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Abstract
The neural plasticity mechanisms that underlie learning and memory may also be engaged when drug addiction occurs. It was reported that long-lasting neuroadaptations induced by cocaine use and withdrawal require the participation of hippocampus. However, the role of corticotrophin-releasing factor receptors in this process remains unclear. In the present study, the effects of chronic cocaine treatment (a 14-day cocaine administration, 20 mg/kg i.p., daily) and short-term cocaine withdrawal (a 3-day cocaine extinction following a 14-day cocaine administration) on long-term potentiation (LTP), one prominent cellular mechanism for learning and memory, were assessed in the CA1 region of the rat hippocampal slices. We found that cocaine withdrawal, but not the chronic cocaine administration itself, significantly enhanced the magnitude of LTP in hippocampal slices, as compared with that in saline controls. Selective blockade of corticotrophin-releasing factor receptor subtype 1 (CRF(1)) with the specific antagonist NBI 27914 (100 nM in vitro) attenuated the magnitude of LTP in hippocampal slices from cocaine withdrawal rats, and intriguingly, also from saline control rats, while specific blockade of corticotrophin-releasing factor receptor subtype 2 (CRF(2)) with astressin2-B (100 nM in vitro) selectively attenuated the magnitude of LTP in hippocampal slices from cocaine withdrawal rats. Our data suggest that short-term cocaine withdrawal treatment may cause synaptic plasticity in hippocampus partially via changing the activity of CRF(2) in the hippocampus.
... Thompson et al. (2004) found that prior chronic cocaine self-administration resulted in enhanced hippocampal LTP in the CA1 subregion following 3 d of withdrawal but not following 30 d of withdrawal. In line with these results, other studies found enhanced LTP 3 d after chronic cocaine administration (Guan et al. 2009). Interestingly, Thompson et al. (2004) also found decreased hippocampal LTP 100 d after chronic cocaine self-administration, which suggests that chronic cocaine may have different short-term and long-term effects on hippocampal plasticity. ...
... In line with the results of Thompson et al. (2004) showing enhanced LTP during short-term withdrawal, Valzachi et al. (2013) found that chronic cocaine administration resulted in increased phosphorylated CREB levels in the hippocampus following 12 d of withdrawal. Therefore, there is a potential discrepancy between behavioral studies showing disrupted hippocampal learning and memory (Melnick et al. 2001; Santucci et al. 2004;Mendez et al. 2008;Santucci et al. 2008) and electrophysiology studies showing enhanced LTP with chronic cocaine administration (Thompson et al. 2002(Thompson et al. , 2004Guan et al. 2009). These contradicting results might have risen because of the fact that behavioral studies cited in this review tested their subjects in long-term withdrawal between 5 wk and 4 mo. ...
... These contradicting results might have risen because of the fact that behavioral studies cited in this review tested their subjects in long-term withdrawal between 5 wk and 4 mo. Importantly, Thompson et al. (2004) and Guan et al. (2009) showed that chronic cocaine administration enhanced LTP in short-term withdrawal (3 d), whereas disrupted LTP following long-term withdrawal (100 d). In support of this hypothesis, Del Olmo et al. (2007) found that chronic cocaine self-administration enhanced spatial learning 3 h following the last cocaine infusion. ...
It has been long hypothesized that conditioning mechanisms play major roles in addiction. Specifically, the associations between rewarding properties of drugs of abuse and the drug context can contribute to future use and facilitate the transition from initial drug use into drug-dependency. On the other hand, the self-medication hypothesis of drug abuse suggests that negative consequences of drug withdrawal result in relapse to drug use as an attempt to alleviate the negative symptoms. In this review, we explored these hypotheses and the involvement of the hippocampus in the development and maintenance of addiction to widely abused drugs such as cocaine, amphetamine, nicotine, alcohol, opiates, and cannabis. Studies suggest that initial exposure to stimulants (i.e., cocaine, nicotine, and amphetamine) and alcohol may enhance hippocampal function and therefore, the formation of augmented drug-context associations that contribute to the development of addiction. In line with the self-medication hypothesis, withdrawal from stimulants, ethanol and cannabis results in hippocampus-dependent learning and memory deficits, which suggest that an attempt to alleviate these deficits may contribute to relapse to drug use and maintenance of addiction. Interestingly, opiate withdrawal leads to enhancement of hippocampus-dependent learning and memory. Given that a conditioned aversion to drug context develops during opiate withdrawal, the cognitive enhancement in this case may result in formation of an augmented association between withdrawal induced aversion and withdrawal context. Therefore, individuals with opiate addiction may return to opiate use in order to avoid aversive symptoms triggered by the withdrawal context. Overall, the systematic examination of the role of the hippocampus in drug addiction may help to formulate a better understanding of addiction and underlying neural substrates.
... Additionally, withdrawal from repeated experimenter-delivered cocaine enhances hippocampal LTD, an effect that is blocked by application of a CRF R2 antagonist. Finally, prenatal cocaine exposure modulates hippocampal DNA methylation in newborn and adolescent rodents, altering the expression of a variety of genes (Novikova et al., 2008;Guan et al., 2009). ...
... During cocaine withdrawal, increased CRF release in limbic and stress systems is associated with enhanced anxiety-like behaviors, which can be attenuated with CRF receptor antagonists (Basso et al., 1999;Sarnyai et al., 2001). CRF R2 activity can be both anxiogenic and anxiolytic, and a CRF R2 antagonist decreases cocaine withdrawalinduced enhancement of LTP in hippocampal slices (Bale and Vale, 2004;Guan et al., 2009). We found increased expression of CRF R2 mRNA and protein in the hippocampus of cocaine-sired male offspring, with no change of CRF R1 mRNA. ...
... The hippocampus is generally considered to have a role in negative feedback on stress and anxiety following HPA activation (Herman et al., 2005;Jankord and Herman, 2008). Cocaine exposure modulates hippocampal expression and signaling of CRF and BDNF (Sarnyai et al., 1993;Yan et al., 2004;Filip et al., 2006;Guan et al., 2009). We found increased CRF R2 and tPA mRNA and protein expression and increased protein expression of proBDNF and TRkB receptor in the hippocampus of male cocaine-sired offspring. ...
Cocaine abuse and relapse remain a major public health concern in the United States and worldwide for which there is currently no approved pharmacotherapeutic intervention. Rodent cocaine self-administration, extinction, and priming-induced reinstatement can be used to model human cocaine seeking. A growing body of evidence indicates that the transport and stabilization of calcium-permeable (CP) AMPA glutamate receptors to synapses in the accumbens, a process involving CaMKII, is associated with the reinstatement of cocaine seeking. Additional evidence indicates that the dorsal striatum contributes to aspects of cocaine addiction. Moreover, relapse to cocaine abuse has been connected to elevated levels of anxiety during withdrawal and anxiolytic agents decrease the latency for animals to self-administer cocaine. A growing body of evidence indicates that environmental information can be inherited. We have previously described a cocaine-resistance phenotype in the offspring of animals that have self-administered cocaine. The enhancement of cocaine's anxiogenic effects may contribute to reduced cocaine self-administration among male cocaine-sired rats. Here, a variety of behavioral, cellular, molecular, and electrophysiological techniques are used to examine how cocaine experience directly affects the glutamatergic system in the dorsal striatum and accumbens, as well as its indirect consequences for drug-naïve offspring. Acute exposure to cocaine in drug naïve rats increased CaMKII-mediated phosphorylation of GluA1-containing AMPA receptors in the DL striatum, an effect that was not observed during cocaine priming-induced reinstatement of drug seeking. The increased phosphorylation of CaMKII and GluA1 following acute cocaine may be a compensatory mechanism in the DL striatum. Accumbens shell CP-AMPAR receptor transmission, mediated through interactions of GluA1-containing AMPARs with accessory protein SAP97, is necessary for cocaine reinstatement. Consideration of GluA1 subunit accessory proteins as potential novel targets for pharmacotherapeutic interventions in cocaine craving and addiction is warranted. Male offspring of cocaine-experienced sires exhibit baseline anxiety-like behaviors that are unaltered by subsequent cocaine exposure and dysregulation of hippocampal cellular and molecular correlates of anxiety. This identifies impairments of male offspring emotional control due to sire cocaine exposure independent of the cocaine-resistance phenotype. Collectively, these findings advance our knowledge of the direct and intergeneration effects of cocaine experience on the brain and behaviors.
... MeCP2 is involved in the functioning of mature neurons by regulating spontaneous neurotransmission and short-term synaptic plasticity (Na & Monteggia, 2011). HDAC class I family members, especially HDAC2, are recognized as major player in cognitive functions, as they cause memory impairment when over-expressed (Akhtar et al., 2009;Guan et al., 2009). DNA methylation has been studied in addiction processes, mostly for cocaine or alcohol use disorders (for reviews, see (Vaillancourt et al., 2017;). ...
... In our study, we argue that voluntary cocaine intake in rats enhanced the ECS which may be responsible for the electrophysiological changes occurring in HPC following cocaine intake. Indeed, chronic cocaine (either cocaine-SA or i.p) enhanced LTP in the HPC after a short withdrawal (Thompson et al., 2004;Guan et al., 2009). Interestingly, the ECS is described as a hippocampal network administrator as this system regulates HPC synchronized activity (Lupica et al., 2017). ...
Occidental countries currently face an epidemic of obesity and related diseases. As eating disorders and drug addiction are both complex pathologies inducing long-term neuroadaptations, we investigated common alterations induced by either sugar or cocaine intake in reward-related brain regions. We focused our research on the endocannabinoid and opioid systems, as both systems are expressed in the central nervous system and play a crucial role in drug reward and food intake. Overall, our results highlight the hippocampus as a highly involved brain site following cocaine use. Moreover, our work sheds light on epigenetic mechanisms regulating the endocannabinoid system. More importantly, we demonstrate that a binge-like intake of sucrose induced similar transcriptional adaptations to that of voluntary cocaine intake in the nucleus accumbens. These findings may pave the way to new therapeutic targets for addictive behaviors.
... For example, CRF-related peptides were shown to enhance LTP after cocaine withdrawal Fu et al. 2007;Krishnan et al. 2010). Our previous work showed that both CRF 1 and CRF 2 receptors are involved in enhanced LTP during cocaine withdrawal in the hippocampus (Guan et al. 2009). These findings suggest that CRF-related peptides and their receptors may play an important role in relapse at least in part by modulating synaptic plasticity in key brain circuits involved in learning and memory. ...
... Blockade of CRF 1 , but not CRF 2 , normalized drug withdrawal-impaired synaptic activity in the juxtacapsular bed nucleus of the stria terminalis (Francesconi et al. 2009). However, we recently showed that specific blockade of CRF 2 significantly attenuated cocaine withdrawal-induced enhancement of LTP in the hippocampus without affecting the formation of LTP under normal conditions (Guan et al. 2009). Here, CRF-induced enhancement of corticostriatal LTP in the cocaine-withdrawal group was also attenuated by a CRF 2 -selective antagonist. ...
J. Neurochem. (2010) 115, 795–803.
The roles of two subtypes of corticotrophin-releasing factor (CRF) receptor in corticostriatal synaptic plasticity under cocaine withdrawal condition were examined in this study. Neither the resting membrane potential and input resistance of striatal neurons nor the long-term potentiation (LTP) of corticostriatal slices were affected by cocaine withdrawal. CRF dose-dependently enhanced in vitro corticostriatal LTP in rats from both cocaine-withdrawal and saline-control groups. Yet, the enhancement of corticostriatal LTP by CRF (20, 40, 80 nM) was significantly greater in the cocaine-withdrawal group than in the control group. CRF1-selective antagonist (NBI 27914, 100 nM) attenuated the CRF-induced enhancement of corticostriatal LTP in both groups, whereas the CRF2-selective antagonist (astression2B, 100 nM) attenuated the enhanced corticostriatal LTP only in the cocaine-withdrawal group. Importantly, urocortin2 (a CRF2-selective agonist, 40 nM) selectively increased corticostriatal LTP in the cocaine-withdrawal group, but not in the saline controls. The urocortin2-induced enhancement of LTP was totally blocked by astression2B (100 nM). These results suggest that the CRF system modulate neuroadaptive changes in the corticostriatal circuit during cocaine withdrawal, and the CRF2 in this area mediate an important mechanism that contributes to the relapse of cocaine addiction.
... A detailed overview of alterations in CRF signaling that emerge with chronic drug exposure is beyond the scope of this review. However, changes in CRF signaling in a variety of brain regions including the amygdala (see e.g., [97,[224][225][226][227][228][229][230][231][232]), hippocampus (see e.g., [233]), BNST (see e.g., [85,[234][235][236]), septum (see e.g., [237]), prefrontal cortex (see e.g., [238]), nucleus accumbens (see e.g., [239,240]), serotonergic raphe nuclei (see e.g., [241][242][243]), noradrenergic cell groups (see e.g., [244,245]), and VTA [88,119,120,[246][247][248] have been demonstrated. The functional consequences of altered CRF signaling likely extend beyond dysphoric effects and may include CRF-dependent alterations in decision making [249], reward conditioning [250], drug memory reconsolidation [156] and cognition [251]. ...
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.
... Much research has focused on drug-induced adaptations within frontostriatal circuits, and both facilitated dorsal striatal (DSTR) and impaired prefrontal cortical (PFC) plasticity/function have been largely implicated in the cognitive and behavioral abnormalities associated with excessive exposure to psychostimulants and relapse (Belin & Everitt, 2008;Chen et al., 2013;Fuchs, Branham, & See, 2006;LeBlanc, Maidment, & Ostlund, 2013;Lucantonio, Stalnaker, Shaham, Niv, & Schoenbaum, 2012;Moratalla, Elibol, Vallejo, & Graybiel, 1996;Vanderschuren, Di Ciano, & Everitt, 2005;Volkow et al., 2006). However, additional evidence has shown that repeated cocaine exposure impairs HPC-dependent learning and HPC longterm potentiation (LTP) is enhanced or diminished depending on the length of cocaine abstinence, short versus long, respectively (Beveridge, Smith, Daunais, Nader, & Porrino, 2006;Briand, Gross, & Robinson, 2008;Guan, Zhang, Xu, & Li, 2009;Kutlu & Gould, 2016;Mendez et al., 2008;Sudai et al., 2011;Thompson, Swant, Gosnell, & Wagner, 2004). Whether impairments in HPC memory processing and plasticity contribute to the predominant use of DLS-dependent learning strategies following repeated cocaine exposure has not been well studied and the neuroadaptations supporting psychostimulant-mediated transitions in behavioral learning remain poorly understood. ...
The transition from recreational drug use to addiction involves pathological learning processes that support a persistent shift from flexible, goal‐directed to habit behavioral control. Here, we examined the molecular mechanisms supporting altered function in hippocampal (HPC) and dorsolateral striatum (DLS) memory systems following abstinence from repeated cocaine. After 3 weeks of cocaine abstinence (experimenter‐ or self‐administered), we tested new behavioral learning in male rats using a dual‐solution maze task, which provides an unbiased approach to assess HPC‐ versus DLS‐dependent learning strategies. Dorsal hippocampus (dHPC) and DLS brain tissues were collected after memory testing to identify transcriptional adaptations associated with cocaine‐induced shifts in behavioral learning. Our results demonstrate that following prolonged cocaine abstinence rats show a bias toward the use of an inflexible, habit memory system (DLS) in lieu of a more flexible, easily updated memory system involving the HPC. This memory system bias was associated with upregulation and downregulation of brain‐derived neurotrophic factor (BDNF) gene expression and transcriptionally permissive histone acetylation (acetylated histone H3, AcH3) in the DLS and dHPC, respectively. Using viral‐mediated gene transfer, we overexpressed BDNF in the dHPC during cocaine abstinence and new maze learning. This manipulation restored HPC‐dependent behavioral control. These findings provide a system‐level understanding of altered plasticity and behavioral learning following cocaine abstinence and inform mechanisms mediating the organization of learning and memory more broadly.
... Although we did not observe significant changes of the LTP pathway in the alcoholics, the phosphatidylinositol signaling system, which is closely related to the LTP pathway, was significantly altered by chronic exposure to both cocaine and alcohol. These findings of gene expression changes, together with other studies that have shown the effects of cocaine on LTP (del Olmo et al., 2006;Dunwiddie, Proctor, & Tyma, 1988;Guan, Zhang, Xu, & Li, 2009;Huang, Lin, & Hsu, 2007;Smith, Browning, & Dunwiddie, 1993;Thompson, Gosnell, & Wagner, 2002;Thompson, Swant, & Wagner, 2005), provide evidence that chronic exposure to cocaine, and possibly alcohol, leads to long-term changes in the plasticity of the hippocampus and underlines the importance in addiction of molecular mechanisms for learning. ...
Addiction is due to changes in the structure and function of the brain, including neuronal networks and the cells that comprise them. Within cells, gene expression changes can track and help explain their altered function. Transcriptional changes induced by addictive agents are dynamic and divergent and range from signal pathway-specific perturbations to widespread molecular and cellular dysregulation that can be measured by "omic" methods and that can be used to identify new pathways. The molecular effects of addiction depend on timing of exposure or withdrawal, the stage of adaptation, the brain region, and the behavioral model, there being many models of addiction. However, the molecular neural adaptations across different drug exposures, conditions, and regions are to some extent shared and can reflect common actions on pathways relevant to addiction. Epigenetic studies of DNA methylation and histone modifications and studies of regulatory RNA networks have been informative for elucidating the mechanisms of transcriptional change in the addicted brain.
... Indeed, the local infusion of CRF into the PFC potentiates the cocaine-induced decrease in neuronal firing (Orozco-Cabal et al., 2008). Moreover, a CRF 2 receptor-preferring antagonist attenuates the increased hippocampal long-term potentiation observed during a short-term (3 d) cocaine withdrawal (Guan et al., 2009). However, CRF role in neuronal electrophysiological changes following long-term cocaine withdrawal remains poorly understood. ...
Psychostimulant drug abuse, dependence and withdrawal are associated with cognitive dysfunction and impact stress-sensitive systems. The corticotropin-releasing factor (CRF) system orchestrates stress responses via CRF1 and CRF2 receptors and is implicated in substance use disorders. However, CRF2 role in psychostimulant drug-induced cognitive dysfunction remains to be elucidated. In the present study, wild-type and CRF2-/- mice are injected with cocaine and memory assessed by the novel object recognition (NOR) task throughout relatively long periods of drug withdrawal. Following recovery from the drug-induced memory deficits, the mice are stressed prior to the NOR task and brain gene expression evaluated by in situ hybridization. Cocaine impairs NOR memory in wild-type and CRF2-/- mice. However, following cocaine withdrawal NOR memory deficits last less time in CRF2-/- than in wild-type mice. Furthermore, a relatively mild stressor induces the re-emergence of NOR deficits in long-term cocaine-withdrawn wild-type but not CRF2-/- mice. Cocaine-withdrawn mice show a genotype-independent higher c-fos expression in the NOR memory-relevant perirhinal cortex than drug-naïve mice. However neither genotype nor drug withdrawal affect the expression of tyrosine hydroxylase in the ventral tegmental area or the locus coeruleus and CRF in the central nucleus of the amygdala or the paraventricular nucleus of the hypothalamus, brain regions implicated in stress and drug responses. These data indicate a new role for the CRF2 receptor in cognitive deficits induced by cocaine withdrawal, both as regards to their duration and their re-induction by stress. Interestingly, prototypical brain stress systems other than CRF do not appear to be involved.
... As in other brain areas, in vivo exposure to drugs such as cocaine enhances hippocampal LTP (Thompson et al. 2002(Thompson et al. , 2004Del Olmo et al. 2006b;Guan et al. 2009;Perez et al. 2010), gene expression (Freeman et al. 2001;Ary and Szumlinski 2007;Krasnova et al. 2008;Perrotti et al. 2008;Tropea et al. 2008), and synaptic growth (Fole et al. 2011). The drugs also enhance synaptic transmission and/or LTP in vitro, in some cases through activation of D1 receptors (Del Olmo et al. 2006a;Stramiello and Wagner 2010;Swant et al. 2010). ...
Recent studies in Aplysia have identified a new variation of synaptic plasticity in which modulatory transmitters enhance spontaneous release of glutamate, which then acts on postsynaptic receptors to recruit mechanisms of intermediate- and long-term plasticity. In this review I suggest the hypothesis that similar plasticity occurs in mammals, where it may contribute to reward, memory, and their dysfunctions in several psychiatric disorders. In Aplysia, spontaneous release is enhanced by activation of presynaptic serotonin receptors, but presynaptic D1 dopamine receptors or nicotinic acetylcholine receptors could play a similar role in mammals. Those receptors enhance spontaneous release of glutamate in hippocampus, entorhinal cortex, prefrontal cortex, ventral tegmental area, and nucleus accumbens. In all of those brain areas, glutamate can activate postsynaptic receptors to elevate Ca(2+) and engage mechanisms of early-phase long-term potentiation (LTP), including AMPA receptor insertion, and of late-phase LTP, including protein synthesis and growth. Thus, presynaptic receptors and spontaneous release may contribute to postsynaptic mechanisms of plasticity in brain regions involved in reward and memory, and could play roles in disorders that affect plasticity in those regions, including addiction, Alzheimer's disease, schizophrenia, and attention deficit hyperactivity disorder (ADHD).
... These findings are supported by previous reports that methamphetamine can cause longlasting changes in neuronal systems (Cadet, 2001(Cadet, , 2005 and alter synaptic plasticity (Kauer and Malenka, 2007;Thompson et al., 2002). There have been a number of reports on the effects of cocaine on hippocampal synaptic transmission (Del Olmo et al., 2006a,b;Guan et al., 2009;Thompson et al., 2004), and there are some reports showing that METH alters synaptic transmission in the striatum (Nishioku et al., 1999) and hippocampus (Onaivi et al., 2002;Swant et al., 2010). In this study, the pairedpulse facilitation (PPF) protocol consisted of two pulses at baseline intensity separated by 50 ms, followed by baseline stimulation, and three 100 Hz pulses with a 30-s interstimulus interval for LTP induction. ...
Methamphetamine (METH) is a highly addictive and neurotoxic psychostimulant. Its use in humans is often associated with neurocognitive impairment. Whether this is due to long-term deficits in short-term memory and/or hippocampal plasticity remains unclear. Recently, we reported that METH increases baseline synaptic transmission and reduces LTP in an ex-vivo preparation of the hippocampal CA1 region from young mice. In the current study, we tested the hypothesis that a repeated neurotoxic regimen of METH exposure in adolescent mice decreases hippocampal synaptic plasticity and produces a deficit in short-term memory. Contrary to our prediction, there was no change in the hippocampal plasticity or short-term memory when measured after 14 days ofMETH exposure. However, we found that at 7, 14, and 21 days of drug abstinence, METH-exposed mice exhibited a deficit in spatial memory, which was accompanied by a decrease in hippocampal plasticity. Our results support the interpretation that the deleterious cognitive consequences of neurotoxic levels of METH exposure may manifest and persist after drug abstinence. Therefore, therapeutic strategies should consider short-term as well as long-term consequences of methamphetamine exposure. Synapse, 2012. © 2012 Wiley Periodicals, Inc.
... In rodents, withdrawal from chronic cocaine is generally accompanied by changes in expression of genes involved in synaptic plasticity (see Freeman et al., 2010 for whole genome expression analysis in cocaine-abstinent rat). Cocaine withdrawal-induced changes in neuroplasticity is evidenced by the enhancement of long term potentiation (LTP) in hippocampal slices from rats withdrawn from chronic cocaine (Guan et al., 2009). Interestingly, the deficit in hippocampal cell proliferation reflected in a reduction of the number of BrdU-positive cells following chronic cocaine administration was reduced after 2-wks of withdrawal from cocaine, returning to normal levels 3-4 weeks post-withdrawal (Noonan et al., 2008;Xie et al., 2009). ...
This review discusses recent research of mood disorders associated with the cessation of psychoactive substances, with an emphasis on preclinical studies that have been published in the last decade. Animal models exhibiting anhedonic and depressive-like behaviours associated with drug withdrawal have been used to study the neurobiology of mood disorders and have culminated in the identification of novel targets for the treatment of depressive-like symptoms. This review will introduce the behavioural as well as the neurochemical and plasticity changes in depressed patients and several animal models of depression. Following, we provide a more in-depth discussion of the role of serotonergic neurotransmission and Hypothalamic-Pituitary-Adrenal (HPA) axis regulation as well as the neurogenic changes occurring after chronic drug intake focusing on the withdrawal associated depression. Although we mainly focus on animal data, some relevant human studies are also discussed. Establishing the commonalities of depression and drug-seeking behaviour will allow us to elucidate the factors driving the high co-morbidity between mood disorders and drug dependence.
... This finding is consistent with a report by Wang et al. (2005), who found that while footshock-induced increases in VTA CRF were observed in the VTA, the ability of CRF to regulate dopamine and glutamate levels in the VTA required a history of cocaine self-administration. The apparent augmentation of CRF responsiveness is also consistent with reports that CRF responsiveness in a number of brain regions is heightened following repeated cocaine administration (Liu et al., 2005;Guan et al., 2009;Orozco-Cabal et al., 2008;Erb et al., 2005;Pollandt et al., 2006;Francesconi et al., 2009). Although the effects of LgA cocaine self-administration on CRF-R1 receptor-mediated actions in the VTA have not been examined, some insight into potential mechanisms underlying heightened CRF regulation of cocaine seeking can be provided by studies involving repeated experimenter-delivered cocaine. ...
Stressful events are determinants of relapse in recovering cocaine addicts. Excessive cocaine use may increase susceptibility to stressor-induced relapse through alterations in brain corticotropin-releasing factor (CRF) regulation of neurocircuitry involved in drug seeking. We previously reported that the reinstatement of cocaine seeking by a stressor (footshock) is CRF dependent and is augmented in rats that self-administered cocaine under long-access (LgA; 6 h daily) conditions for 14 d when compared with rats provided shorter daily cocaine access [short access (ShA) rats; 2 h daily]. Further, we have demonstrated that reinstatement in response to intracerebroventricular CRF administration is heightened in LgA rats. This study examined the role of altered ventral tegmental area (VTA) responsiveness to CRF in intake-dependent increases in CRF- and stress-induced cocaine seeking. Bilateral intra-VTA administration of CRF (250 or 500 ng/side) produced reinstatement in LgA but not ShA rats. In LgA rats, intra-VTA CRF-induced reinstatement was blocked by administration of the CRF-receptor type 1 (CRF-R1) antagonist antalarmin (500 ng/side) or CP-376395 (500 ng/side), but not the CRF-R2 antagonist astressin-2B (500 ng or 1 μg/side) or antisauvagine-30 (ASV-30; 500 ng/side) into the VTA. Likewise, intra-VTA antalarmin, but not astressin-2B, blocked footshock-induced reinstatement in LgA rats. By contrast, neither intra-VTA antalarmin nor CP-376395 altered food-reinforced lever pressing. Intra-VTA injection of the CRF-R1-selective agonist cortagine (100 ng/side) but not the CRF-R2-selective agonist rat urocortin II (rUCN II; 250 ng/side) produced reinstatement. These findings reveal that excessive cocaine use increases susceptibility to stressor-induced relapse in part by augmenting CRF-R1-dependent regulation of addiction-related neurocircuitry in the VTA.
... Repeated cocaine administration causes plasticity at glutamatergic synapses in the NAc that is expressed as changes in glutamate receptor surface expression, density of dendritic spines and synaptic function (Zhang et al., 1998; Robinson et al., 2001; Li et al., 2004; Boudreau and Wolf, 2005; Martin et al., 2006; Kourrich et al., 2007; Huang et al., 2009; Kourrich and Thomas, 2009; Moussawi et al., 2009). Many of these changes only develop several weeks after the final cocaine exposure, suggesting that abstinence is an important mediator of the plasticity (Robinson et al., 2001; Li et al., 2004; Boudreau and Wolf, 2005; Boudreau et al., 2007; Kourrich et al., 2007; Guan et al., 2009). These observations raised the possibility that withdrawal itself might be the trigger for the reported functional and morphological changes in the NAc. ...
Cocaine induces plasticity at glutamatergic synapses in the nucleus accumbens (NAc). Withdrawal was suggested to play an important role in the development of this plasticity by studies showing that some changes only appear several weeks after the final cocaine exposure. In this study, the requirement for prolonged withdrawal was evaluated by comparing the changes in glutamatergic transmission induced by two different noncontingent cocaine treatments: a short treatment followed by prolonged withdrawal, and a longer treatment without prolonged withdrawal. Recordings were performed from mouse medium spiny neurons (MSNs) in the NAc at the same time after the first cocaine injection under both treatments. A similar increase in the frequency of glutamate-mediated miniature EPSCs was observed in D(1)-expressing MSNs after both cocaine treatments, demonstrating that prolonged withdrawal was not required. Furthermore, larger AMPA receptor-to-NMDA receptor ratios, higher spine density, and enlarged spine heads were observed in the absence of withdrawal after a long cocaine treatment. These synaptic adaptations expressed in D(1)-containing MSNs of the NAc core were not further enhanced by protracted withdrawal. In conclusion, a few repeated cocaine injections are enough to trigger adaptations at glutamatergic synapses in D(1)-expressing MSNs, which, although they take time to develop, do not require prolonged cocaine withdrawal.
... Drugs of abuse, including METH, can cause long-lasting changes in neuronal systems [27,28], and alter synaptic plasticity [29,30]. There have been a number of reports on the effects of cocaine on hippocampal synaptic transmission [24,31,32,33, 34,35], and although there are some reports concerning the effects of METH on synaptic transmission in the striatum [36] and hippocampus [37], the specific nature and pharmacology of METH-evoked changes in hippocampal plasticity are ill-defined. Here we examined the systemic and acute effects of METH on baseline synaptic transmission and long-term potentiation (LTP) in the CA1 region of the hippocampus. ...
Methamphetamine (METH) is an addictive psychostimulant whose societal impact is on the rise. Emerging evidence suggests that psychostimulants alter synaptic plasticity in the brain--which may partly account for their adverse effects. While it is known that METH increases the extracellular concentration of monoamines dopamine, serotonin, and norepinephrine, it is not clear how METH alters glutamatergic transmission. Within this context, the aim of the present study was to investigate the effects of acute and systemic METH on basal synaptic transmission and long-term potentiation (LTP; an activity-induced increase in synaptic efficacy) in CA1 sub-field in the hippocampus. Both the acute ex vivo application of METH to hippocampal slices and systemic administration of METH decreased LTP. Interestingly, the acute ex vivo application of METH at a concentration of 30 or 60 microM increased baseline synaptic transmission as well as decreased LTP. Pretreatment with eticlopride (D2-like receptor antagonist) did not alter the effects of METH on synaptic transmission or LTP. In contrast, pretreatment with D1/D5 dopamine receptor antagonist SCH23390 or 5-HT1A receptor antagonist NAN-190 abrogated the effect of METH on synaptic transmission. Furthermore, METH did not increase baseline synaptic transmission in D1 dopamine receptor haploinsufficient mice. Our findings suggest that METH affects excitatory synaptic transmission via activation of dopamine and serotonin receptor systems in the hippocampus. This modulation may contribute to synaptic maladaption induced by METH addiction and/or METH-mediated cognitive dysfunction.
... Withdrawal-induced enhanced long-term potentiation in hippocampal slices associated with chronic high-dose cocaine exposure was blocked by both CRF 1 and CRF 2 receptor antagonists ( Guan et al., 2009). In brain slice recordings from the lateral septum following acute withdrawal from chronic cocaine, a shift in CRF 2 receptor activity from inhibition to facilitation was observed ( Liu et al., 2005). ...
Drug addiction is a chronically relapsing disorder characterized by a compulsion to seek and take drugs, the development of dependence, and the manifestation of a negative emotional state when the drug is removed. Activation of brain stress systems is hypothesized to be a key element of the negative emotional state produced by dependence that drives drug-seeking through negative reinforcement mechanisms, defined as the "dark side" of addiction. The focus of the present review is on the role of corticotropin-releasing factor (CRF) and CRF-related peptides in the dark side of addiction. CRF is a key mediator of the hormonal, autonomic, and behavior responses to stressors. Emphasis is placed on the role of CRF in extrahypothalamic systems in the extended amygdala, including the central nucleus of the amygdala, bed nucleus of the stria terminalis, and a transition area in the shell of the nucleus accumbens, in the dark side of addiction. The urocortin/CRF(2) systems have been less explored, but results suggest their role in the neuroadaptation associated with chronic drug use, sometimes in opposition to the effects produced by the CRF(1) receptor. Compelling evidence argues that the CRF stress system, including its activation of the hypothalamic-pituitary-adrenal axis, plays a key role in engaging the transition to dependence and maintaining dependence once it is initiated. Understanding the role of the CRF systems in addiction not only provides insight into the neurobiology of the dark side of addiction, but also provides novel targets for identifying vulnerability to addiction and the treatment of addiction.
Cocaine use disorder (CUD) is a significant public health issue that generates substantial personal, familial, and economic burdens. Still, there are no FDA-approved pharmacotherapies for CUD. Cocaine-dependent individuals report anxiety during withdrawal, and alleviation of anxiety and other negative affective states may be critical for maintaining drug abstinence. However, the neurobiological mechanisms underlying abstinence-related anxiety in humans or anxiety-like behavior in rodents are not fully understood. This review summarizes investigations regarding anxiety-like behavior in mice and rats undergoing cocaine abstinence, as assessed using four of the most common anxiety-related assays: the elevated plus (or its derivative, the elevated zero) maze, open field test, light-dark transition test, and defensive burying task. We first summarize available evidence that cocaine abstinence generates anxiety-like behavior that persists throughout protracted abstinence. Then, we examine investigations concerning neuropeptide, neurotransmitter, and neuromodulator systems in cocaine abstinence-induced anxiety-like behavior. Throughout, we discuss how differences in sex, rodent strain, cocaine dose and dosing strategy, and abstinence duration interact to generate anxiety-like behavior.
Background:
Nicotine addiction supports tobacco smoking, a main preventable cause of disease and death in Western countries. It develops through long-term neuroadaptations in the brain reward circuit by modulating intracellular pathways and regulating gene expression. This study assesses the regional expression of the transcripts of the CRF transmission in a nicotine sensitization model, since it is hypothesised that the molecular neuroadaptations that mediate the development of sensitization contribute to the development of addiction.
Methods:
Rats received intraperitoneal nicotine administrations (0.4 mg/kg) once daily for either 1 day or over 5 days. Locomotor activity was assessed to evaluate the development of sensitization. The mRNA expression of CRF and CRF1 and CRF2 receptors was measured by qPCR in the ventral mesencephalon, ventral striatum, dorsal striatum (DS), prefrontal cortex (PFCx), and hippocampus (Hip).
Results:
Acute nicotine administration increased locomotor activity in rats. In the sub-chronic group, locomotor activity progressively increased and reached a clear sensitization. Significant effects of sensitization on CRF mRNA levels were detected in the DS (increasing effect). Significantly higher CRF1 and CRF2 receptor levels after sensitization were detected in the Hip. Additionally, CRF2 receptor levels were augmented by sensitization in the PFCx, and treatment and time-induced increases were detected in the DS. Nicotine treatment effects were observed on CRF1R levels in the DS.
Conclusions:
This study suggests that the CRF transmission, in addition to its role in increasing withdrawal-related anxiety, may be involved in the development of nicotine-habituated behaviours through reduced control of impulses and the aberrant memory plasticity characterising addiction.
Several areas of the hippocampal formation receive dopaminergic innervation from the ventral tegmental area and substantia nigra pars compacta and thus contain synapses where cocaine can exert its pharmacological effects. Here, we review recent findings indicating that cocaine exposure elicits increases in dopamine neurotransmission within the hippocampal formation and produces prolonged hippocampal neuroplasticity, at least in part via D1-like dopamine receptor-dependent mechanisms. In turn, cocaine-induced hippocampal neuroplasticity augments dopamine release and D1-like receptor stimulation in brain regions where hippocampal and dopaminergic axons coterminate and alters dopamine neuronal activity via feedback to the midbrain. The septal and temporal subdivisions of the hippocampal formation differ in dopaminergic innervation and extrahippocampal connectivity and play complementary roles in phenomena related to cocaine addiction. Specifically, D1-like receptor stimulation in the septal hippocampal formation controls cocaine-associated contextual learning and memory, while the temporal hippocampal formation modulates dopamine neurotransmission to encode cocaine reward and reinforcement as well as the motivational effects of cocaine-associated environmental stimuli.
Stimulant-related disorders are characterized by emotional-like, cognitive and social dysfunction that may contribute to the maintenance of the disease. In addition, stimulant use and withdrawal may alter brain stress systems. The corticotropin-releasing factor (CRF) system is a major stress coordinator hypothesized to contribute to substance-related disorders. CRF signalling is mediated by two receptor types, named CRF1 and CRF2. The specific role of each of the CRF receptors in negative affective-like, cognitive and social dysfunction associated with stimulant administration and withdrawal remains largely unknown. The present study demonstrates that the CRF1 receptor-deficiency increases the anxiety-like behaviour induced by intermittent administration of escalating doses of cocaine (5-20 mg/kg, i.p.), as assessed by the elevated plus maze. In addition, the same cocaine regimen induces novel object recognition (NOR) and sociability deficits, which are unaffected by CRF2 receptor-deficiency. However, CRF2 receptor-deficiency effectively shortens the duration of the NOR and sociability deficit induced by cocaine withdrawal. Furthermore, following the apparent recovery of NOR and sociability performances during relative long-term (42 days) cocaine withdrawal, CRF2 receptor-deficiency eliminates the stress-induced re-emergence of NOR and sociability deficit. Stressed cocaine-withdrawn mice show a genotype-independent higher c-fos mRNA expression in the perirhinal cortex, a brain region mediating NOR performance, than stressed drug-naïve mice. However, neither genotype nor drug withdrawal affects the expression of tyrosine hydroxylase in the ventral tegmentale area and the locus coeruleus, CRF in the amygdala and the paraventricular nucleus of the hypothalamus and dynorphin in the nucleus accumbens shell. The latter results suggest that stress vulnerability during long-term cocaine withdrawal is not due to alterations in stress-coping mechanisms. The present study provides initial evidence of a critical role for the CRF system in cognitive and sociability deficits and vulnerability induced by stimulant administration and withdrawal, suggesting new therapeutic strategies for substance-related disorders.
Here we explored the in vivo role of brain corticotropin-releasing factor receptor type-2 (CRFR2) in cocaine-primed reinstatement of drug seeking. Conditioned place preference (CPP) procedure was used to assess the acquisition, extinction and reinstatement of cocaine-seeking behavior in rats. First, expressions of CRFR2 were shown to be affected in a brain region-specific manner within cocaine-induced CPP and cocaine-extinct CPP models. Bilateral blockade of CRFR2 in the dorsal portion of the medial prefrontal cortex (mPFC), or hippocampus (HP) was partially inhibited, but in the dorsal striatum (DS) did not affect, the cocaine-primed reinstatement of cocaine CPP.
Understanding the neurobiological processes that contribute to the establishment and expression of stress-induced regulation of cocaine use in addicted individuals is important for the development of new and better treatment approaches. It has been previously shown that rats self-administering cocaine under long-access conditions (6 h daily) display heightened susceptibility to the reinstatement of extinguished cocaine seeking by a stressor, electric footshock, or i.c.v. administration of the stressor-responsive neuropeptide, corticotropin-releasing factor (CRF). This study tested the hypothesis that adrenal responsiveness during earlier long-access cocaine self-administration (SA) is necessary for the establishment of later CRF-dependent stress-induced reinstatement. Reinstatement by footshock, but not a cocaine challenge (10 mg/kg, i.p.) following long-access SA, was blocked by i.c.v. administration of the CRF receptor antagonist, α-helical CRF(9-41) (10 μg). Elimination of SA-induced adrenal responses through surgical adrenalectomy and diurnal corticosterone replacement (ADX/C) before 14 days of SA under long-access conditions had minimal impact on cocaine SA, but blocked later footshock-induced reinstatement. By contrast, ADX/C after SA, but before extinction and reinstatement testing, failed to reduce footshock-induced reinstatement. Likewise, ADX/C before 14 days long-access SA prevented later reinstatement by i.c.v. CRF (0.5 or 1.0 μg). However, significant CRF-induced reinstatement was observed when rats underwent ADX/C following SA, but before extinction and reinstatement testing, although a modest but statistically nonsignificant reduction in sensitivity to CRF's reinstating effects was observed. Taken together, these findings suggest that adrenal-dependent neuroadaptations in CRF responsiveness underlie the increased susceptibility to stress-induced relapse that emerges with repeated cocaine use.
Evidence suggests that the noradrenergic and corticotrophin-releasing factor (CRF) systems play critical roles in relapse and stress-related behaviors. In particular, behavioral studies point to a serial signaling process initiated by β-adrenergic receptors that requires CRF receptor (CRFR)-dependent signaling in the bed nucleus of the stria terminalis (BNST) to produce stress-induced relapse to cocaine seeking.
We used whole cell patch clamp recordings from acutely prepared mouse brain slices to examine the actions of β-adrenergic receptors and CRFR1 on excitatory transmission in BNST. We examined the effects of agonists of these receptors in slices prepared from naive, sham, and cocaine-conditioned mice.
β(1)-adrenergic receptor activation within the BNST produces an enhancement of excitatory synaptic transmission that requires CRFR1-dependent signaling. We show that chronic cocaine administration transiently disrupts β(1)-adrenergic- and CRFR1-dependent enhancement of glutamatergic transmission, that this disruption wanes with time, and that it can be reintroduced with a cocaine challenge.
In total, these studies identify a circuit mechanism within the BNST that may play an important role in CRF- and norepinephrine-regulated behaviors.
Role of cocaine in influencing blood-brain barrier (BBB) function is still unknown. Available evidences suggest that cocaine administration results in acute hyperthermia and alterations in brain serotonin metabolism. Since hyperthermia is capable to induce the breakdown of the BBB either directly or through altered serotonin metabolism, a possibility exists that cocaine may induce neurotoxicity by causing BBB disruption. This hypothesis is discussed in this review largely based on our own laboratory investigations. Our observations in rats demonstrate that cocaine depending on the dose and routes of administration induces profound hyperthermia, increased plasma and brain serotonin levels leading to BBB breakdown and brain edema formation. Furthermore, cocaine was able to enhance cellular stress as seen by upregulation of heat shock protein (HSP 72 kD) expression and resulted in marked neuronal and glial cell damages at the time of the BBB dysfunction. Taken together, these observations are the first to suggest that cocaine-induced BBB disruption is instrumental in precipitating brain pathology. The possible mechanisms of cocaine-induced BBB breakdown and neurotoxicity are discussed.
Corticotropin-releasing factor (CRF) is the primary factor involved in controlling the release of ACTH from the anterior pituitary and also acts as a neurotransmitter in a variety of brain systems. The actions of CRF are mediated by G-protein coupled membrane bound receptors and a high affinity CRF receptor, CRF1, has been previously cloned and functionally characterized. We have recently isolated a cDNA encoding a second member of the CRF receptor family, designated CRF2, which displays approximately 70% homology at the nucleotide level to the CRF1 receptor and exhibits a distinctive pharmacological profile. The present study utilized in situ hybridization histochemistry to localize the distribution of CRF2 receptor mRNA in rat brain and pituitary gland and compared this with the distribution of CRF1, receptor expression. While CRF1 receptor expression was very high in neocortical, cerebellar, and sensory relay structures, CRF2 receptor expression was generally confined to subcortical structures. The highest levels of CRF2 receptor mRNA in brain were evident within the lateral septal nucleus, the ventromedial hypothalamic nucleus and the choroid plexus. Moderate levels of CRF2 receptor expression were evident in the olfactory bulb, amygdaloid nuclei, the paraventricular and suraoptic nuclei of the hypothalamus, the inferior colliculus and 5-HT-associated raphe nuclei of the midbrain. CRF2-expressing cells were also evident in the bed nucleus of the stria terminalis, the hippocampal formation and anterior and lateral hypothalmic areas. In addition, CRF2 receptor mRNA was also found in cerebral arterioles throughout the brain. Within the pituitary gland, CRF2 receptor mRNA was detectable only at very low levels in scattered cells while CRF1 receptor mRNA was readily detectable in anterior and intermediate lobes. This heterogeneous distribution of CRF1 and CRF2 receptor mRNA suggests distinctive functional roles for each receptor in CRF-related systems. The CRF1 receptor may be regarded as the primary neuroendocrine pituitary CRF receptor and important in cortical, cerebellar and sensory roles of CRF. The anatomical distribution of CRF2 receptor mRNA indicates a role for this novel receptor in hypothalamic neuroendocrine, autonomic and general behavioral actions of central CRF.
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.
In the present experiments, we characterized the action of human/rat corticotropin-releasing factor (h/rCRF) and acute stress (1 hr of immobilization) on hippocampus-dependent learning and on synaptic plasticity in the mouse hippocampus. We first showed that h/rCRF application and acute stress facilitated (primed) long-term potentiation of population spikes (PS-LTP) in the mouse hippocampus and enhanced context-dependent fear conditioning. Both the priming of PS-LTP and the improvement of context-dependent fear conditioning were prevented by the CRF receptor antagonist [Glu(11,16)]astressin. PS-LTP priming and improved learning were also reduced by the protein kinase C inhibitor bisindolylmaleimide I. Acute stress induced the activation of Ca2+/calmodulin-dependent kinase II (CaMKII) 2 hr after the end of the stress session. The CaMKII inhibitor KN-62 antagonized the stress-mediated learning enhancement, however, with no effect on PS-LTP persistence. Thus, long-lasting increased neuronal excitability as reflected in PS-LTP priming appeared to be essential for the enhancement of learning in view of the observation that inhibition of PS-LTP priming was associated with impaired learning. Conversely, it was demonstrated that inhibition of CaMKII activity reduced contextual fear conditioning without affecting PS-LTP priming. This observation suggests that priming of PS-LTP and activation of CaMKII represent two essential mechanisms that may contribute independently to long-term memory.
Corticotropin-releasing factor (CRF) exerts a key neuroregulatory control on stress responses in various regions of the mammalian brain, including the hippocampus. Using hippocampal slices, extracts, and whole animals, we investigated the effects of human/rat CRF (h/rCRF) on hippocampal neuronal excitability and hippocampus-dependent learning in two mouse inbred strains, BALB/c and C57BL/6N. Intracellular recordings from slices revealed that application of h/rCRF increased the neuronal activity in both mouse inbred strains. Inhibition of protein kinase C (PKC) by bisindolylmaleimide I (BIS-I) prevented the h/rCRF effect only in hippocampal slices from BALB/c mice but not in slices from C57BL/6N mice. Inhibition of cAMP-dependent protein kinase (PKA) by H-89 abolished the h/rCRF effect in slices from C57BL/6N mice, with no effect in slices from BALB/c mice. Accordingly, h/rCRF elevated PKA activity in hippocampal slices from C57BL/6N mice but increased only PKC activity in the hippocampus of BALB/c mice. These differences in h/rCRF signal transduction were also observed in hippocampal membrane suspensions from both mouse strains. In BALB/c mice, hippocampal CRF receptors coupled to G(q/11) during stimulation by h/rCRF, whereas they coupled to G(s), G(q/11), and G(i) in C57BL/6N mice. As expected on the basis of the slice experiments, h/rCRF improved context-dependent fear conditioning of BALB/c mice in behavioral experiments, and BIS-I prevented this effect. However, although h/rCRF increased neuronal spiking in slices from C57BL/6N mice, it did not enhance conditioned fear. These results indicate that the CRF system activates different intracellular signaling pathways in mouse hippocampus and may have distinct effects on associative learning depending on the mouse strain investigated.
The role of the ventral subiculum in cocaine- or cue-induced cocaine-seeking behavior was investigated in rats tested on a between-session reinstatement model. Rats were trained to self-administer cocaine (0.25 mg/infusion, i.v.) in a lever-pressing operant task in a daily 2 hr session. Responding was reinforced contingent on a modified fixed-ratio 5 schedule. Reinstatement tests began after the lever-pressing behavior was extinguished in the absence of cocaine and conditioned cues (light and tone). Bilateral microinjections of lidocaine (100 microg) into the ventral subiculum decreased cocaine- or cue-induced reinstatement of cocaine-seeking behavior compared with saline microinjections into the same area in another group of rats. Lidocaine microinjections, however, had no effect on cocaine self-administration behavior or food-maintained or food-reinstated responding. Collectively, these results suggest that the ventral subiculum plays an important role in cocaine-seeking behavior. Considering the role of this structure in context learning, our data suggest that the full expression of cocaine- or cue-induced reinstatement may depend on the context in which the cocaine experience occurred.
Although the medial prefrontal cortex (mPFC) plays a critical role in cocaine addiction, the effects of chronic cocaine on mPFC neurons remain poorly understood. Here, we performed visualized current-clamp recordings to determine the effects of repeated cocaine administration on the membrane excitability of mPFC pyramidal neurons in rat brain slices. Following repeated cocaine administration (15 mg/kg/day i.p. for 5 days) with a 3-day withdrawal, alterations in membrane properties, including increased input resistance, reduced intensity of intracellular injected currents required for generation of Na(+)-dependent spikes (rheobase), and an increased number of spikes evoked by depolarizing current pulses were observed in mPFC neurons. The current-voltage relationship was also altered in cocaine-pretreated neurons showing reduced outward rectification during membrane depolarization and decreased inward rectification during membrane hyperpolarization. Application of the K(+) channel blocker Ba(2+) depolarized the resting membrane potential (RMP) and enhanced membrane potential response to injection of hyperpolarizing current pulses. However, the effects of Ba(2+) on RMP and hyperpolarized membrane potentials were significantly attenuated in cocaine-withdrawn neurons compared with saline-pretreated cells. These findings indicate that repeated cocaine administration increased the excitability of mPFC neurons after a short-term withdrawal, possibly via reducing the activity of the potassium inward rectifiers (K(ir)) and voltage-gated K(+) currents. Similar changes were also observed in cocaine-pretreated mPFC neurons after a long-term (2-3 weeks) withdrawal, revealing a persistent increase in excitability. These alterations in mPFC neuronal excitability may contribute to the development of behavioral sensitization and withdrawal effects following chronic cocaine exposure.
Corticotropin-releasing factor (CRF) and urocortin (Ucn I) are endogenous members among a family of CRF-related peptides that activate two different and synaptically localized G-protein-coupled receptors, CRF 1 and CRF 2 . These peptides and their receptors have been implicated in stress responses and stress with cocaine abuse.
In this study, we observed significant alterations in excitatory transmission and CRF-related peptide regulation of excitatory transmission in the lateral septum mediolateral nucleus (LSMLN) after chronic cocaine administration. In brain slice recordings from the LSMLN of control (saline-treated) rats, glutamatergic synaptic transmission was facilitated by activation of CRF 1 receptors with CRF but was depressed after activation of CRF 2 receptors with Ucn I. After acute withdrawal from a chronic cocaine administration regimen, CRF 1 activation remained facilitatory, but CRF 2 activation facilitated rather than depressed LSMLN EPSCs. These alterations in CRF 2 effects occurred through both presynaptic and postsynaptic mechanisms. In saline-treated rats, CRF 1 and CRF 2 coupled predominantly to protein kinase A signaling pathways, whereas after cocaine withdrawal, protein kinase C activity was more prominent and likely contributed to the CRF 2 -mediated presynaptic facilitation. Neither CRF nor Ucn I altered monosynaptic GABA A -mediated IPSCs before or after chronic cocaine administration, suggesting that loss of GABA A -mediated inhibition could not account for the facilitation. This switch in polarity of Ucn I-mediated neuromodulation, from a negative to positive regulation of excitatory glutamatergic transmission after chronic cocaine administration, could generate an imbalance in the brain reward circuitry associated with the LSMLN.
Drug-induced adaptations in the prefrontal cortex (PFC) contribute to several core aspects of addictive behaviors, but the underlying neuronal processes remain essentially unknown. Here, we demonstrate that repeated in vivo exposure to cocaine persistently reduces the voltage-gated K+ current (VGKC) in PFC pyramidal neurons, resulting in enhanced membrane excitability. Analysis of dopamine D1-class receptor (D1R)-mediated modulation of VGKC indicates that, despite the absence of direct D1R stimulation, downstream D1 signaling (the cAMP/protein kinase A pathway) is increased during withdrawal from chronic cocaine treatment and plays a central role in the drug-induced membrane plasticity in PFC. This long-lasting, cocaine-induced plasticity of membrane excitability in PFC pyramidal neurons may contribute to the impaired decision making and drug craving that characterize cocaine withdrawal.
The amygdala is part of the brain reward circuitry that plays a role in cocaine-seeking and abstinence in animals and cocaine craving and relapse in humans. Cocaine-seeking is elicited by cocaine-associated cues, and the basolateral amygdala (BLA) and CeA are essential in forming and communicating drug-related associations that are thought to be critical in long-lasting relapse risk associated with drug addiction. Here we simulated a cue stimulus with high-frequency stimulation (HFS) of the BLA-CeA pathway to examine mechanisms that may contribute to drug-related associations. We found enhanced long-term potentiation (LTP) after 14-day but not 1-day withdrawal from 7-day cocaine treatment mediated through N-methyl-d-aspartate (NMDA) receptors (NRs), L-type voltage-gated calcium channels (L-VGCCs), and corticotropin-releasing factor (CRF)(1) receptors; this was accompanied by increased phosphorylated NR1 and CRF(1) protein not associated with changes in NMDA/AMPA ratios in amygdalae from cocaine-treated animals. We suggest that these signaling mechanisms may provide therapeutic targets for the treatment of cocaine cravings.
Drug addicts make poor decisions. These decision-making deficits have been modeled in addicts and laboratory animals using reversal-learning tasks. However, persistent reversal-learning impairments have been shown in rats and monkeys only after noncontingent cocaine injections. Current thinking holds that to represent the human condition effectively, animal models of addiction must utilize self-administration procedures in which drug is earned contingently; thus, it remains unclear whether reversal-learning deficits caused by noncontingent cocaine exposure are relevant to addiction. To test whether reversal learning deficits are caused by contingent cocaine exposure, we trained rats to self-administer cocaine, assessed cue-induced cocaine seeking in extinction tests after 1 and 30 d of withdrawal, and then tested for reversal learning more than a month later. We found robust time-dependent increases in cue-induced cocaine seeking in the two extinction tests (incubation of craving) and severe reversal-learning impairments.
Basolateral amygdala (BLA) neurons provide a major excitatory input to medial prefrontal cortex (mPFC)-layer V pyramidal neurons. Under stressful conditions, commonly associated with chronic cocaine abuse, altered BLA-to-mPFC synaptic transmission could lead to defective emotional information processing and decision making within the mPFC and result in misguided and inappropriate behaviors. We examined the effects of cocaine administered chronically in vivo on EPSCs recorded from a putative BLA-mPFC pathway in vitro and their modulation by dopamine (DA), corticotropin-releasing factor (CRF), and their combination (DA plus CRF). In saline-treated animals, activation of D(1/5) receptors depressed BLA-mPFC EPSCs, whereas CRF1 receptor activation alone had no effect on EPSCs. Activating D(1/5) and CRF1 receptors in combination, however, worked synergistically through presynaptic and postsynaptic mechanisms to depress EPSCs to levels greater than D(1/5) receptor activation alone. After chronic cocaine administration, the function of DA(1/5) and CRF receptors switched from inhibitory to excitatory. In slices from cocaine-treated animals, putative BLA-mPFC EPSCs were depressed through a presynaptic mechanism. Now, activation of either D(1/5) or CRF2 receptors increased the cocaine-induced, depressed EPSCs. Additionally, simultaneous activation of presynaptic D(1/5) and CRF2 receptors led to further enhancement of EPSCs. These data indicate that CRF acting synergistically with DA normally potentiates D(1/5)-induced synaptic depression. However, after chronic cocaine, the combined synergistic actions of DA and CRF switched polarity to enhance facilitation of BLA-mPFC glutamatergic transmission. Also unmasked after acute withdrawal from chronic cocaine are endogenous, tonic-inhibitory D2-like and tonic-facilitatory CRF2 receptor actions. These multiple functional and receptor changes may underlie the altered, possibly aberrant, decision-making process after chronic cocaine.
Psychostimulant use increases anxious behavior, likely through interactions between central corticotropin-releasing factor (CRF) and serotonergic systems. The current study examined whether chronic amphetamine treatment (2.5mg/kg, 14 days) or withdrawal altered CRF receptor densities in the serotonergic dorsal raphe nucleus (dRN). Amphetamine treatment increased CRF(2) receptor densities in most subregions of the dRN, and CRF(2) receptors were still elevated following 6 weeks of withdrawal. No changes in CRF(1) receptor densities were observed following amphetamine treatment or during withdrawal. Selective increases in dRN CRF(2) receptors may be related to increased anxiety-like behaviors following psychostimulant use.
Previously, we have shown that long-term potentiation (LTP) in hippocampus of Lewis rats was significantly modulated by cocaine self-administration. Using a single train of high-frequency stimulation of 100 Hz for 1s (HFS), we found an enhancement of LTP after cocaine self-administration that was maintained even during the extinction of this behavior. However, the effects of cocaine self-administration on a hippocampal-dependent spatial learning task were unknown. Therefore, in the present study our first objective was to analyze if cocaine self-administration might affect the performance in a hippocampus-dependent task, such as the Morris water maze test. Male adult Lewis (LEW) rats self-administered cocaine (1 mg/kg/injection) or saline (0.9% NaCl) for 3 weeks. Three hours after finishing the last self-administration session, animals were submitted to Morris water maze training for 3 consecutives days. A memory test was carried out 24 h after the last training session. No significant differences were found in escape latencies and time spent in the quadrant where the platform was located during training. Given that we did not find any cocaine effect on this spatial learning task, our second objective was to estimate indirectly if brain cocaine levels have failed to modulate LTP in animals that were performing the water maze trials. To this end, we tested if cocaine application to hippocampal slices of naïve subjects was able to evoke LTP. The results indicated that cocaine produced an enhanced LTP in these hippocampal slices. Taking together, the results of the present study suggest that hippocampal LTP-like processes generated after cocaine self-administration are not related to spatial learning hippocampal-dependent tasks, such as the water maze test.
Corticotropin-releasing factor (CRF) is the primary factor involved in controlling the release of ACTH from the anterior pituitary and also acts as a neurotransmitter in a variety of brain systems. The actions of CRF are mediated by G-protein coupled membrane bound receptors and a high affinity CRF receptor, CRF1, has been previously cloned and functionally characterized. We have recently isolated a cDNA encoding a second member of the CRF receptor family, designated CRF2, which displays approximately 70% homology at the nucleotide level to the CRF1 receptor and exhibits a distinctive pharmacological profile. The present study utilized in situ hybridization histochemistry to localize the distribution of CRF2 receptor mRNA in rat brain and pituitary gland and compared this with the distribution of CRF1, receptor expression. While CRF1 receptor expression was very high in neocortical, cerebellar, and sensory relay structures, CRF2 receptor expression was generally confined to subcortical structures. The highest levels of CRF2 receptor mRNA in brain were evident within the lateral septal nucleus, the ventromedial hypothalamic nucleus and the choroid plexus. Moderate levels of CRF2 receptor expression were evident in the olfactory bulb, amygdaloid nuclei, the paraventricular and suraoptic nuclei of the hypothalamus, the inferior colliculus and 5-HT-associated raphe nuclei of the midbrain. CRF2-expressing cells were also evident in the bed nucleus of the stria terminalis, the hippocampal formation and anterior and lateral hypothalmic areas. In addition, CRF2 receptor mRNA was also found in cerebral arterioles throughout the brain. Within the pituitary gland, CRF2 receptor mRNA was detectable only at very low levels in scattered cells while CRF1 receptor mRNA was readily detectable in anterior and intermediate lobes. This heterogeneous distribution of CRF1 and CRF2 receptor mRNA suggests distinctive functional roles for each receptor in CRF-related systems. The CRF1 receptor may be regarded as the primary neuroendocrine pituitary CRF receptor and important in cortical, cerebellar and sensory roles of CRF. The anatomical distribution of CRF2 receptor mRNA indicates a role for this novel receptor in hypothalamic neuroendocrine, autonomic and general behavioral actions of central CRF.
The regional distribution of corticotropin-releasing factor1 (CRF1) and CRF2 binding sites was assessed autoradiographically in adult rat brain. The differential pharmacological profiles of the CRF1 and CRF2 receptor subtypes were used for the discrimination of the CRF1 and CRF2 receptor subtypes in rat brain. Pharmacological characterization at the human CRF1 receptor subtype, expressed in baculovirus-infected Sf9 cells, showed high affinity binding (Ki < or = 10.0 nM) for the peptide agonists sauvagine, urotensin I, rat/human CRF, and ovine CRF. Pharmacological characterization at the rat CRF2 receptor subtype expressed in CHO cells showed a rank order affinity for the peptide agonists such that sauvagine, urotensin I and rat/human CRF showed high affinity binding whereas ovine CRF had a Ki value of 300 nM. Based on this differential binding affinity for ovine CRF, [125I]sauvagine binding in the presence of increasing concentrations of ovine CRF was used to discriminate CRF1 from CRF2 receptor subtypes in rat brain. The CRF1 receptor subtype was found to be localized to various regions of the cerebellum, as well as to several cortical areas. The CRF2 receptor subtype was shown to be localized to the lateral septal nucleus, entorhinal cortex, and to amygdaloid and hypothalamic regions. The present autoradiographic findings provide evidence that each subtype has a distinct regional distribution, thus strengthening the suggestion that CRF1 and CRF2 receptors serve different roles in mediating CRF function. Such data suggest that the development of CRF receptor subtype selective antagonists should help to delineate the role of CRF1 and CRF2 receptor subtypes in central nervous system function.
This is publication number 11130-NP from The Scripps Research Institute. Research was supported by National Institutes of Health grants DA04043, DA04398, and DA08467 from the National Institute on Drug Abuse and AA06420 and AA08459 from the National Institute on Alcohol Abuse and Alcoholism. The authors would like to thank Mike Arends for his valuable assistance with manuscript preparation.
We have previously demonstrated that intra-hippocampal injection of corticotrophin-releasing factor improved memory retention of an inhibitory avoidance learning in rats; while the electrophysiological effects corticotrophin-releasing factor produces on hippocampal neurons are largely uncharacterized. In the present study, we found that corticotrophin-releasing factor injected into the dentate gyrus of hippocampus produced a dose-dependent and long-lasting enhancement in synaptic efficacy of these neurons, as measured by an increase in the amplitude and slope of population excitatory postsynaptic potentials, as well as the amplitude of population spike. The onset of corticotrophin-releasing factor-induced potentiation was slow. It was observed approximately 40-60 min after corticotrophin-releasing factor administration and lasted for more than 5 h. This effect of corticotrophin-releasing factor was blocked by pretreatment with the cyclase-adenosine-3,5-monophosphate (cAMP) inhibitor Rp-adenosine-3,5-cyclic monophosphothiolate triethylamine (Rp-cAMPS) and partially blocked by the N-methyl-D-aspartate receptor antagonist MK-801. Further, pretreatment with corticotrophin-releasing factor receptor antagonist dose-dependently diminished tetanization-induced long-term potentiation, and corticotrophin-releasing factor and tetanic stimuli had an additive effect on hippocampal neuron excitation. Moreover, direct injection of corticotrophin-releasing factor increased cAMP level in the dentate gyrus. These results together suggest that corticotrophin-releasing factor-induced potentiation simulates the late phase of tetanization-induced long-term potentiation and cAMP seems to be the messenger mediating this effect. Moreover, corticotrophin-releasing factor-induced potentiation and long-term potentiation may share some similar mechanisms, and corticotrophin-releasing factor is probably involved in the neural circuits underlying long-term potentiation. Thus, corticotrophin-releasing factor may play an important role in modulating synaptic plasticity in the hippocampus.
Treatment efforts for cocaine addiction are hampered by high relapse rates. To map brain areas underlying relapse, we used electrical brain stimulation and intracranial injection of pharmacological compounds after extinction of cocaine self-administration behavior in rats. Electrical stimulation of the hippocampus containing glutamatergic fibers, but not the medial forebrain bundle containing dopaminergic fibers, elicited cocaine-seeking behavior dependent on glutamate in the ventral tegmental area. This suggests a role for glutamatergic neurotransmission in relapse to cocaine abuse. The medial forebrain bundle electrodes supported intense electrical self-stimulation. These findings suggest a dissociation of neural systems subserving positive reinforcement (self-stimulation) and incentive motivation (relapse).
Long-lasting neuroadaptations that occur during drug use and remain after withdrawal are thought to contribute to the persisting and compulsive nature of drug addiction and relapse. At the molecular and cellular levels, mechanisms that have been implicated in the normal process of memory formation are increasingly being identified as potential contributors to the persistence of the addicted state. To investigate the effect of cocaine self-administration on synaptic plasticity, rats were allowed to self-administer 0.5 mg/kg/infusion cocaine or 0.9% NaCl during 90 min sessions for 15 consecutive days. These cocaine and saline self-administration subjects were then restricted to their home cages for 3, 30, or 100 days (3, 30, and 100 day cocaine/saline withdrawal groups) before the assessment of the induction and reversal of long-term potentiation (LTP) in the CA1 region of hippocampal slices. The magnitude of LTP was increased in the 3-day cocaine withdrawal group as compared with the 3-day saline withdrawal group, but this effect was short lived, as the 30-day cocaine and saline withdrawal groups exhibited similar LTP magnitudes. Interestingly, LTP was significantly decreased in the 100-day cocaine withdrawal group compared with the 100-day saline withdrawal group. These results support the hypothesis that the capacity for LTP is persistently altered after withdrawal from exposure to an addictive substance. In addition, this alteration can be differentially expressed such that depending upon the duration of the withdrawal period following the last drug exposure, LTP may be enhanced, unchanged, or suppressed.
In order to further characterize the actions of cocaine on synaptic activity in the hippocampus, recordings of field excitatory postsynaptic potentials in the CA1 region of the rat hippocampal slice preparation were used to monitor drug effects on long-term potentiation (LTP) evoked in response to stimulation of the Schaffer collateral pathway. Cocaine had dose-dependent, biphasic effects on the magnitude of LTP at these excitatory synapses in the stratum radiatum ranging from a significant enhancement of LTP at intermediate drug concentrations (5-10 microM), to an inhibition of LTP at a relatively high drug concentration (30 microM). The local anesthetic lidocaine had only inhibitory effects on the induction of LTP at all concentrations examined (10-75 microM), whereas the monoamine transporter antagonists, WIN 35348 (1 microM) or GBR 12935 (5 microM) significantly enhanced the magnitude of LTP. The D(2)-like dopamine receptor antagonist, eticlopride was effective in preventing this action of cocaine, whereas pretreatment with the D(1/5) antagonist, SCH 23390 was ineffective. These results suggest that endogenously released dopamine, in the presence of cocaine (5-10 microM), can act via D(2)-like receptors to significantly increase the magnitude of LTP in the CA1 region of the hippocampus.
We examined the influence of CP 154,526, a selective antagonist of corticotropin-releasing factor (CRF)1 receptors, in the locomotor, sensitizing, discriminative stimulus and rewarding effects of cocaine, as well as on the cocaine-induced reinstatement of cocaine-seeking behavior in male Wistar rats. CP 154,526 in doses of 5, 10 and 20 mg/kg, which did not affect basal locomotor activity, dose-dependently reduced the hyperactivation evoked by cocaine. To assess the effects of CP 154,526 on the expression of cocaine sensitization, the rats were injected with either saline or cocaine (10 mg/kg) for 5 days, and were then challenged with cocaine (10 mg/kg) after pretreatment with saline or CP 154,526 on day 5 of withdrawal. The cocaine-induced hyperactivity in sensitized rats was reduced by CP 154,526 (10 and 20 mg/kg). In rats trained to discriminate cocaine (10 mg/kg) from saline, pretreatment with CP 154,526 (5-20 mg/kg) did not affect the cocaine (1.25-10 mg/kg)-induced discriminative stimulus effects. In a self-administration model, the rats were trained to self-administer cocaine (0.5 mg/kg/infusion) in the FR 5 schedule of reinforcement. Administration of CP 154,526 (10-20 mg/kg) did not alter the rewarding effects of cocaine, assessed as the number of active-lever presses and infusions; however, following a 10-day extinction phase, CP 154,526 (5-20 mg/kg) significantly decreased in a dose-dependent manner the cocaine (10 mg/kg) priming-induced reinstatement of cocaine-seeking behavior. The present study implies that CRF1 receptors control the expression of cocaine hyperactivation and sensitization as well as the cocaine-induced relapse behavior, but do not play any role in cocaine discrimination and self-administration. These findings may suggest that CRF1 receptor antagonists should be considered as possible medications in the treatment of cocaine addiction.
Dysfunctioning of corticotropin-releasing factor (CRF) and its receptors (CRF(1) and CRF(2)) has been linked to the development of stress-related disorders, such as affective disorders and drug abuse. The molecular characterization of CRF(1) and CRF(2) receptors and their splice variants has generated detailed information on their pharmacology, tissue distribution and physiology. In addition, the recent development of a small molecule CRF(1) antagonist has provided important information on the contribution of this receptor to the development of stress-related diseases. Despite the high homology to the CRF(1) receptor and the generation of peptide-based research tools, the physiological role of the CRF(2) receptor is largely unclear. This is due to different expression patterns in rodents and primates and the lack of brain-penetrant CRF(2)-selective small molecule antagonists. However, the CRF(2) receptor may be important for motivational types of behavior essential for survival, such as feeding and defense and impacts on cardiovascular function.
Drug addiction may involve learning and memory processes requiring the participation of hippocampal formation. One of the best studied examples of hippocampal synaptic plasticity is the long-term potentiation (LTP) which usually occurs when hippocampal synapses are stimulated with high-frequency stimulation. The aim of this work has been to study the effect of extinction of cocaine self-administration behavior on synaptic plasticity in rat hippocampal slices. LTP was induced using a tetanization paradigm consisting of a single train of high-frequency (100 Hz) stimulation for one second. This tetanization protocol evoked a greater and more perdurable LTP in slices obtained after 10 days of extinction of cocaine self-administration (1 mg/kg/injection) than that elicited in slices from saline self-administering (0.9% NaCl) animals. In addition, this LTP facilitation in animals which have followed the cocaine self-administration extinction protocol was very similar to that obtained in slices from cocaine self-administering animals. These results suggest that chronic cocaine self-administration induces enduring neuroadaptive changes in hippocampal synaptic plasticity which last even after the extinction of this behavior and that they may be involved in cocaine dependence.
Recent data indicate that alcohol dependence induces long-term neuroadaptations that recruit a negative emotional state. This leads to excessive alcohol ingestion motivated by relief of negative emotionality. A key mechanism in this transition to negative reinforcement is a recruitment of corticotropin-releasing factor (CRF) signaling within the amygdala. Long term upregulation of CRF(1) receptors is observed in the amygdala following a history of dependence, and CRF antagonists selectively block emotionality, excessive alcohol drinking and stress-induced reinstatement of alcohol-seeking in post-dependent animals. Innate upregulation of CRF(1) receptor expression mimics the post-dependent phenotype, both with regard to emotional responses and ethanol self-administration. Therefore, the CRF system is emerging as a key element of the neuroadaptive changes driving alcoholism and as a major target for its treatment.
Stress is an important factor known to increase alcohol and drug relapse risk. This paper examines the stress-related processes that influence addiction relapse. First, individual patient vignettes of stress- and cue-related situations that increase drug seeking and relapse susceptibility are presented. Next, empirical findings from human laboratory and brain-imaging studies that are consistent with clinical observations and support the specific role of stress processes in the drug-craving state are reviewed. Recent findings on differences in stress responsivity in addicted versus matched community social drinkers are reviewed to demonstrate alterations in stress pathways that could explain the significant contribution of stress-related mechanisms on craving and relapse susceptibility. Finally, significant implications of these findings for clinical practice are discussed, with a specific focus on the development of novel interventions that target stress processes and drug craving to improve addiction relapse outcomes.
Corticotropin-releasing factor (CRF), which activates the hypothalamic-pituitary- adrenal axis under stress, also has proinflammatory peripheral effects possibly through mast cells. The purpose of this study was to investigate the effect of urocortin (UCN), a 40-amino-acid CRF family peptide, on degranulation and intracellular calcium of rat lung mast cells. The activation and degranulation of mast cells were observed by Toluidine blue staining and transmission electron microscope. The intracellular calcium was investigated using confocal laser scanning microscopy and flow cytometry. The results indicated that all the three different concentrations of UCN (0.1, 1 and 10 microM) significantly induced the activation and degranulation of rat lung mast cells in vitro. This effect was markedly blocked by selective CRF receptor 1 (CRF-R1) antagonist antalarmin, but not by specific CRF receptor 2 (CRF-R2) antagonist antisauvagine-30 (anti-Svg-30). The results also showed that UCN caused a rapid peak increase in [Ca(2+)](i) at point of 300s after UCN treatment, followed by a decrease to a sustained plateau phase. The peak increase in [Ca(2+)](i) induced by UCN was significantly inhibited by antalarmin, but not by anti-Svg-30. This effect of UCN on [Ca(2+)](i) in rat lung mast cells was also found by flow cytometry. Regression analysis revealed a positive correlation between mast cells degranulation extent and the maximum value of [Ca(2+)](i) (P < 0.01). Taken together, our present study suggested that UCN induced the increase of [Ca(2+)](i) and degranulation of rat lung mast cells through CRF-R1. These findings may have implications for the pathophysiology of allergic and inflammatory lung disorders such as asthma, which is closely associated with mast cell activation and degranulation.
Substantial evidence indicates that brain neurons containing and secreting noradrenaline and corticotropin-releasing factor (CRF) are activated during stress, and that physiological and behavioural responses observed during stress can be induced by exogenous administration of CRF and adrenoceptor agonists. This review focusses on the evidence for the involvement of these two factors in stress-related responses, and the inter-relationships between them. The possible abnormalities of these two systems in depressive illness are also discussed.
A key role of corticotrophin-releasing factor in alcohol dependence
- Heilig