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Generation of OxtrCre:GFP mice Diagram showing: top, insertion of ires-mnCre:GFP construct just 3’ of the termination codon of the Oxtr gene; bottom, the targeting vector. Some key restriction enzymes sites used for cloning are shown. See Methods for details
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Brain regions that regulate fluid satiation are not well characterized, yet are essential for understanding fluid homeostasis. We found that oxytocin-receptor-expressing neurons in the parabrachial nucleus of mice (OxtrPBN neurons) are key regulators of fluid satiation. Chemogenetic activation of OxtrPBN neurons robustly suppressed noncaloric fluid...
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... Under both water and Na depletion (bottom), Ang II activates both types of neurons in the absence of Na x or CCK signals. Modified from Matsuda et al. (2017 (Ryan et al., 2017). Both HSD2 neurons and LPBN oxytocin receptor-expressing neurons have neural connections with the vBNST, the target of saltappetite neurons in the SFO, suggesting the conversion of salt-appetite signals in the vBNST and the existence of some regulatory neural mechanisms in this nucleus. ...
The brain possesses intricate mechanisms for monitoring sodium (Na) levels in body fluids. During prolonged dehydration, the brain detects variations in body fluids and produces sensations of thirst and aversions to salty tastes. At the core of these processes Na x , the brain's Na sensor, exists. Specialized neural nuclei, namely the subfornical organ (SFO) and organum vasculosum of the lamina terminalis (OVLT), which lack the blood–brain barrier, play pivotal roles. Within the glia enveloping the neurons in these regions, Na x collaborates with Na ⁺ /K ⁺ ‐ATPase and glycolytic enzymes to drive glycolysis in response to elevated Na levels. Lactate released from these glia cells activates nearby inhibitory neurons. The SFO hosts distinct types of angiotensin II‐sensitive neurons encoding thirst and salt appetite, respectively. During dehydration, Na x ‐activated inhibitory neurons suppress salt‐appetite neuron's activity, whereas salt deficiency reduces thirst neuron's activity through cholecystokinin. Prolonged dehydration increases the Na sensitivity of Na x via increased endothelin expression in the SFO. So far, patients with essential hypernatremia have been reported to lose thirst and antidiuretic hormone release due to Na x ‐targeting autoantibodies. Inflammation in the SFO underlies the symptoms. Furthermore, Na x activation in the OVLT, driven by Na retention, stimulates the sympathetic nervous system via acid‐sensing ion channels, contributing to a blood pressure elevation.
... The decay time in gCaMP6f was 142ms, whereas gCaMP6m and gCaMP6s were 270ms and 550ms, respectively (Kim et al., 2014, Chen et al., 2013. Moreover, all brainstem studies to date using head-mounted miniscope studies have used the slower variants of GCaMP6 such as gCaMP6m (Ryan et al., 2017) or gCaMP6s (Jarvie et al., 2021, Schwenkgrub et al., 2020 due to their brighter fluorescence compared to the typically used fast variant (Ai95D). ...
... Satiation is a vital signal preventing overconsumption of food and fluid and is essential for maintaining energy and fluid homeostasis (Morton et al., 2014;Ryan, 2018). A key brain region regulating satiation is the lateral parabrachial nucleus (LPBN) in the hindbrain (Palmiter, 2018), which comprises several subdivisions, including the dorsolateral (dl) LPBN which controls fluid satiation, and the external lateral (el) LPBN which primarily controls food satiation (Carter et al., 2013;Ryan et al., 2017). The major phenotype of LPBN neurons is excitatory, glutamatergic neurons (Pauli et al., 2022); however, there are several markers which have been identified for neurons within the LPBN subdivisions, including Oxtr (oxytocin receptor) predominantly for dl LPBN neurons and CGRP (calcitonin gene-related peptide) for el LPBN neurons. ...
... Chemogenetically activating Oxtr PBN neurons suppresses fluid intake, whereas activating CGRP PBN neurons primarily suppresses food intake (Campos et al., 2016(Campos et al., , 2018Carter et al., 2013;Ryan et al., 2017). ...
... Activating Oxtr PBN neurons decreased intake of water, but not highly caloric, palatable fluids like 1 kcal/mL Ensure® (Ryan et al., 2017), suggesting LPBN neurons might differentiate solutions based on their caloric content and/or palatability; however, the underlying mechanism for this differentiation is unknown. This a vital research area, given that highly caloric, palatable drinks such as sodas (soft drinks) and alcoholic beverages are key contributors to the obesity epidemic (Schulze et al., 2004;Shelton & Knott, 2014) and are often advertised for their thirst-quenching properties. ...
Chemogenetic activation of oxytocin receptor‐expressing neurons in the parabrachial nucleus (OxtrPBN neurons) acts as a satiation signal for water. In this research, we investigated the effect of activating OxtrPBN neurons on satiation for different types of fluids. Chemogenetic activation of OxtrPBN neurons in male and female transgenic OxtrCre mice robustly suppressed the rapid, initial (15‐min) intake of several solutions after dehydration: water, sucrose, ethanol and saccharin, but only slightly decreased intake of Ensure®, a highly caloric solution (1 kcal/mL; containing 3.72 g protein, 3.27 g fat, 13.42 g carbohydrates, and 1.01 g dietary fibre per 100 mL). OxtrPBN neuron activation also suppressed cumulative, longer‐term (2‐h) intake of lower caloric, less palatable solutions, but not highly caloric, palatable solutions. These results suggest that OxtrPBN neurons predominantly control initial fluid‐satiation responses after rehydration, but not longer‐term intake of highly caloric, palatable solutions. The suppression of fluid intake was not because of anxiogenesis, but because OxtrPBN neuron activation decreased anxiety‐like behaviour. To investigate the role of different PBN subdivisions on the intake of different solutions, we examined FOS as a proxy marker of PBN neuron activation. Different PBN subdivisions were activated by different solutions: the dorsolateral PBN similarly by all fluids; the external lateral PBN by caloric but not non‐caloric solutions; and the central lateral PBN primarily by highly palatable solutions, suggesting PBN subdivisions regulate different aspects of fluid intake. To explore the possible mechanisms underlying the minimal suppression of Ensure® after OxtrPBN neuron activation, we demonstrated in in vitro slice recordings that the feeding‐associated agouti‐related peptide (AgRP) inhibited OxtrPBN neuron firing in a concentration‐related manner, suggesting possible inhibition by feeding‐related neurocircuitry of fluid satiation neurocircuitry. Overall, this research suggests that although palatable beverages like sucrose‐ and ethanol‐containing beverages activate fluid satiation signals encoded by OxtrPBN neurons, these neurons can be inhibited by hunger‐related signals (agouti‐related peptide, AgRP), which may explain why these fluids are often consumed in excess of what is required for fluid satiation.
... 83 Similarly, expression of ChR2 in a mixed population of Oxt + and oxytocin receptor + neurons of the PVN could elicit light-evoked action potentials and EPSCs in a subpopulation of oxytocin receptor + neurons of the parabrachial nucleus. 84 Others have found that the Oxt + PVN is glutamatergic, based on VGLUT2 immunolabeling in Oxt + PVN fibers and glutamate-dependent modulation of disynaptic IPSCs following light-evoked excitation of these fibers. 51,85,86 Finally, the Avp + PVN has recently been found to colocalize with VGlut2 based on FISH. ...
Many neuronal populations that release fast-acting excitatory and inhibitory neurotransmitters in the brain also contain slower-acting neuropeptides. These facultative peptidergic cell types are common, but it remains uncertain whether neurons that solely release peptides exist. Our fluorescence in situ hybridization, genetically targeted electron microscopy, and electrophysiological characterization suggest that most neurons of the non-cholinergic, centrally projecting Edinger-Westphal nucleus in mice are obligately peptidergic. We further show, using anterograde projection mapping, monosynaptic retrograde tracing, angled-tip fiber photometry, and chemogenetic modulation and genetically targeted ablation in conjunction with canonical assays for anxiety, that this peptidergic population activates in response to loss of motor control and promotes anxiety responses. Together, these findings elucidate an integrative, ethologically relevant role for the Edinger-Westphal nucleus and functionally align the nucleus with the periaqueductal gray, where it resides. This work advances our understanding of peptidergic modulation of anxiety and provides a framework for future investigations of peptidergic systems.
... Whether LPB neurons simply relay these afferent signals or actively process them remains an interesting question. Considering that the LPB receives diverse inputs from brain regions with functions related to internal state sensing and fear, including the nucleus of the solitary tract (NTS) 25,54 , the rostral ventrolateral medulla 55 , and the paraventricular hypothalamus 56 , we propose that the LPB may also incorporate other types of signals to modify thermal afferent signals. In support of this hypothesis, it has recently been suggested that the LPBel receives input from the NTS and sends projections to the posterior subthalamic nucleus to mediate innate fear-associated hypothermia 54 . ...
Thermal homeostasis is vital for mammals and is controlled by brain neurocircuits. Yet, the neural pathways responsible for cold defense regulation are still unclear. Here, we found that a pathway from the lateral parabrachial nucleus (LPB) to the dorsomedial hypothalamus (DMH), which runs parallel to the canonical LPB to preoptic area (POA) pathway, is also crucial for cold defense. Together, these pathways make an equivalent and cumulative contribution, forming a parallel circuit. Specifically, activation of the LPB → DMH pathway induced strong cold-defense responses, including increases in thermogenesis of brown adipose tissue (BAT), muscle shivering, heart rate, and locomotion. Further, we identified somatostatin neurons in the LPB that target DMH to promote BAT thermogenesis. Therefore, we reveal a parallel circuit governing cold defense in mice, which enables resilience to hypothermia and provides a scalable and robust network in heat production, reshaping our understanding of neural circuit regulation of homeostatic behaviors.
... Whether LPB neurons simply relay these afferent signals or actively process them remains an interesting question. Considering that the LPB receives diverse inputs from brain regions with functions related to internal state sensing and fear, including the nucleus of the solitary tract (NTS) 25,54 , the rostral ventrolateral medulla 55 , and the paraventricular hypothalamus 56 , we propose that the LPB may also incorporate other types of signals to modify thermal afferent signals. In support of this hypothesis, it has recently been suggested that the LPBel receives input from the NTS and sends projections to the posterior subthalamic nucleus to mediate innate fear-associated hypothermia 54 . ...
Thermal homeostasis is vital for mammals and is controlled by brain neurocircuits. Remarkable advances have been made in understanding how neurocircuits centered in the hypothalamic preoptic area (POA), the brain's thermoregulation center, control warm defense, whereas mechanisms by which the POA regulates cold defense remain unclear. Here, we confirmed that the pathway from the lateral parabrachial nucleus (LPB) to the POA, is critical for cold defense. Parallel to this pathway, we uncovered that a pathway from the LPB to the dorsomedial hypothalamus (DMH), namely the LPB-DMH pathway, is also essential for cold defense. Projection-specific blockings revealed that both pathways provide an equivalent and cumulative contribution to cold defense, forming a parallel circuit. Specifically, activation of the LPB-DMH pathway induced strong cold-defense responses, including increases in thermogenesis of brown adipose tissue (BAT), muscle shivering, heart rate, and physical activity. Further, we identified a subpopulation of somatostatin+ neurons in the LPB that target the DMH to promote BAT thermogenesis. Therefore, we reveal a parabrachial-hypothalamic parallel circuit in governing cold defense in mice. This not only enables resilience to hypothermia but also provides a scalable and robust network in heat production, reshaping our understanding of how neural circuits regulate essential homeostatic behaviors.
... Oxytocin has a tonic inhibitory action on water and saline solutions intakes (satiety signal), counterbalancing the actions of AngII and thus facilitating those of ANP (also in the kidney). Oxytocin receptors are found on neurons of the LPBN, which represent an important station for the circuits that regulates fluid ingestion and satiety, in particular by moderating water and salt intake to prevent or attenuate hypervolemia and hypernatremia (Ryan et al. 2017). However, in the case of extracellular thirst induced by hypotension, oxytocin has opposite effects, increasing water intake and antidiuretic responses (Bernal et al. 2015). ...
Animals can sense their changing internal needs and then generate specific physiological and behavioural responses in order to restore homeostasis. Water-saline homeostasis derives from balances of water and sodium intake and output (drinking and diuresis, salt appetite and natriuresis), maintaining an appropriate composition and volume of extracellular fluid. Thirst is the sensation which drives to seek and consume water, regulated in the central nervous system by both neural and chemical signals. Water and electrolyte homeostasis depends on finely tuned physiological mechanisms, mainly susceptible to plasma Na⁺ concentration and osmotic pressure, but also to blood volume and arterial pressure. Increases of osmotic pressure as slight as 1–2% are enough to induce thirst (“homeostatic” or cellular), by activation of specialized osmoreceptors in the circumventricular organs, outside the blood-brain barrier. Presystemic anticipatory signals (by oropharyngeal or gastrointestinal receptors) inhibit thirst when fluids are ingested, or stimulate thirst associated with food intake. Hypovolemia, arterial hypotension, Angiotensin II stimulate thirst (“hypovolemic thirst”, “extracellular dehydration”). Hypervolemia, hypertension, Atrial Natriuretic Peptide inhibit thirst. Circadian rhythms of thirst are also detectable, driven by suprachiasmatic nucleus in the hypothalamus. Such homeostasis and other fundamental physiological functions (cardiocircolatory, thermoregulation, food intake) are highly interdependent.
... This point is of crucial importance given that activation of G q and G i/o proteins have opposite functions on neuronal excitability, with the former favoring neuronal spiking and the latter preventing it. To our knowledge, all published studies investigating the effect of OT on neuronal firing found an activity increase, suggesting no G i/o coupling in neurons (Alberi et al., 1997;Barrett et al., 2021;Crane et al., 2020;Eliava et al., 2016;Hu et al., 2020a;Knobloch et al., 2012;Ryan et al., 2017;Hatton, 2004, 2007). However, since the recruitment of both pathways in astrocytes was shown, independently of OTR, to trigger calcium transients (Durkee et al., 2019;Mehina et al., 2017), differentiating the pathway recruited cannot be done based on their calcium activity. ...
The neuropeptide oxytocin has been in the focus of scientists for decades due to its profound and pleiotropic effects on physiology, activity of neuronal circuits and behaviors. Until recently, it was believed that oxytocinergic action exclusively occurs through direct activation of neuronal oxytocin receptors. However, several studies demonstrated the existence and functional relevance of astroglial oxytocin receptors in various brain regions in the mouse and rat brain. Astrocytic signaling and activity are critical for many important physiological processes including metabolism, neurotransmitter clearance from the synaptic cleft and integrated brain functions. While it can be speculated that oxytocinergic action on astrocytes predominantly facilitates neuromodulation via the release of gliotransmitters, the precise role of astrocytic oxytocin receptors remains elusive. In this review, we discuss the latest studies on the interaction between the oxytocinergic system and astrocytes, and give details of underlying intracellular cascades.
... Oxytocin then plays an important role in restoring sodium homeostasis, in part, by acting at the kidney to promote natriuresis [128]. Of particular relevance here, many studies have also suggested a role for oxytocin in the satiation of sodium appetite and reduction in sodium intake [129][130][131][132][133]. In addition to secreting oxytocin into the bloodstream, PVN oxytocinergic neurons are also capable of releasing oxytocin centrally via projections within the brain-some of these central projections are important for oxytocin's modulatory role in sodium appetite. ...
... A population of Oxtr-expressing neurons within the PBN that receive oxytocinergic projections from the PVN has recently been implicated in sodium appetite. Inhibition of these neurons through DREADDs increased salt intake in dehydrated, hyperosmotic, and ad libitum water access conditions, while activation did not alter salt intake following sodium depletion [133]. This suggests different populations of Oxtr-expressing neurons throughout the brain may play distinct roles in salt appetite and fluid homeostasis. ...
Sodium (Na+) is crucial for numerous homeostatic processes in the body and, consequentially, its levels are tightly regulated by multiple organ systems. Sodium is acquired from the diet, commonly in the form of NaCl (table salt), and substances that contain sodium taste salty and are innately palatable at concentrations that are advantageous to physiological homeostasis. The importance of sodium homeostasis is reflected by sodium appetite, an “all-hands-on-deck” response involving the brain, multiple peripheral organ systems, and endocrine factors, to increase sodium intake and replenish sodium levels in times of depletion. Visceral sensory information and endocrine signals are integrated by the brain to regulate sodium intake. Dysregulation of the systems involved can lead to sodium overconsumption, which numerous studies have considered causal for the development of diseases, such as hypertension. The purpose here is to consider the inverse—how disease impacts sodium intake, with a focus on stress-related and cardiometabolic diseases. Our proposition is that such diseases contribute to an increase in sodium intake, potentially eliciting a vicious cycle toward disease exacerbation. First, we describe the mechanism(s) that regulate each of these processes independently. Then, we highlight the points of overlap and integration of these processes. We propose that the analogous neural circuitry involved in regulating sodium intake and blood pressure, at least in part, underlies the reciprocal relationship between neural control of these functions. Finally, we conclude with a discussion on how stress-related and cardiometabolic diseases influence these circuitries to alter the consumption of sodium.
... Signals from receptor cells of the tongue that are activated by NaCl intake and project to the rNST were also found to converge in the lNPB, inhibiting its intake [46,87,88]. In addition, lPBN activity and Na intake suppression appear to be enhanced by oxytocinergic afferents from the parvocellular division of the hypothalamic paraventricular nucleus (pPVN) [89]. Inhibition of the lPBN has been related to the intake of highly concentrated (usually aversive) NaCl solutions, associated with endogenous opioid signaling and the central amygdala (see [8]). ...
... Accordingly, aldosterone and Ang II protect the organism against hypovolemic and hyponatremic states, whereas other chemical substances protect the organism against hypervolemia and hypernatremia. This is the case of OXY, which acts on the lPBN to inhibit Na intake [89] and acts on the kidney to stimulate Na excretion [243]. ...
Body sodium (Na) levels must be maintained within a narrow range for the correct functioning of the organism (Na homeostasis). Na disorders include not only elevated levels of this so-lute (hypernatremia), as in diabetes insipidus, but also reduced levels (hyponatremia), as in cerebral salt wasting syndrome. The balance in body Na levels therefore requires a delicate equilibrium to be maintained between the ingestion and excretion of Na. Salt (NaCl) intake is processed by receptors in the tongue and digestive system, which transmit the information to the nucleus of the solitary tract via a neural pathway (chorda tympani/vagus nerves) and to circumventricular organs, including the subfornical organ and area postrema, via a humoral pathway (blood/cerebrospinal fluid). Circuits are formed that stimulate or inhibit homeostatic Na intake involving participation of the parabrachial nucleus, pre-locus coeruleus, medial tuberomammillary nuclei, median eminence, par-aventricular and supraoptic nuclei, and other structures with reward properties such as the bed nucleus of the stria terminalis, central amygdala, and ventral tegmental area. Finally, the kidney uses neural signals (e.g., renal sympathetic nerves) and vascular (e.g., renal perfusion pressure) and humoral (e.g., renin-angiotensin-aldosterone system, cardiac natriuretic peptides, antidiuretic hormone , and oxytocin) factors to promote Na excretion or retention and thereby maintain extracellular fluid volume. All these intake and excretion processes are modulated by chemical messengers, many of which (e.g., aldosterone, angiotensin II, and oxytocin) have effects that are coordinated at peripheral and central level to ensure Na homeostasis.
