral profile of CRF (0.3 nmol) given intra-VTA differed from that observed after intraventricular injection. The motor stimulant effect of intra-VTA CRF was not blocked by pretreatment with the DA receptor antagonist haloperidol. After intra-VTA injection, CRF produced a dose-dependent decrease in DA metabolism in the prefrontal cortex. The decrease in DA metabolism in the prefrontal cortex was present at 30 and 60 min but not at 120 min after injection, and in the nucleus accumbens DA metabolism was increased only at 60 min after injection.(ABSTRACT TRUNCATED AT 250 WORDS)
Corticotropin-releasing factor (CRF) has behavioral activating effects when injected intracerebroventricularly in rats. CRF dose-dependently increased activity in a familiar photocell cage environment. This activation persisted after hypophysectomy, opiate receptor blockade, and low-dose dopamine receptor blockade, which suggests a unique mechanism of action. CRF also improved acquisition of a visual discrimination task. In aversive situations such as an open field test CRF produced behavioral changes consistent with increased emotionality. These results suggest that CRF liberated directly into the central nervous system may have a neurotropic action important for mobilizing behavioral responses to stress.
The distribution of corticotropin-releasing factor (CRF)-immunoreactive cells and fibers has been examined in the brains of normal adult rats, and in the brains of animals that had been pretreated with intraventricular injections of colchicine, or had been adrenalectomized 3-60 days before perfusion. The results suggest that CRF immunoreactivity is localized in at least three functionally distinct systems. First, most of the CRF-stained fibers in the neurohemal zone of the median eminence, which presumably modulate the release of ACTH and beta-endorphin from the pituitary, appear to arise in the paraventricular nucleus of the hypothalamus (PVH). About 2,000 CRF-stained cells are distributed throughout all eight parts of the PVH, although a majority (80%) of the cells are concentrated in the parvocellular division, and a smaller number (about 15%) are found in parts of the magnocellular division in which oxytocinergic cells predominate. This appears to be the only CRF-stained pathway in the brain that is affected (increased staining intensity) by adrenalectomy. Second, a series of cell groups in the basal telencephalon, hypothalamus, and brain stem that are known to play a role in the mediation of autonomic responses contain CRF-stained neurons. These areas, which are interconnected by stained fibers in the medial forebrain bundle and the periventricular system, include the central nucleus of the amygdala, substantia innominata, bed nucleus of the stria terminalis, medial and lateral preoptic areas, lateral hypothalamic area, central gray, laterodorsal tegmental nucleus, locus ceruleus, parabrachial nucleus, dorsal vagal complex, and regions containing the A1 and A5 catecholamine cell groups. And third, scattered CRF-stained cells are found throughout most areas of the cerebral cortex. Most such cells are confined to layers II and III in the neocortex, and their bipolar shape suggests that they are interneurons. These cells are most common in limbic regions including prefrontal areas, the cingulate gyrus, and areas bordering the rhinal fissure. Scattered immunoreactive cells are also found in dorsal parts of the dentate gyrus and Ammon's horn. These results suggest that the PVH plays a critical role in the modulation of ACTH and beta-endorphin release from the pituitary, and that CRF-containing pathways in the brain are involved in the mediation of autonomic responses.
The distribution of dopaminergic fibers in the principal components of the central extended amygdala (central amygdaloid nucleus (Ce), substantia innominata, and bed nucleus of the stria terminalis (BNST)), was studied using immunocytochemistry against tyrosine hydroxylase, dopamine beta-hydroxylase and dopamine. Dopamine fibers were found most densely distributed in the dorsolateral subdivision of the BNST and the lateral part of the Ce. Smaller numbers of dopaminergic fibers were found in the rest of the central extended amygdala. In contrast, dopamine beta-hydroxylase fibers were virtually absent from the dorsolateral bed nucleus of the stria terminalis and lateral part of the central amygdaloid nucleus, but were distributed in a moderate density in the medial part of Ce, dorsal substantia innominata and posterolateral BNST. Our results show that dopamine fibers are most concentration over those regions of the central extended amygdala with large numbers of GABAergic neurons whose projections remain within the central extended amygdala, while noradrenergic fibers are most heavily concentrated over those regions containing a large proportion of brainstem projection neurons. That dopamine fibers are concentrated over regions with GABAergic medium spiny neurons suggests that those regions might be organized as a striatal parallel.
The results of numerous studies have provided compelling evidence that CRF plays an important function in the amygdala. Stimulation of the amygdala produces physiological changes similar those observed after central injections of CRF. Central injections of CRF activate neurons in the amygdala as measured by increases in c-fos protein expression. Destruction of cells or injections of CRF antagonist in the amygdala can attenuate some of the central effects of CRF. The amygdala is the origin of major CRF-containing pathways in the brain. Amygdaloid CRF neurons project to widespread regions of the basal forebrain and brain stem. These amygdaloid pathways mainly arise from the central amygdaloid nucleus where there are a large number of CRF immunoreactive neuronal perikarya. Glucocorticoid and CRF-binding protein are located in cells of the central amygdaloid nucleus. CRF neurons in the central nucleus send their axons to the bed nucleus of the stria terminalis, lateral hypothalamus, midbrain central gray, raphe nuclei, parabrachial region, and the nucleus of the solitary tract. Tract tracing studies have suggested that amygdaloid CRF neurons also innervate CRF neurons in some of these regions and, furthermore, that CRF neurons in some of these areas project back to the CRF neurons in the amygdala. Thus, the amygdala is part of a network of brain nuclei interconnected by CRF pathways. In addition, amygdaloid CRF neurons may project directly to dopaminergic, noradrenergic, and serotonergic neurons, which have widespread projections throughout the neuroaxis.(ABSTRACT TRUNCATED AT 250 WORDS)
Corticotropin releasing factor (CRF) has been shown to initiate neuroendocrine and behavioral responses to stress. As stress and amphetamine (AMPH) show cross-sensitization, we investigated the role of endogenous CRF in behavioral sensitization to D-AMPH. In order to evaluate the participation of the central action and the pituitary-adrenocortical (PA) stimulatory effect of CRF, we compared the effects of repeated intracerebroventricular (i.c.v.) administration of CRF (0, 0.5, 2.5 micrograms/2 microliters), which have central and neuroendocrine consequences, with those of repeated subcutaneous administration of CRF (0, 0.1, 0.5, 2.5 micrograms/250 microliters), doses which only stimulate the PA axis, on the development of sensitization to AMPH-induced motor activation administered 1 week later. Repeated i.c.v. administration of CRF induced a long-lasting enhancement of the hyperactivity induced by 0.75 mg/kg peripheral administration of D-AMPH, whereas no sensitization to D-AMPH was observed following repeated subcutaneous administration of CRF. These results favor the hypothesis that a centrally mediated action of CRF is involved in the cross-sensitization of psychostimulants and stress.
Relapse is a major characteristic of drug addiction disorders and remains the primary problem for treatment. Recently, there has been hope that these disorders may be amenable to pharmacological treatments that have successfully treated other psychopathological disorders. Pharmacological approaches to drug abuse have tended to be guided by the primary drug used by the individual, though substitution has been the guiding principle in some instances, as in the case of methadone maintenance in opioid addiction. Alternatively, blockade or antagonism of the effects of the primary drug being abused has been tried, as in the case of using naltrexone to treat opioid or alcohol addiction. Though reportedly successful in some populations, it is not clear that these approaches effectively control craving for 'highs' or euphoric experiences or a return to drug use as a response to stressful life experiences. Recent experimental studies of the factors that induce craving and relapse to drug use in both humans and laboratory animals, such as drug-related cues, re-exposure to the drug itself, or exposure to stressful events, have shown that the effects of these different events are mediated by dissociable neurochemical circuitry. Another finding that emerges from these studies is that the motivation underlying drug seeking induced by events that precipitate relapse is intensified by the duration and amount of pre-exposure to a drug and the passage of time since withdrawal of the drug. One implication of such findings for the treatment of addiction is that whatever approach is taken, treatment will have to be multifaceted and maintained over an extended period of time after the initial termination of drug use.
Stress increases addictive behaviors and is a common cause of relapse. Corticotropin-releasing factor (CRF) plays a key role in the modulation of drug taking by stress. However, the mechanism by which CRF modulates neuronal activity in circuits involved in drug addiction is poorly understood. Here we show that CRF induces a potentiation of NMDAR (N-methyl-D-aspartate receptor)-mediated synaptic transmission in dopamine neurons of the ventral tegmental area (VTA). This effect involves CRF receptor 2 (CRF-R2) and activation of the phospholipase C (PLC)-protein kinase C (PKC) pathway. We also find that this potentiation requires CRF binding protein (CRF-BP). Accordingly, CRF-like peptides, which do not bind the CRF-BP with high affinity, do not potentiate NMDARs. These results provide evidence of the first specific roles for CRF-R2 and CRF-BP in the modulation of neuronal activity and suggest that NMDARs in the VTA may be a target for both drugs of abuse and stress.
Recent evidence suggests that certain stressors release both endogenous opioids and corticotropin-releasing factor (CRF) to modulate activity of the locus coeruleus (LC)-norepinephrine (NE) system. In ultrastructural studies, axon terminals containing methionine(5)-enkephalin (ENK) or CRF have been shown to target LC dendrites. These findings suggested the hypothesis that both neuropeptides may coexist in common axon terminals that are positioned to have an impact on the LC. This possibility was examined by using immunofluorescence and immunoelectron microscopic analysis of the rat LC and neighboring dorsal pontine tegmentum. Ultrastructural analysis indicated that CRF- and ENK-containing axon terminals were abundant in similar portions of the neuropil and that approximately 16% of the axon terminals containing ENK were also immunoreactive for CRF. Dually labeled terminals were more frequently encountered in the "core" of the LC vs. its extranuclear dendritic zone, which included the medial parabrachial nucleus (mPB). Triple labeling for ENK, CRF, and tyrosine hydroxylase (TH) showed convergence of opioid and CRF axon terminals with noradrenergic dendrites as well as evidence for inputs to TH-labeled dendrites from dually labeled opioid/CRF axon terminals. One potential source of ENK and CRF in the dorsal pons is the central nucleus of the amygdala (CNA). To determine the relative contribution of ENK and CRF terminals from the CNA, the CNA was electrolytically lesioned. Light-level densitometry revealed robust decreases in CRF immunoreactivity in the LC and mPB on the side ipsilateral to the lesion but little or no change in ENK immunoreactivity, confirming previous studies of the mPB. Degenerating terminals from the CNA in lesioned rats were found to be in direct contact with TH-labeled dendrites. Together, these data indicate that ENK and CRF may be colocalized to a subset of individual axon terminals in the LC "core." The finding that the CNA provides, to dendrites in the area examined, a robust CRF innervation, but little or no opioid innervation, suggests that ENK and CRF axon terminals impacting LC neurons originate from distinct sources and that terminals that colocalize ENK and CRF are not from the CNA.
Corticotropin-releasing factor (CRF)- and norepinephrine (NE)-containing neurons in the brain are activated during stress, and both have been implicated in the behavioral responses. NE neurons in the brain stem can stimulate CRF neurons in the hypothalamic paraventricular nucleus (PVN) to activate the hypothalamic-pituitary-adrenocortical axis and may affect other CRF neurons. CRF-containing neurons in the PVN, the amygdala, and other brain areas project to the area of the locus coeruleus (LC), and CRF injected into the LC alters the electrophysiologic activity of LC-NE neurons. Neurochemical studies have indicated that CRF applied intracerebroventricularly or locally activates the LC-NE system, and microdialysis and chronoamperometric measurements indicate increased NE release in LC-NE terminal fields. However, chronoamperometric studies indicated a significant delay in the increase in NE release, suggesting that the CRF input to LC-NE neurons is indirect. The reciprocal interactions between cerebral NE and CRF systems have been proposed to create a "feed-forward" loop. It has been postulated that a sensitization of such a feed-forward loop may underlie clinical depression. However, in the majority of studies, repeated or chronic stress has been shown to decrease the behavioral and the neurochemical responsivity to acute stressors. Repeated stress also seems to decrease the responsivity of LC neurons to CRF. These results do not provide support for a feed-forward hypothesis. However, a few studies using certain tasks have indicated sensitization, and some other studies have suggested that the effect of CRF may be dose dependent. Further investigations are necessary to establish the validity or otherwise of the feed-forward hypothesis.
Organisms exposed to challenging stimuli that alter the status quo inside or outside of the body are required for survival purposes to generate appropriate coping responses that counteract departures from homeostasis. Identification of an executive control mechanism within the brain capable of coordinating the multitude of endocrine, physiological, and functional coping responses has high utility for understanding the response of the organism to stressor exposure under normal or pathological conditions. The corticotropin-releasing factor (CRF)/urocortin family of neuropeptides and receptors constitutes an affective regulatory system due to the integral role it plays in controlling neural substrates of arousal, emotionality, and aversive processes. In particular, available evidence from pharmacological intervention in multiple species and phenotyping of mutant mice shows that CRF/urocortin systems mediate motor and psychic activation, stimulus avoidance, and threat recognition responses to aversive stimulus exposure. It is suggested that affective regulation is exerted by CRF/urocortin systems within the brain based upon the sensitivity of local brain sites to CRF/urocortin ligand administration and the appearance of hypothalamo-pituitary-adrenocortical activation following stressor exposure. Moreover, these same stress neuropeptides may constitute a mechanism for learning to avoid noxious stimuli by facilitating the formation of so-called emotional memories. A conceptual framework is provided for extrapolation of animal model findings to humans and for viewing CRF/urocortin activation as a continuum measure linking normal and pathological states.
Fear is an adaptive response to recognition of a potentially dangerous event. Glucocorticoids are essential for maintaining a wide variety of behavioral events by their regulation of numerous genes; one such gene encodes corticotrophin-releasing hormone (CRH). CRH is involved in diverse behavioral responses to changing environmental demands. In this review, we focus on one aspect of glucocorticoid regulation of CRH--namely, fear-related responses to diverse classes of adverse events, such as those represented by contextual and cue-specific stimuli. Three extra-hypothalamic forebrain sites appear crucial for fear-related behavioral responses: the amygdala and the bed nucleus of the stria terminalis for sustaining adaptive fear-related behaviors, and the medial prefrontal cortex for modulating fear-related behaviors. Central regulation of CRH by glucocorticoids is important for adaptive and sustained fear-related behaviors, and its aberration is associated with anxiety and depressive disorders.
A good deal is now known about the neural circuitry involved in how conditioned fear can augment a simple reflex (fear-potentiated startle). This involves visual or auditory as well as shock pathways that project via the thalamus and perirhinal or insular cortex to the basolateral amygdala (BLA). The BLA projects to the central (CeA) and medial (MeA) nuclei of the amygdala, which project indirectly to a particular part of the acoustic startle pathway in the brainstem. N-methyl-D-aspartate (NMDA) receptors, as well as various intracellular cascades in the amygdala, are critical for fear learning, which is then mediated by glutamate acting in the CeA. Less predictable stimuli, such as a long-duration bright light or a fearful context, activate the BLA, which projects to the bed nucleus of the stria terminalis (BNST), which projects to the startle pathway much as the CeA does. The anxiogenic peptide corticotropin-releasing hormone increases startle by acting directly in the BNST. CeA-mediated behaviors may represent stimulus-specific fear, whereas BNST-mediated behaviors are more akin to anxiety. NMDA receptors are also involved in extinction of conditioned fear, and both extinction in rats and exposure-based psychotherapy in humans are facilitated by an NMDA-partial agonist called D-cycloserine. ((c) 2006 APA, all rights reserved).
Stress-induced relapse to cocaine seeking: roles for the CRF(2) receptor and CRF-binding protein in the ventral tegmental area of the rat
- Wang B You
- Rice Kc Zb
- Wise
Wang B, You ZB, Rice KC, Wise RA (2007) Stress-induced relapse to cocaine seeking: roles for the CRF(2) receptor and CRF-binding protein in the ventral tegmental area of the rat. Psychopharmacol-ogy (Berl) 193:283–294.
Vector Lab-oratories) After rinsing in PB they were incubated for 10 min with 03=-diaminobenzidine (DAB) in 0.1 M PB. Sections were then incubated in DAB After rinsing the sections were mounted onto gel-coated slides, dehy-drated through a series of alcohols
- M Pb
M PB after which they were placed for 30 min in a avidin– biotin–peroxidase complex (Vectastain Elite ABC Kit, Vector Lab-oratories). After rinsing in PB they were incubated for 10 min with 0.05% 3,3=-diaminobenzidine (DAB) in 0.1 M PB. Sections were then incubated in DAB/PB with 0.01% H 2 O 2 and 8% NiCl 2. After rinsing the sections were mounted onto gel-coated slides, dehy-drated through a series of alcohols, soaked in Citrisolv (Fisher Scientific, Ottawa, CA, USA), and coverslipped with Permount (Fisher Scientific).
Amygdaloid CRF pathways
- Gray