Paraventricular nucleus: a site for the integration of neuroendocrine and autonomic mechanisms

Navigating Central Oxytocin Transport: Known Realms and Uncharted Territories

Complex mechanisms govern the transport and action of oxytocin (Oxt), a neuropeptide and hormone that mediates diverse physiologic processes. While Oxt exerts site-specific and rapid effects in the brain via axonal and somatodendritic release, volume transmission via CSF and the neurovascular interface can act as an additional mechanism to distribute Oxt signals across distant brain regions on a slower timescale. This review focuses on modes of Oxt transport and action in the CNS, with particular emphasis on the roles of perivascular spaces, the blood-brain barrier (BBB), and circumventricular organs in coordinating the triadic interaction among circulating blood, CSF, and parenchyma. Perivascular spaces, critical conduits for CSF flow, play a pivotal role in Oxt diffusion and distribution within the CNS and reciprocally undergo Oxt-mediated structural and functional reconstruction. While the BBB modulates the movement of Oxt between systemic and cerebral circulation in a majority of brain regions, circumventricular organs without a functional BBB can allow for diffusion, monitoring, and feedback regulation of bloodborne peripheral signals such as Oxt. Recognition of these additional transport mechanisms provides enhanced insight into the systemic propagation and regulation of Oxt activity.

Sexually dimorphic distribution of Kiss1 neurons in the bed nucleus of the stria terminalis

Kiss1 neurons play a crucial role in reproductive function and are found in distinct brain regions, including the bed nucleus of the stria terminalis (BNST). However, the sexual dimorphism of Kiss1 neurons in the BNST and their projections has not been fully characterized. This study examined the distribution and projections of Kiss1 neurons in the anterior (aBNST) and principal (prBNST) regions of the BNST in male and female Kiss1-Cre and Kiss1-Cre; tdTomatoloxP/+ mice. Neuroanatomical analysis and tracing experiments were conducted to quantify Kiss1 neurons and map their projections. Males had approximately a threefold higher number of Kiss1 neurons in the prBNST than females, while no significant sex difference was observed in the aBNST. Viral tracing experiments revealed sexually dimorphic projections of Kiss1adBNST neurons, with females displaying more diverse projections to various brain regions involved in reproduction and social behaviors. Kiss1prBNST neurons project exclusively to the zona incerta and adBNST in both sexes, while females exhibited additional projections to the RP3V and PVH. The sexually dimorphic distribution and projections of Kiss1BNST neurons suggest their potential role in modulating sex-specific behaviors and neuroendocrine functions. This neuroanatomical sexual dimorphism may contribute to sex differences in social and reproductive behaviors associated with BNST function, providing new insights into the neural basis of sex-specific behaviors and reproductive regulation.

Postnatal hyperosmolality alters development of hypothalamic feeding circuits with context-specific changes in ingestive behavior

Drinking and feeding are tightly coordinated homeostatic events and the paraventricular nucleus of the hypothalamus (PVH) represents a possible node of neural integration for signals related to energy and fluid homeostasis. We used TRAP2;Ai14 mice and Fos labeling to visualize neurons in the PVH and median preoptic nucleus (MEPO) responding to both water deprivation and feeding signals. We determined that structural and functional development of dehydration-sensitive inputs to the PVH precedes those of agouti-related peptide (AgRP) neurons, which convey hunger signals and are known to be developmentally programmed by nutrition. Moreover, we found that osmotic hyperstimulation of neonatal mice led to enhanced AgRP inputs to the PVH in adulthood, as well as disruptions to ingestive behaviors during high-fat diet feeding and dehydration-anorexia. Thus, development of feeding circuits is impacted not only by nutritional signals, but also by early perturbations to fluid homeostasis with context-specific consequences for coordination of ingestive behavior.

Single-cell genomics meets systems neuroscience: Insights from mapping the brain circuitry of stress

Responses to external and internal dangers is essential for survival and homeostatic regulation. Hypothalamic corticotropin-releasing hormone neurons (CRHNs) play a pivotal role in regulating neuroendocrine responses to fear and stress. In recent years, the application of neurogenetic tools, such as fiber photometry, chemogenetics and optogenetics, have provided new insights into the dynamic neuronal responses of CRHNs during stressful events, offering new perspectives into their functional significance in mediating neurobehavioural responses to stress. Transsynaptic viral tracers have facilitated the comprehensive mapping of neuronal inputs to CRHNs. Furthermore, the development and application of innovative single-cell genomic tools combined with viral tracing have begun to pave the way for a deeper understanding of the transcriptional profiles of neural circuit components, enabling molecular-anatomical circuit mapping. Here, I will discuss how these systems neuroscience approaches and novel single-cell genomic methods are advancing the molecular and functional mapping of stress neurocircuits, their associated challenges and future directions.

Development of catecholaminergic neurons of Otp-lineage in the medial extended amygdala and related forebrain centers

Catecholaminergic (CA) neurons of the medial extended amygdala, preoptic region and adjacent alar hypothalamus have been involved in different aspects of social behavior, as well as in modulation of homeostasis in response to different stressors. Previous data suggested that at least some CA neurons of the medial extended amygdala could originate in a hypothalamic embryonic domain that expresses the transcription factor Otp. To investigate this, we used Otp-eGFP mice (with permanent labeling of GFP in Otp cells) to analyze coexpression of GFP and tyrosine hydroxylase (TH) throughout ontogenesis by way of double immunofluorescence. Our results provide evidence that some forebrain CA cells belong to the Otp lineage. In particular, we found small subpopulations of TH cells that coexpress GFP within the medial extended amygdala, the periventricular preoptic area, the paraventricular hypothalamus, the periventricular hypothalamus, as well as some subdivisions of the basal hypothalamus. In some of the Otp cells, such as those of extended amygdala, the expression of TH appears to be transitory, in agreement with previous studies. The results open interesting questions about the role of these Otp versus non-Otp catecholaminergic subpopulations during development, network integration and in modulation of different functions, including homeostasis and social behaviors.

Structural and functional alterations in hypothalamic subregions in male patients with alcohol use disorder

BACKGROUND

The hypothalamus is involved in stress regulation and reward processing, with its various nuclei exhibiting unique functions and connections. However, human neuroimaging studies on the hypothalamic subregions are limited in drug addiction. This study examined the volumes and functional connectivity of hypothalamic subregions in individuals with alcohol use disorder (AUD).

METHOD

The study included 24 male patients with AUD who had maintained abstinence and 24 healthy male controls, all of whom underwent brain structural and resting-state functional magnetic resonance imaging. The hypothalamus was segmented into five subunits using a deep learning-based algorithm, with comparisons of volumes and functional connectivity (FC) between the two groups. The relationships between these measures and alcohol-related characteristics were examined in the AUD group.

RESULTS

Findings indicated lower volumes in the anterior-superior (corrected-p < 0.001) and tuberal-superior subunits (corrected-p = 0.002) and altered FC of these and the anterior-inferior subunit among AUD patients (corrected-p < 0.05). Moreover, greater disease severity and a longer history of heavy drinking correlated with lower volumes in the anterior-superior (r = -0.42, p = 0.045) and tuberal-superior subregions (r = -0.61, p = 0.013), respectively. Conversely, a longer abstinence duration was associated with larger volumes in the anterior-superior (r = 0.56, p = 0.008) and tuberal-superior subunits (r = 0.40, p = 0.048) and with higher FC between the tuberal-superior hypothalamus and the thalamus, caudate, and anterior cingulate cortex (r = 0.55, p = 0.014).

CONCLUSIONS

Our results suggest that specific regional alterations within the hypothalamus, particularly the superior subregions, are associated with AUD, and more importantly, that these alterations may be reversible with prolonged abstinence.

Downregulation of neuronal nitric oxide synthase (nNOS) within the paraventricular nucleus in Ins2Akita-type-1 diabetic mice contributes to sympatho-excitation

Activation of both renin-angiotensin system (RAS) and the sympathetic system is the primary etiologic event in developing cardiovascular complications in diabetes mellitus (DM). However, the precise mechanisms for sympathetic activation in DM have not been elucidated. Here we attempted to investigate diabetes-linked cardiovascular dysregulation due to angiotensin II (Ang II)-mediated reduction in neuronal nitric oxide (NO) synthase (nNOS) within the paraventricular neuleus (PVN). In the present study, we used Ins2+/-Akita (a spontaneous, insulin-dependent genetic diabetic non-obese murine model) and wild-type (WT) littermates mice as controls. At 14 weeks of age, we found the Akita mice had increased renal sympathetic nerve activity and elevated levels of plasma norepinephrine. There was decreased expression of nNOS protein (Akita 0.43 ± 0.11 vs. WT 0.75 ± 0.05, P < 0.05) in the PVN of Akita mice. Akita mice had increased expression of angiotensin-converting enzyme (ACE) (Akita 0.58 ± 0.05 vs. WT 0.34 ± 0.04, P < 0.05) and Ang II type 1 receptor (Akita 0.49 ± 0.03 vs. WT 0.29 ± 0.09, P < 0.05), decreased expressions of ACE2 (Akita 0.17 ± 0.05 vs. WT 0.27 ± 0.03, P < 0.05) and angiotensin (1-7) Mas receptor (Akita 0.46 ± 0.02 vs. WT 0.77 ± 0.07, P < 0.05). Futher, there were increased protein levels of protein inhibitor of nNOS (PIN) (Akita 1.75 ± 0.08 vs. WT 0.71 ± 0.09, P < 0.05) with concomitantly decreased catalytically active dimers of nNOS (Akita 0.11 ± 0.04 vs. WT 0.19 ± 0.02, P < 0.05) in the PVN in Akita mice. Our studies suggest that activation of the excitatory arm of RAS, leads to a decrease NO, causing an over-activation of the sympathetic drive in DM.

Insulin activates parasympathetic hepatic-related neurons of the paraventricular nucleus of the hypothalamus through mTOR signaling

Integration of autonomic and metabolic regulation, including hepatic function, is a critical role played by the brain's hypothalamic region. Specifically, the paraventricular nucleus of the hypothalamus (PVN) regulates autonomic functions related to metabolism, such as hepatic glucose production. Although insulin can act directly on hepatic tissue to inhibit hepatic glucose production, recent evidence implicates that central actions of insulin within PVN also regulate glucose metabolism. However, specific central circuits responsible for insulin signaling with relation to hepatic regulation are poorly understood. As a heterogeneous nucleus essential to controlling parasympathetic motor output with notable expression of insulin receptors, PVN is an appealing target for insulin-dependent modulation of parasympathetic activity. Here, we tested the hypothesis that insulin activates hepatic-related PVN (PVNhepatic) neurons through a parasympathetic pathway. Using transsynaptic retrograde tracing, labeling within PVN was first identified 24 h after its expression in the dorsal motor nucleus of the vagus (DMV) and 72 h after hepatic injection. Critically, nearly all labeling in medial PVN was abolished after a left vagotomy, indicating that PVNhepatic neurons in this region are part of a central circuit innervating parasympathetic motor neurons. Insulin also significantly increased the firing frequency of PVNhepatic neurons in this subregion. Mechanistically, rapamycin pretreatment inhibited insulin-dependent activation of PVNhepatic neurons. Therefore, central insulin signaling can activate a subset of PVNhepatic neurons that are part of a unique parasympathetic network in control of hepatic function. Taken together, PVNhepatic neurons related to parasympathetic output regulation could serve as a key central network in insulin's ability to control hepatic functions.NEW & NOTEWORTHY Increased peripheral insulin concentrations are known to decrease hepatic glucose production through both direct actions on hepatocytes and central autonomic networks. Despite this understanding, how (and in which brain regions) insulin exerts its action is still obscure. Here, we demonstrate that insulin activates parasympathetic hepatic-related PVN neurons (PVNhepatic) and that this effect relies on mammalian target of rapamycin (mTOR) signaling, suggesting that insulin modulates hepatic function through autonomic pathways involving insulin receptor intracellular signaling cascades.

Modulation of stress-related behaviour by preproglucagon neurons and hypothalamic projections to the nucleus of the solitary tract

Stress-induced behaviours are driven by complex neural circuits and some neuronal populations concurrently modulate diverse behavioural and physiological responses to stress. Glucagon-like peptide-1 (GLP-1)-producing preproglucagon (PPG) neurons within the lower brainstem caudal nucleus of the solitary tract (cNTS) are particularly sensitive to stressful stimuli and are implicated in multiple physiological and behavioural responses to interoceptive and psychogenic threats. However, the afferent inputs driving stress-induced activation of PPG neurons are largely unknown, and the role of PPG neurons in anxiety-like behaviour is controversial. Through chemogenetic manipulations we reveal that cNTS PPG neurons have the ability to moderately increase anxiety-like behaviours in mice in a sex-dependent manner. Using an intersectional approach, we show that input from the paraventricular nucleus of the hypothalamus (PVN) drives activation of both the cNTS as a whole and PPG neurons in particular in response to acute restraint stress, but that while this input is rich in corticotropin-releasing hormone (CRH), PPG neurons do not express significant levels of receptors for CRH and are not activated following lateral ventricle delivery of CRH. Finally, we demonstrate that cNTS-projecting PVN neurons are necessary for the ability of restraint stress to suppress food intake in male mice. Our findings reveal sex differences in behavioural responses to PPG neural activation and highlight a hypothalamic-brainstem pathway in stress-induced hypophagia.

Modeling craniopharyngioma for drug screening reveals a neuronal mechanism for tumor growth

Tumors occurring along the hypothalamus-pituitary axis receive axonal projection from neuroendocrine neurons, but it remains unclear whether neuroendocrine neuronal activity drives tumor expansion. Craniopharyngioma is a common suprasellar tumor with a propensity for invading the hypothalamus, leading to devastating endocrine and metabolic disorders. Here, we developed two autochthonous animal models that faithfully recapitulate the molecular pathology, clinical manifestations, and transcriptomic profiles of papillary craniopharyngioma. Using high-throughput drug screening, we identified 74 compounds with potent antitumor efficacy. The administration of (S)-amlodipine besylate achieved tumor regression in vivo, potentially by abrogating calcium transients and neuron-to-tumor chemical transmission. Chemogenetic manipulation of neuroendocrine neuronal activity bidirectionally regulated tumor cell growth in our mouse model, suggesting that craniopharyngioma hijacks hypothalamic neurons to promote tumor progression. These findings deepen our understanding of suprasellar tumor biology and offer promising avenues for clinical exploration of effective chemotherapies.

AgRP neurons mediate activity-dependent development of oxytocin connectivity and autonomic regulation

During postnatal life, leptin specifies neuronal inputs to the paraventricular nucleus of the hypothalamus (PVH) and activates agouti-related peptide (AgRP) neurons in the arcuate nucleus of the hypothalamus. Activity-dependent developmental mechanisms impact refinement of sensory circuits, but whether leptin-mediated postnatal neuronal activity specifies hypothalamic neural projections is largely unexplored. Here, we used chemogenetics to manipulate the activity of AgRP neurons during a discrete postnatal critical period and evaluated the development of AgRP inputs to the PVH and descending efferent outflow to the dorsal vagal complex (DVC). In leptin-deficient mice, targeting of AgRP neuronal outgrowth to PVH oxytocin neurons was reduced, and despite the lack of leptin receptors found on oxytocin neurons in the PVH, oxytocin-containing connections to the DVC were also impaired. Activation of AgRP neurons during early postnatal life not only normalized AgRP inputs to the PVH but also oxytocin outputs to the DVC in leptin-deficient mice. Blocking AgRP neuron activity during the same postnatal period reduced the density of AgRP inputs to the PVH of wild type mice, as well as the density of oxytocin-containing DVC fibers, and these innervation deficits were associated with dysregulated autonomic function. These findings suggest that leptin-mediated AgRP neuronal activity is required for the development of PVH connectivity and represents a unique activity-dependent mechanism for specification of neural pathways involved in the hypothalamic integration of autonomic responses.

Early perturbations to fluid homeostasis alter development of hypothalamic feeding circuits with context-specific changes in ingestive behavior

Drinking and feeding are tightly coordinated homeostatic events and the paraventricular nucleus of the hypothalamus (PVH) represents a possible node of neural integration for signals related to energy and fluid homeostasis. We used TRAP2;Ai14 and Fos labeling to visualize neurons in the PVH and median preoptic nucleus (MEPO) responding to both water deprivation and hunger. Moreover, we determined that structural and functional development of dehydration-sensitive inputs to the PVH from the MEPO precedes those of agouti-related peptide (AgRP) neurons, which convey hunger signals and are known to be developmentally programmed by nutrition. We also determined that osmotic hyperstimulation of neonatal mice led to enhanced AgRP inputs to the PVH in adulthood, as well as disruptions to ingestive behaviors during high-fat diet feeding and dehydration-anorexia. Thus, development of feeding circuits is impacted not only by nutritional signals, but also by early perturbations to fluid homeostasis with context-specific consequences for coordination of ingestive behavior.

Renal interoception in health and disease

Catheter based renal denervation has recently been FDA approved for the treatment of hypertension. Traditionally, the anti-hypertensive effects of renal denervation have been attributed to the ablation of the efferent sympathetic renal nerves. In recent years the role of the afferent sensory renal nerves in the regulation of blood pressure has received increased attention. In addition, afferent renal denervation is associated with reductions in sympathetic nervous system activity. This suggests that reductions in sympathetic drive to organs other than the kidney may contribute to the non-renal beneficial effects observed in clinical trials of catheter based renal denervation. In this review we will provide an overview of the role of the afferent renal nerves in the regulation of renal function and the development of pathophysiologies, both renal and non-renal. We will also describe the central projections of the afferent renal nerves, to give context to the responses seen following their ablation and activation. Finally, we will discuss the emerging role of the kidney as an interoceptive organ. We will describe the potential role of the kidney in the regulation of interoceptive sensitivity and in this context, speculate on the possible pathological consequences of altered renal function.

Role of stress and early-life stress in the pathogeny of inflammatory bowel disease

Numerous preclinical and clinical studies have shown that stress is one of the main environmental factor playing a significant role in the pathogeny and life-course of bowel diseases. However, stressful events that occur early in life, even during the fetal life, leave different traces within the central nervous system, in area involved in stress response and autonomic network but also in emotion, cognition and memory regulation. Early-life stress can disrupt the prefrontal-amygdala circuit thus favoring an imbalance of the autonomic nervous system and the hypothalamic-pituitary adrenal axis, resulting in anxiety-like behaviors. The down regulation of vagus nerve and cholinergic anti-inflammatory pathway favors pro-inflammatory conditions. Recent data suggest that emotional abuse at early life are aggravating risk factors in inflammatory bowel disease. This review aims to unravel the mechanisms that explain the consequences of early life events and stress in the pathophysiology of inflammatory bowel disease and their mental co-morbidities. A review of therapeutic potential will also be covered.

AgRP neurons mediate activity-dependent development of oxytocin connectivity and autonomic regulation

During postnatal life, the adipocyte-derived hormone leptin is required for proper targeting of neural inputs to the paraventricular nucleus of the hypothalamus (PVH) and impacts the activity of neurons containing agouti-related peptide (AgRP) in the arcuate nucleus of the hypothalamus. Activity-dependent developmental mechanisms are known to play a defining role during postnatal organization of neural circuits, but whether leptin-mediated postnatal neuronal activity specifies neural projections to the PVH or impacts downstream connectivity is largely unexplored. Here, we blocked neuronal activity of AgRP neurons during a discrete postnatal period and evaluated development of AgRP inputs to defined regions in the PVH, as well as descending projections from PVH oxytocin neurons to the dorsal vagal complex (DVC) and assessed their dependence on leptin or postnatal AgRP neuronal activity. In leptin-deficient mice, AgRP inputs to PVH neurons were significantly reduced, as well as oxytocin-specific neuronal targeting by AgRP. Moreover, downstream oxytocin projections from the PVH to the DVC were also impaired, despite the lack of leptin receptors found on PVH oxytocin neurons. Blocking AgRP neuron activity specifically during early postnatal life reduced the density of AgRP inputs to the PVH, as well as the density of projections from PVH oxytocin neurons to the DVC, and these innervation deficits were associated with dysregulated autonomic function. These findings suggest that postnatal targeting of descending PVH oxytocin projections to the DVC requires leptin-mediated AgRP neuronal activity, and represents a novel activity-dependent mechanism for hypothalamic specification of metabolic circuitry, with consequences for autonomic regulation.

Significance statement

Hypothalamic neural circuits maintain homeostasis by coordinating endocrine signals with autonomic responses and behavioral outputs to ensure that physiological responses remain in tune with environmental demands. The paraventricular nucleus of the hypothalamus (PVH) plays a central role in metabolic regulation, and the architecture of its neural inputs and axonal projections is a defining feature of how it receives and conveys neuroendocrine information. In adults, leptin regulates multiple aspects of metabolic physiology, but it also functions during development to direct formation of circuits controlling homeostatic functions. Here we demonstrate that leptin acts to specify the input-output architecture of PVH circuits through an activity-dependent, transsynaptic mechanism, which represents a novel means of sculpting neuroendocrine circuitry, with lasting effects on how the brain controls energy balance.

The Surgical Stress Response and Anesthesia: A Narrative Review

The human physiological response "to stress" includes all metabolic and hormonal changes produced by a traumatic event at the micro or macro cellular levels. The main goal of the body's first response to trauma is to keep physiological homeostasis. The perioperative non-specific adaptation response can sometimes be detrimental and can produce systemic inflammatory response syndrome (SIRS), characterized by hypermetabolism and hyper catabolism. We performed a narrative review consisting of a description of the surgical stress response's categories of changes (neurohormonal and immunological response) followed by reviewing methods found in published studies to modulate the surgical stress response perioperatively. We described various preoperative measures cited in the literature as lowering the burden of surgical trauma. This article revises the anesthetic drugs and techniques that have an impact on the surgical stress response and proven immune-modulatory effects. We also tried to name present knowledge gaps requiring future research. Our review concludes that proper preoperative measures, adequate general anesthetics, multimodal analgesia, early postoperative mobilization, and early enteral nutrition can decrease the stress response to surgery and ease patient recovery. Anesthetics and analgesics used during the perioperative period may modulate the innate and adaptive immune system and inflammatory system, with a consecutive impact on cancer recurrence and long-term outcomes.

Single-neuron projectomes of mouse paraventricular hypothalamic nucleus oxytocin neurons reveal mutually exclusive projection patterns

Oxytocin (OXT) plays important roles in autonomic control and behavioral modulation. However, it is unknown how the projection patterns of OXT neurons align with underlying physiological functions. Here, we present the reconstructed single-neuron, whole-brain projectomes of 264 OXT neurons of the mouse paraventricular hypothalamic nucleus (PVH) at submicron resolution. These neurons hierarchically clustered into two groups, with distinct morphological and transcriptional characteristics and mutually exclusive projection patterns. Cluster 1 (177 neurons) axons terminated exclusively in the median eminence (ME) and have few collaterals terminating within hypothalamic regions. By contrast, cluster 2 (87 neurons) sent wide-spread axons to multiple brain regions, but excluding ME. Dendritic arbors of OXT neurons also extended outside of the PVH, suggesting capability to sense signals and modulate target regions. These single-neuron resolution observations reveal distinct OXT subpopulations, provide comprehensive analysis of their morphology, and lay the structural foundation for better understanding the functional heterogeneity of OXT neurons.

Validity of mental and physical stress models

Different stress models are employed to enhance our understanding of the underlying mechanisms and explore potential interventions. However, the utility of these models remains a critical concern, as their validities may be limited by the complexity of stress processes. Literature review revealed that both mental and physical stress models possess reasonable construct and criterion validities, respectively reflected in psychometrically assessed stress ratings and in activation of the sympathoadrenal system and the hypothalamic-pituitary-adrenal axis. The findings are less robust, though, in the pharmacological perturbations' domain, including such agents as adenosine or dobutamine. Likewise, stress models' convergent- and discriminant validity vary depending on the stressors' nature. Stress models share similarities, but also have important differences regarding their validities. Specific traits defined by the nature of the stressor stimulus should be taken into consideration when selecting stress models. Doing so can personalize prevention and treatment of stress-related antecedents, its acute processing, and chronic sequelae. Further work is warranted to refine stress models' validity and customize them so they commensurate diverse populations and circumstances.

Peripheral oxytocin levels are linked to hypothalamic gray matter volume in autistic adults: a cross-sectional secondary data analysis

Oxytocin (OXT) is known to modulate social behavior and cognition and has been discussed as pathophysiological and therapeutic factor for autism spectrum disorder (ASD). An accumulating body of evidence indicates the hypothalamus to be of particular importance with regard to the underlying neurobiology. Here we used a region of interest voxel-based morphometry (VBM) approach to investigate hypothalamic gray matter volume (GMV) in autistic (n = 29, age 36.03 ± 11.0) and non-autistic adults (n = 27, age 30.96 ± 11.2). Peripheral plasma OXT levels and the autism spectrum quotient (AQ) were used for correlation analyses. Results showed no differences in hypothalamic GMV in autistic compared to non-autistic adults but suggested a differential association between hypothalamic GMV and OXT levels, such that a positive association was found for the ASD group. In addition, hypothalamic GMV showed a positive association with autistic traits in the ASD group. Bearing in mind the limitations such as a relatively small sample size, a wide age range and a high rate of psychopharmacological treatment in the ASD sample, these results provide new preliminary evidence for a potentially important role of the HTH in ASD and its relationship to the OXT system, but also point towards the importance of interindividual differences.

Inactivation of the paraventricular nucleus attenuates the cardiogenic sympathetic afferent reflex in the spontaneously hypertensive rat

BACKGROUND

Myocardial ischemia causes the release of bradykinin, which stimulates cardiac afferents, causing sympathetic excitation and chest pain. Glutamatergic activation of the paraventricular hypothalamic nucleus (PVN) in the spontaneously hypertensive rat (SHR) drives elevated basal sympathetic activity. Thus, we tested the hypothesis that inactivation of the PVN attenuates the elevated reflex response to epicardial bradykinin in the SHR and that ionotropic PVN glutamate receptors mediate the elevated reflex.

METHODS

We recorded the arterial pressure and renal sympathetic nerve activity (RSNA) response to epicardial bradykinin application in anesthetized SHR and Wistar Kyoto (WKY) rats before and after PVN microinjection of GABA A agonist muscimol or ionotropic glutamate receptor antagonist kynurenic acid.

RESULTS

Muscimol significantly decreased the arterial pressure response to bradykinin from 180.4 ± 5.8 to 119.5 ± 6.9 mmHg in the SHR and from 111.8 ± 7.0 to 84.2 ± 8.3 mmHg in the WKY and the RSNA response from 186.2 ± 7.1 to 142.7 ± 7.3% of baseline in the SHR and from 201.0 ± 11.5 to 160.2 ± 9.3% of baseline in the WKY. Kynurenic acid significantly decreased the arterial pressure response in the SHR from 164.5 ± 5.0 to 126.2 ± 7.7 mmHg and the RSNA response from 189.9 ± 13.7to 168.5 ± 12.7% of baseline but had no effect in the WKY.

CONCLUSION

These results suggest that tonic PVN activity is critical for the full manifestation of the CSAR in both the WKY and SHR. Glutamatergic PVN activity contributes to the augmented CSAR observed in the SHR.

The Role of Central Oxytocin in Autonomic Regulation

Oxytocin (OXT), a neuropeptide originating from the hypothalamus and traditionally associated with peripheral functions in parturition and lactation, has emerged as a pivotal player in the central regulation of the autonomic nervous system (ANS). This comprehensive ANS, comprising sympathetic, parasympathetic, and enteric components, intricately combines sympathetic and parasympathetic influences to provide unified control. The central oversight of sympathetic and parasympathetic outputs involves a network of interconnected regions spanning the neuroaxis, playing a pivotal role in the real-time regulation of visceral function, homeostasis, and adaptation to challenges. This review unveils the significant involvement of the central OXT system in modulating autonomic functions, shedding light on diverse subpopulations of OXT neurons within the paraventricular nucleus of the hypothalamus and their intricate projections. The narrative progresses from the basics of central ANS regulation to a detailed discussion of the central controls of sympathetic and parasympathetic outflows. The subsequent segment focuses specifically on the central OXT system, providing a foundation for exploring the central role of OXT in ANS regulation. This review synthesizes current knowledge, paving the way for future research endeavors to unravel the full scope of autonomic control and understand multifaceted impact of OXT on physiological outcomes.

Hindbrain Adrenergic/Noradrenergic Control of Integrated Endocrine and Autonomic Stress Responses

Hindbrain adrenergic/noradrenergic nuclei facilitate endocrine and autonomic responses to physical and psychological challenges. Neurons that synthesize adrenaline and noradrenaline target hypothalamic structures to modulate endocrine responses while descending spinal projections regulate sympathetic function. Furthermore, these neurons respond to diverse stress-related metabolic, autonomic, and psychosocial challenges. Accordingly, adrenergic and noradrenergic nuclei are integrative hubs that promote physiological adaptation to maintain homeostasis. However, the precise mechanisms through which adrenaline- and noradrenaline-synthesizing neurons sense interoceptive and exteroceptive cues to coordinate physiological responses have yet to be fully elucidated. Additionally, the regulatory role of these cells in the context of chronic stress has received limited attention. This mini-review consolidates reports from preclinical rodent studies on the organization and function of brainstem adrenaline and noradrenaline cells to provide a framework for how these nuclei coordinate endocrine and autonomic physiology. This includes identification of hindbrain adrenaline- and noradrenaline-producing cell groups and their role in stress responding through neurosecretory and autonomic engagement. Although temporally and mechanistically distinct, the endocrine and autonomic stress axes are complementary and interconnected. Therefore, the interplay between brainstem adrenergic/noradrenergic nuclei and peripheral physiological systems is necessary for integrated stress responses and organismal survival.

Taste receptor type 1 member 3 enables western diet-induced anxiety in mice

BACKGROUND

Accumulating evidence supports that the Western diet (WD), a diet high in saturated fat and sugary drinks, contributes to the pathogenesis of anxiety disorders, which are the most prevalent mental disorders worldwide. However, the underlying mechanisms by which WD causes anxiety remain unclear. Abundant expression of taste receptor type 1 member 3 (TAS1R3) has been identified in the hypothalamus, a key brain area involved in sensing peripheral nutritional signals and regulating anxiety. Thus, we investigated the influence of excessive WD intake on anxiety and mechanisms by which WD intake affects anxiety development using wild-type (WT) and Tas1r3 deficient (Tas1r3-/-) mice fed a normal diet (ND) or WD for 12 weeks.

RESULTS

WD increased anxiety in male WT mice, whereas male Tas1r3-/- mice were protected from WD-induced anxiety, as assessed by open field (OF), elevated plus maze (EPM), light-dark box (LDB), and novelty-suppressed feeding (NSF) tests. Analyzing the hypothalamic transcriptome of WD-fed WT and Tas1r3-/- mice, we found 1,432 genes significantly up- or down-regulated as a result of Tas1r3 deficiency. Furthermore, bioinformatic analysis revealed that the CREB/BDNF signaling-mediated maintenance of neuronal regeneration, which can prevent anxiety development, was enhanced in WD-fed Tas1r3-/- mice compared with WD-fed WT mice. Additionally, in vitro studies further confirmed that Tas1r3 knockdown prevents the suppression of Creb1 and of CREB-mediated BDNF expression caused by high levels of glucose, fructose, and palmitic acid in hypothalamic neuronal cells.

CONCLUSIONS

Our results imply that TAS1R3 may play a key role in WD-induced alterations in hypothalamic functions, and that inhibition of TAS1R3 overactivation in the hypothalamus could offer therapeutic targets to alleviate the effects of WD on anxiety.

Defensive responses: behaviour, the brain and the body

Most animals live under constant threat from predators, and predation has been a major selective force in shaping animal behaviour. Nevertheless, defence responses against predatory threats need to be balanced against other adaptive behaviours such as foraging, mating and recovering from infection. This behavioural balance in ethologically relevant contexts requires adequate integration of internal and external signals in a complex interplay between the brain and the body. Despite this complexity, research has often considered defensive behaviour as entirely mediated by the brain processing threat-related information obtained via perception of the external environment. However, accumulating evidence suggests that the endocrine, immune, gastrointestinal and reproductive systems have important roles in modulating behavioural responses to threat. In this Review, we focus on how predatory threat defence responses are shaped by threat imminence and review the circuitry between subcortical brain regions involved in mediating defensive behaviours. Then, we discuss the intersection of peripheral systems involved in internal states related to infection, hunger and mating with the neurocircuits that underlie defence responses against predatory threat. Through this process, we aim to elucidate the interconnections between the brain and body as an integrated network that facilitates appropriate defensive responses to threat and to discuss the implications for future behavioural research.

High-calorie diets uncouple hypothalamic oxytocin neurons from a gut-to-brain satiation pathway via κ-opioid signaling

Oxytocin-expressing paraventricular hypothalamic neurons (PVNOT neurons) integrate afferent signals from the gut, including cholecystokinin (CCK), to adjust whole-body energy homeostasis. However, the molecular underpinnings by which PVNOT neurons orchestrate gut-to-brain feeding control remain unclear. Here, we show that mice undergoing selective ablation of PVNOT neurons fail to reduce food intake in response to CCK and develop hyperphagic obesity on a chow diet. Notably, exposing wild-type mice to a high-fat/high-sugar (HFHS) diet recapitulates this insensitivity toward CCK, which is linked to diet-induced transcriptional and electrophysiological aberrations specifically in PVNOT neurons. Restoring OT pathways in diet-induced obese (DIO) mice via chemogenetics or polypharmacology sufficiently re-establishes CCK's anorexigenic effects. Last, by single-cell profiling, we identify a specialized PVNOT neuronal subpopulation with increased κ-opioid signaling under an HFHS diet, which restrains their CCK-evoked activation. In sum, we document a (patho)mechanism by which PVNOT signaling uncouples a gut-brain satiation pathway under obesogenic conditions.

Modulating activity of PVN neurons prevents atrial fibrillation induced circulation dysfunction by electroacupuncture at BL15

BACKGROUND

Circulation dysfunction is a major contributing factor to thrombosis in patients with atrial fibrillation (AF) for which effective interventions are lacking. Growing evidence indicates that regulating the paraventricular nucleus (PVN), an autonomic control center, could offer a novel strategy for treating cardiovascular and circulatory diseases. Concurrently, electroacupuncture (EA) at Xinshu (BL15), a form of peripheral nerve stimulation, has shown efficacy in treating several cardiovascular conditions, although its specific mechanism remains unclear. This study aimed to assess the impact of EA at BL15 on circulatory dysfunction in a rat AF model and investigate the pivotal role of PVN neuronal activity.

METHODS

To mimic the onset of AF, male SD rats received tail intravenous injection of ACh-CaCl2 and were then subjected to EA at BL15, sham EA, or EA at Shenshu (BL23). Macro- and micro-circulation function were evaluated using in vivo ultrasound imaging and laser doppler testing, respectively. Vasomotricity was assessed by measuring dimension changes during vascular relaxation and contraction. Vascular endothelial function was measured using myograph, and the activation of the autonomic nerve system was evaluated through nerve activity signals. Additionally, chemogenetic manipulation was used to block PVN neuronal activation to further elucidate the role of PVN activation in the prevention of AF-induced blood circulation dysfunction through EA treatment.

RESULTS

Our data demonstrate that EA at BL15, but not BL23 or sham EA, effectively prevented AF-induced macro- and micro-circulation dysfunction. Furthermore, EA at BL15 restored AF-induced vasomotricity impairment. Additionally, EA treatment prevented abnormal activation of the autonomic nerve system induced by AF, although it did not address vascular endothelial dysfunction. Importantly, excessive activation of PVN neurons negated the protective effects of EA treatment on AF-induced circulation dysfunction in rats.

CONCLUSION

These results indicate that EA treatment at BL15 modulates PVN neuronal activity and provides protection against AF-induced circulatory dysfunction.

Heralding a new era of oxytocinergic research: New tools, new problems?

According to classic neuroendocrinology, hypothalamic oxytocin cells can be categorized into parvo- and magnocellular neurons. However, research in the last decade provided ample evidence that this black-and-white model of oxytocin neurons is most likely oversimplified. Novel genetic, functional and morphological studies indicate that oxytocin neurons might be organized in functional modules and suggest the existence of five or more distinct oxytocinergic subpopulations. However, many of these novel, automated high-throughput techniques might be inherently biased and interpretation of acquired data needs to be approached with caution to enable drawing sound and reliable conclusions. In addition, the recent finding that astrocytes in various brain regions express functional oxytocin receptors represents a paradigm shift and challenges the view that oxytocin primarily acts as a direct peptidergic neurotransmitter. This review highlights the latest technical advances in oxytocinergic research, puts recent studies on the oxytocin system into context and formulates various provocative ideas based on novel findings that challenges various prevailing hypotheses and dogmas about oxytocinergic modulation.

The locus coeruleus contributes to the anorectic, nausea, and autonomic physiological effects of glucagon-like peptide-1

Increasing the therapeutic potential and reducing the side effects of U.S. Food and Drug Administration-approved glucagon-like peptide-1 receptor (GLP-1R) agonists used to treat obesity require complete characterization of the central mechanisms that mediate both the food intake-suppressive and illness-like effects of GLP-1R signaling. Our studies, in the rat, demonstrate that GLP-1Rs in the locus coeruleus (LC) are pharmacologically and physiologically relevant for food intake control. Furthermore, agonism of LC GLP-1Rs induces illness-like behaviors, and antagonism of LC GLP-1Rs can attenuate GLP-1R-mediated nausea. Electrophysiological and behavioral pharmacology data support a role for LC GLP-1Rs expressed on presynaptic glutamatergic terminals in the control of feeding and malaise. Collectively, our work establishes the LC as a site of action for GLP-1 signaling and extends our understanding of the GLP-1 signaling mechanism necessary for the development of improved obesity pharmacotherapies.

Neural Progenitor Cells and the Hypothalamus

Neural progenitor cells (NPCs) are multipotent neural stem cells (NSCs) capable of self-renewing and differentiating into neurons, astrocytes and oligodendrocytes. In the postnatal/adult brain, NPCs are primarily located in the subventricular zone (SVZ) of the lateral ventricles (LVs) and subgranular zone (SGZ) of the hippocampal dentate gyrus (DG). There is evidence that NPCs are also present in the postnatal/adult hypothalamus, a highly conserved brain region involved in the regulation of core homeostatic processes, such as feeding, metabolism, reproduction, neuroendocrine integration and autonomic output. In the rodent postnatal/adult hypothalamus, NPCs mainly comprise different subtypes of tanycytes lining the wall of the 3^rd ventricle. In the postnatal/adult human hypothalamus, the neurogenic niche is constituted by tanycytes at the floor of the 3^rd ventricle, ependymal cells and ribbon cells (showing a gap-and-ribbon organization similar to that in the SVZ), as well as suprachiasmatic cells. We speculate that in the postnatal/adult human hypothalamus, neurogenesis occurs in a highly complex, exquisitely sophisticated neurogenic niche consisting of at least four subniches; this structure has a key role in the regulation of extrahypothalamic neurogenesis, and hypothalamic and extrahypothalamic neural circuits, partly through the release of neurotransmitters, neuropeptides, extracellular vesicles (EVs) and non-coding RNAs (ncRNAs).

Uncovering the brain-wide pattern of synaptic input to vasopressin-expressing neurons in the paraventricular nucleus of the hypothalamus

Arginine vasopressin (AVP) is a neuropeptide critical for the mammalian stress response and social behavior. AVP produced in the hypothalamus regulates water osmolality and vasoconstriction in the body, and in the brain, it regulates social behavior, aggression, and anxiety. However, the circuit mechanisms that link AVP to social behavior, homeostatic function, and disease are not well understood. This study investigates the circuit configurations of AVP-expressing neurons in the rodent hypothalamus and characterizes synaptic input from the entire brain. We targeted the paraventricular nucleus (PVN) using retrograde viral tracing techniques to identify direct afferent synaptic connections made onto AVP-expressing neurons. AVP neurons in the PVN display region-specific anatomical configurations that reflect their unique contributions to homeostatic function, motor behaviors, feeding, and affiliative behavior. The afferent connections identified were similar in both sexes and subsequent molecular investigation of these inputs shows that those local hypothalamic inputs are overwhelmingly nonpeptidergic cells indicating a potential interneuron nexus between hormone cell activation and broader cortical connection. This proposed work reveals new insights into the organization of social behavior circuits in the brain, and how neuropeptides act centrally to modulate social behaviors.

C-type natriuretic peptide (CNP) in the paraventricular nucleus-mediated renal sympatho-inhibition

Volume reflex produces sympatho-inhibition that is mediated by the hypothalamic paraventricular nucleus (PVN). However, the mechanisms for the sympatho-inhibitory role of the PVN and the neurochemical factors involved remain to be identified. In this study, we proposed C-type natriuretic peptide (CNP) as a potential mediator of this sympatho-inhibition within the PVN. Microinjection of CNP (1.0 μg) into the PVN significantly decreased renal sympathetic nerve activity (RSNA) (-25.8% ± 1.8% vs. -3.6% ± 1.5%), mean arterial pressure (-15.0 ± 1.9 vs. -0.1 ± 0.9 mmHg) and heart rate (-23.6 ± 3.5 vs. -0.3 ± 0.9 beats/min) compared with microinjection of vehicle. Picoinjection of CNP significantly decreased the basal discharge of extracellular single-unit recordings in 5/6 (83%) rostral ventrolateral medulla (RVLM)-projecting PVN neurons and in 6/13 (46%) of the neurons that were not antidromically activated from the RVLM. We also observed that natriuretic peptide receptor type C (NPR-C) was present on the RVLM projecting PVN neurons detected by dual-labeling with retrograde tracer. Prior NPR-C siRNA microinjection into the PVN significantly blunted the decrease in RSNA to CNP microinjections into the PVN. Volume expansion-mediated reduction in RSNA was significantly blunted by prior administration of NPR-C siRNA into the PVN. These results suggest a potential role for CNP within the PVN in regulating RSNA, specifically under physiological conditions of alterations in fluid balance.

Windows into stress: a glimpse at emerging roles for CRHPVN neurons

The corticotropin-releasing hormone cells in the paraventricular nucleus of the hypothalamus (CRH^PVN) control the slow endocrine response to stress. The synapses on these cells are exquisitely sensitive to acute stress, leveraging local signals to leave a lasting imprint on this system. Additionally, recent work indicates that these cells also play key roles in the control of distinct stress and survival behaviors. Here we review these observations and provide a perspective on the role of CRH^PVN neurons as integrative and malleable hubs for behavioral, physiological, and endocrine responses to stress.

Estradiol-mediated protection against high-fat diet induced anxiety and obesity is associated with changes in the gut microbiota in female mice

Decreased estrogens during menopause are associated with increased risk of anxiety, depression, type 2 diabetes and obesity. Similarly, depleting estrogens in rodents by ovariectomy, combined with a high-fat diet (HFD), increases anxiety and adiposity. How estrogens and diet interact to affect anxiety and metabolism is poorly understood. Mounting evidence indicates that gut microbiota influence anxiety and metabolism. Here, we investigated the effects of estradiol (E) and HFD on anxiety, metabolism, and their correlation with changes in gut microbiota in female mice. Adult C57BL/6J mice were ovariectomized, implanted with E or vehicle-containing capsules and fed a standard diet or HFD. Anxiety-like behavior was assessed and neuronal activation was measured by c-fos immunoreactivity throughout the brain using iDISCO. HFD increased anxiety-like behavior, while E reduced this HFD-dependent anxiogenic effect. Interestingly, E decreased neuronal activation in brain regions involved in anxiety and metabolism. E treatment also altered gut microbes, a subset of which were associated with anxiety-like behavior. These findings provide insight into gut microbiota-based therapies for anxiety and metabolic disorders associated with declining estrogens in menopausal women.

Feeding-induced hepatokines and crosstalk with multi-organ: A novel therapeutic target for Type 2 diabetes

Hyperglycemia, which can be caused by either an insulin deficit and/or insulin resistance, is the main symptom of Type 2 diabetes, a significant endocrine metabolic illness. Conventional medications, including insulin and oral antidiabetic medicines, can alleviate the signs of diabetes but cannot restore insulin release in a physiologically normal amount. The liver detects and reacts to shifts in the nutritional condition that occur under a wide variety of metabolic situations, making it an essential organ for maintaining energy homeostasis. It also performs a crucial function in glucolipid metabolism through the secretion of hepatokines. Emerging research shows that feeding induces hepatokines release, which regulates glucose and lipid metabolism. Notably, these feeding-induced hepatokines act on multiple organs to regulate glucolipotoxicity and thus influence the development of T2DM. In this review, we focus on describing how feeding-induced cross-talk between hepatokines, including Adropin, Manf, Leap2 and Pcsk9, and metabolic organs (e.g.brain, heart, pancreas, and adipose tissue) affects metabolic disorders, thus revealing a novel approach for both controlling and managing of Type 2 diabetes as a promising medication.

GABAergic leptin receptor-expressing neurons in the dorsomedial hypothalamus project to brown adipose tissue-related neurons in the paraventricular nucleus of mice

Brown adipose tissue (BAT) contributes to energy homeostasis via nonshivering thermogenesis. The BAT is densely innervated by the sympathetic nervous system (SNS) and activity of pre-autonomic neurons modulates the sympathetic outflow. Leptin, an adipocyte hormone, alters energy homeostasis and thermogenesis of BAT via several neuronal circuits; however, the cellular effects of leptin on interscapular BAT (iBAT)-related neurons in the hypothalamus remain to be determined. In this study, we used pseudorabies virus (PRV) to identify iBAT-related neurons in the paraventricular nucleus (PVN) of the hypothalamus and test the hypothesis that iBAT-related PVN neurons are modulated by leptin. Inoculation of iBAT with PRV in leptin receptor reporter mice (Lepr:EGFP) demonstrated that a population of iBAT-related PVN neurons expresses Lepr receptors. Our electrophysiological findings revealed that leptin application caused hyperpolarization in some of iBAT-related PVN neurons. Bath application of leptin also modulated excitatory and inhibitory neurotransmission to most of iBAT-related PVN neurons. Using channel rhodopsin assisted circuit mapping we found that GABAergic and glutamatergic Lepr-expressing neurons in the dorsomedial hypothalamus/dorsal hypothalamic area (dDMH/DHA) project to PVN neurons; however, connected iBAT-related PVN neurons receive exclusively inhibitory signals from Lepr-expressing dDMH/DHA neurons.

Thyroid hormone dynamics of Tharparkar and Sahiwal cattle during induced heat stress

Thyroid hormones and Cortisol level are the essential biomarkers in the assessment of stress condition. This study was done to estimate the metabolic hormonal profile of Tharparkar and Sahiwal during heat stress condition. The experiment was conducted on two groups consisting of Tharparkar and Sahiwal animals (5 in each group) and the experimental period comprised a 7-day acclimatization period, a heat exposure period of 21 days at control (25 °C), moderate (35 °C) and severe (42 °C) heat stress within a 9-10-day recovery period between each exposure. The hormonal concentrations of T₃, T₄ and cortisol were determined in serum. The serum concentration of Thyroxine (T₄) and tri-iodothyronine (T₃) decreases whereas cortisol level increases in both the breeds when subjected to heat stress. However, the serum level of T₄ was significantly (p < 0.05) more declined in Sahiwal as compared to Tharparkar but there was no significant difference found between the two breeds in serum T₃ levels. The cortisol levels were elevated in both breeds during heat stress but significantly (p < 0.05) more elevated in the Sahiwal. Hence, observations of these hormonal profiles suggest a better thermo-adaptability in Tharparkar as compared to Sahiwal.

Alterations in the activation of corticotropin-releasing factor neurons in the paraventricular nucleus following a single or multiple days of sleep restriction

Sleep disturbances are common among disorders associated with hypothalamic pituitary-adrenal (HPA) axis dysfunction, such as depression and anxiety. This comorbidity may partly be the result of the intersection between the role of the HPA axis in mediating the stress response and its involvement in sleep-wake cyclicity. Our previous work has shown that following 20 h of sleep restriction, mice show a blunting of the HPA axis in response to an acute stressor. Furthermore, these responses differ in a sex-dependent manner. This study sought to examine the effect of sleep restriction on corticotropin-releasing factor (CRF)-containing neurons in the paraventricular nucleus (PVN) of the hypothalamus. Male and female Crf-IRES-Cre: Ai14 (Tdtomato) reporter mice were sleep restricted for 20 h daily for either a single or three consecutive days using the modified multiple platform method. These mice allowed the visualization of CRF+ neurons throughout the brain. Animals were subjected to acute restraint stress, and their brains were collected to assess PVN neuronal activation via c-Fos immunohistochemistry. Analyses of cell counts revealed an ablation of the restraint-induced increase in both CRF/c-Fos colocalization and overall c-Fos expression in female mice following both a single day and three days of sleep restriction. Males showed an overall decrease in restraint-induced c-Fos levels following a single day of sleep restriction. However, male mice examined after three days of sleep restriction showed a recovery in PVN-CRF and overall PVN neuronal activation. These data suggest the sex dependent dysregulation in CRF function following sleep restriction.

Sex differences in basal reelin levels in the paraventricular hypothalamus and in response to chronic stress induced by repeated corticosterone in rats

Repeated exposure to the stress hormone corticosterone results in depressive-like behaviours paralleled by the downregulation of hippocampal reelin expression. Reelin is expressed in key neural populations involved in the stress response, but whether its hypothalamic expression is sex-specific or involved in sex-specific vulnerability to stress is unknown. Female and male rats were treated with either daily vehicle or corticosterone injections (40 mg/kg) for 21 days. Thereafter, they were subjected to several behavioural tasks before being sacrificed to allow the analysis of reelin expression in hypothalamic nuclei. The basal density of reelin-positive cells in males was significantly higher in the paraventricular nucleus (19 %) and in the medial preoptic area (51 %) compared to females. Chronic corticosterone injections increased the immobility time in the forced swim test in males (107 %) and females (108 %) and decreased the exploration of the elevated plus maze in males (34 %). Corticosterone also caused a significant decrease in the density of reelin-positive cells in males, in both ventrodorsal (37 %) and ventrolateral (32 %) subdivisions of the paraventricular nucleus, while not affecting females. Moreover, in the paraventricular nucleus of males, 30 % of the basal reelin-positive cells co-expressed oxytocin while only 17.5 % did in females, showing a positive correlation between reelin and oxytocin levels. Chronic corticosterone did not significantly affect co-localization levels. For the first time, this study shows that there is a sexually dimorphic subpopulation of reelin-positive neurons in the paraventricular nucleus that can be differentially affected by chronic stress.

Vasopressin neurons in the paraventricular hypothalamus promote wakefulness via lateral hypothalamic orexin neurons

The sleep-wakefulness cycle is regulated by complicated neural networks that include many different populations of neurons throughout the brain. Arginine vasopressin neurons in the paraventricular nucleus of the hypothalamus (PVH^AVP) regulate various physiological events and behaviors, such as body-fluid homeostasis, blood pressure, stress response, social interaction, and feeding. Changes in arousal level often accompany these PVH^AVP-mediated adaptive responses. However, the contribution of PVH^AVP neurons to sleep-wakefulness regulation has remained unknown. Here, we report the involvement of PVH^AVP neurons in arousal promotion. Optogenetic stimulation of PVH^AVP neurons rapidly induced transitions to wakefulness from both NREM and REM sleep. This arousal effect was dependent on AVP expression in these neurons. Similarly, chemogenetic activation of PVH^AVP neurons increased wakefulness and reduced NREM and REM sleep, whereas chemogenetic inhibition of these neurons significantly reduced wakefulness and increased NREM sleep. We observed dense projections of PVH^AVP neurons in the lateral hypothalamus with potential connections to orexin/hypocretin (LH^Orx) neurons. Optogenetic stimulation of PVH^AVP neuronal fibers in the LH immediately induced wakefulness, whereas blocking orexin receptors attenuated the arousal effect of PVH^AVP neuronal activation drastically. Monosynaptic rabies-virus tracing revealed that PVH^AVP neurons receive inputs from multiple brain regions involved in sleep-wakefulness regulation, as well as those involved in stress response and energy metabolism. Moreover, PVH^AVP neurons mediated the arousal induced by novelty stress and a melanocortin receptor agonist melanotan-II. Thus, our data suggested that PVH^AVP neurons promote wakefulness via LH^Orx neurons in the basal sleep-wakefulness and some stressful conditions.

Sleep dysregulation in sympathetic-mediated diseases: implications for disease progression

The autonomic nervous system (ANS) plays an important role in the coordination of several physiological functions including sleep/wake process. Significant changes in ANS activity occur during wake-to-sleep transition maintaining the adequate cardiorespiratory regulation and brain activity. Since sleep is a complex homeostatic function, partly regulated by the ANS, it is not surprising that sleep disruption trigger and/or evidence symptoms of ANS impairment. Indeed, several studies suggest a bidirectional relationship between impaired ANS function (i.e. enhanced sympathetic drive), and the emergence/development of sleep disorders. Furthermore, several epidemiological studies described a strong association between sympathetic-mediated diseases and the development and maintenance of sleep disorders resulting in a vicious cycle with adverse outcomes and increased mortality risk. However, which and how the sleep/wake control and ANS circuitry becomes affected during the progression of ANS-related diseases remains poorly understood. Thus, understanding the physiological mechanisms underpinning sleep/wake-dependent sympathetic modulation could provide insights into diseases involving autonomic dysfunction. The purpose of this review is to explore potential neural mechanisms involved in both the onset/maintenance of sympathetic-mediated diseases (Rett syndrome, congenital central hypoventilation syndrome, obstructive sleep apnoea, type 2 diabetes, obesity, heart failure, hypertension, and neurodegenerative diseases) and their plausible contribution to the generation of sleep disorders in order to review evidence that may serve to establish a causal link between sleep disorders and heightened sympathetic activity.

Hypothalamic Irak4 is a genetically controlled regulator of hypoglycemia-induced glucagon secretion

OBJECTIVES

Glucagon secretion to stimulate hepatic glucose production is the first line of defense against hypoglycemia. This response is triggered by so far incompletely characterized central hypoglycemia-sensing mechanisms, which control autonomous nervous activity and hormone secretion. The objective of this study was to identify novel hypothalamic genes controlling insulin-induced glucagon secretion.

METHODS

To obtain new information on the mechanisms of hypothalamic hypoglycemia sensing, we combined genetic and transcriptomic analysis of glucagon response to insulin-induced hypoglycemia in a panel of BXD recombinant inbred mice.

RESULTS

We identified two QTLs on chromosome 8 and chromosome 15. We further investigated the role of Irak4 and Cpne8, both located in the QTL on chromosome 15, in C57BL/6J and DBA/2J mice, the BXD mouse parental strains. We found that the poor glucagon response of DBA/2J mice was associated with higher hypothalamic expression of Irak4, which encodes a kinase acting downstream of the interleukin-1 receptor (Il-1R), and of Il-ß when compared with C57BL/6J mice. We showed that intracerebroventricular administration of an Il-1R antagonist in DBA/2J mice restored insulin-induced glucagon secretion; this was associated with increased c-fos expression in the arcuate and paraventricular nuclei of the hypothalamus and with higher activation of both branches of the autonomous nervous system. Whole body inactivation of Cpne8, which encodes a Ca++-dependent regulator of membrane trafficking and exocytosis, however, had no impact on insulin-induced glucagon secretion.

CONCLUSIONS

Collectively, our data identify Irak4 as a genetically controlled regulator of hypoglycemia-activated hypothalamic neurons and glucagon secretion.

State-dependent activity dynamics of hypothalamic stress effector neurons

The stress response necessitates an immediate boost in vital physiological functions from their homeostatic operation to an elevated emergency response. However, the neural mechanisms underlying this state-dependent change remain largely unknown. Using a combination of in vivo and ex vivo electrophysiology with computational modeling, we report that corticotropin releasing hormone (CRH) neurons in the paraventricular nucleus of the hypothalamus (PVN), the effector neurons of hormonal stress response, rapidly transition between distinct activity states through recurrent inhibition. Specifically, in vivo optrode recording shows that under non-stress conditions, CRH_PVN neurons often fire with rhythmic brief bursts (RB), which, somewhat counterintuitively, constrains firing rate due to long (~2 s) interburst intervals. Stressful stimuli rapidly switch RB to continuous single spiking (SS), permitting a large increase in firing rate. A spiking network model shows that recurrent inhibition can control this activity-state switch, and more broadly the gain of spiking responses to excitatory inputs. In biological CRH_PVN neurons ex vivo, the injection of whole-cell currents derived from our computational model recreates the in vivo-like switch between RB and SS, providing direct evidence that physiologically relevant network inputs enable state-dependent computation in single neurons. Together, we present a novel mechanism for state-dependent activity dynamics in CRH_PVN neurons.

The ins and outs of the caudal nucleus of the solitary tract: An overview of cellular populations and anatomical connections

The body and brain are in constant two-way communication. Driving this communication is a region in the lower brainstem: the dorsal vagal complex. Within the dorsal vagal complex, the caudal nucleus of the solitary tract (cNTS) is a major first stop for incoming information from the body to the brain carried by the vagus nerve. The anatomy of this region makes it ideally positioned to respond to signals of change in both emotional and bodily states. In turn, the cNTS controls the activity of regions throughout the brain that are involved in the control of both behaviour and physiology. This review is intended to help anyone with an interest in the cNTS. First, I provide an overview of the architecture of the cNTS and outline the wide range of neurotransmitters expressed in subsets of neurons in the cNTS. Next, in detail, I discuss the known inputs and outputs of the cNTS and briefly highlight what is known regarding the neurochemical makeup and function of those connections. Then, I discuss one group of cNTS neurons: glucagon-like peptide-1 (GLP-1)-expressing neurons. GLP-1 neurons serve as a good example of a group of cNTS neurons, which receive input from varied sources and have the ability to modulate both behaviour and physiology. Finally, I consider what we might learn about other cNTS neurons from our study of GLP-1 neurons and why it is important to remember that the manipulation of molecularly defined subsets of cNTS neurons is likely to affect physiology and behaviours beyond those monitored in individual experiments.

Paraventricular hypothalamic vasopressin neurons induce self-grooming in mice

Self-grooming plays an essential role in hygiene maintenance, thermoregulation, and stress response. However, the neural populations involved in self-grooming remain largely unknown. The paraventricular hypothalamic nucleus (PVH) has been implicated in the regulation of self-grooming. Arginine vasopressin-producing neurons are among the major neuronal populations in the PVH (PVH^AVP), which play important roles in water homeostasis, blood pressure regulation, feeding, and stress response. Here, we report the critical role of PVH^AVP neurons in the induction of self-grooming. Optogenetic activation of PVH^AVP neurons immediately induced self-grooming in freely moving mice. Chemogenetic activation of these neurons also increased time spent self-grooming. In contrast, their chemogenetic inhibition significantly reduced naturally occurring self-grooming, suggesting that PVH^AVP-induced grooming has physiological relevance. Notably, optogenetic activation of PVH^AVP neurons triggered self-grooming over other adaptive behaviors, such as voracious feeding induced by fasting and social interaction with female mice. Thus, our study proposes the novel role of PVH^AVP neurons in regulating self-grooming behavior and, consequently, hygiene maintenance and stress response. Furthermore, uncontrolled activation of these neurons may be potentially relevant to diseases characterized by compulsive behaviors and impaired social interaction, such as autism, obsessive–compulsive disorder, and anorexia nervosa.

Cardiorenal Syndrome: The Role of Neural Connections Between the Heart and the Kidneys

The maintenance of cardiovascular homeostasis is highly dependent on tightly controlled interactions between the heart and the kidneys. Therefore, it is not surprising that a dysfunction in one organ affects the other. This interlinking relationship is aptly demonstrated in the cardiorenal syndrome. The characteristics of the cardiorenal syndrome state include alterations in neurohumoral drive, autonomic reflexes, and fluid balance. The evidence suggests that several factors contribute to these alterations. These may include peripheral and central nervous system abnormalities. However, accumulating evidence from animals with experimental models of congestive heart failure and renal dysfunction as well as humans with the cardiorenal syndrome suggests that alterations in neural pathways, from and to the kidneys and the heart, including the central nervous system are involved in regulating sympathetic outflow and may be critically important in the alterations in neurohumoral drive, autonomic reflexes, and fluid balance commonly observed in the cardiorenal syndrome. This review focuses on studies implicating neural pathways, particularly the afferent and efferent signals from the heart and the kidneys integrating at the level of the paraventricular nucleus in the hypothalamus to alter neurohumoral drive, autonomic pathways, and fluid balance. Further, it explores the potential mechanisms of action for the known beneficial use of various medications or potential novel therapeutic manipulations for the treatment of the cardiorenal syndrome. A comprehensive understanding of these mechanisms will enhance our ability to treat cardiorenal conditions and their cardiovascular complications more efficaciously and thoroughly.

Social isolation modulates appetite and avoidance behavior via a common oxytocinergic circuit in larval zebrafish

Animal brains have evolved to encode social stimuli and transform these representations into advantageous behavioral responses. The commonalities and differences of these representations across species are not well-understood. Here, we show that social isolation activates an oxytocinergic (OXT), nociceptive circuit in the larval zebrafish hypothalamus and that chemical cues released from conspecific animals are potent modulators of this circuit's activity. We delineate an olfactory to subpallial pathway that transmits chemical social cues to OXT circuitry, where they are transformed into diverse outputs simultaneously regulating avoidance and feeding behaviors. Our data allow us to propose a model through which social stimuli are integrated within a fundamental neural circuit to mediate diverse adaptive behaviours.

Prosomeric Hypothalamic Distribution of Tyrosine Hydroxylase Positive Cells in Adolescent Rats

Most of the studies on neurochemical mapping, connectivity, and physiology in the hypothalamic region were carried out in rats and under the columnar morphologic paradigm. According to the columnar model, the entire hypothalamic region lies ventrally within the diencephalon, which includes preoptic, anterior, tuberal, and mamillary anteroposterior regions, and sometimes identifying dorsal, intermediate, and ventral hypothalamic partitions. This model is weak in providing little or no experimentally corroborated causal explanation of such subdivisions. In contrast, the modern prosomeric model uses different axial assumptions based on the parallel courses of the brain floor, alar-basal boundary, and brain roof (all causally explained). This model also postulates that the hypothalamus and telencephalon jointly form the secondary prosencephalon, separately from and rostral to the diencephalon proper. The hypothalamus is divided into two neuromeric (transverse) parts called peduncular and terminal hypothalamus (PHy and THy). The classic anteroposterior (AP) divisions of the columnar hypothalamus are rather seen as dorsoventral subdivisions of the hypothalamic alar and basal plates. In this study, we offered a prosomeric immunohistochemical mapping in the rat of hypothalamic cells expressing tyrosine hydroxylase (TH), which is the enzyme that catalyzes the conversion of L-tyrosine to levodopa (L-DOPA) and a precursor of dopamine. This mapping was also combined with markers for diverse hypothalamic nuclei [agouti-related peptide (Agrp), arginine vasopressin (Avp), cocaine and amphetamine-regulated transcript (Cart), corticotropin releasing Hormone (Crh), melanin concentrating hormone (Mch), neuropeptide Y (Npy), oxytocin/neurophysin I (Oxt), proopiomelanocortin (Pomc), somatostatin (Sst), tyrosine hidroxilase (Th), and thyrotropin releasing hormone (Trh)]. TH-positive cells are particularly abundant within the periventricular stratum of the paraventricular and subparaventricular alar domains. In the tuberal region, most labeled cells are found in the acroterminal arcuate nucleus and in the terminal periventricular stratum. The dorsal retrotuberal region (PHy) contains the A13 cell group of TH-positive cells. In addition, some TH cells appear in the perimamillary and retromamillary regions. The prosomeric model proved useful for determining the precise location of TH-positive cells relative to possible origins of morphogenetic signals, thus aiding potential causal explanation of position-related specification of this hypothalamic cell type.

The Paraventricular Nucleus of the Hypothalamus in Control of Blood Pressure and Blood Pressure Variability

The paraventricular nucleus (PVN) is a highly organized structure of the hypothalamus that has a key role in regulating cardiovascular and osmotic homeostasis. Functionally, the PVN is divided into autonomic and neuroendocrine (neurosecretory) compartments, both equally important for maintaining blood pressure (BP) and body fluids in the physiological range. Neurosecretory magnocellular neurons (MCNs) of the PVN are the main source of the hormones vasopressin (VP), responsible for water conservation and hydromineral balance, and oxytocin (OT), involved in parturition and milk ejection during lactation. Further, neurosecretory parvocellular neurons (PCNs) take part in modulation of the hypothalamic–pituitary–adrenal axis and stress responses. Additionally, the PVN takes central place in autonomic adjustment of BP to environmental challenges and contributes to its variability (BPV), underpinning the PVN as an autonomic master controller of cardiovascular function. Autonomic PCNs of the PVN modulate sympathetic outflow toward heart, blood vessels and kidneys. These pre-autonomic neurons send projections to the vasomotor nucleus of rostral ventrolateral medulla and to intermediolateral column of the spinal cord, where postganglionic fibers toward target organs arise. Also, PVN PCNs synapse with NTS neurons which are the end-point of baroreceptor primary afferents, thus, enabling the PVN to modify the function of baroreflex. Neuroendocrine and autonomic parts of the PVN are segregated morphologically but they work in concert when the organism is exposed to environmental challenges via somatodendritically released VP and OT by MCNs. The purpose of this overview is to address both neuroendocrine and autonomic PVN roles in BP and BPV regulation.

Disruption of CRTC1 and CRTC2 in Sim1 cells strongly increases high-fat diet intake in female mice but has a modest impact on male mice

cAMP responsive element binding protein (CREB)-regulated transcription coactivators (CRTCs) regulate gene transcription in response to an increase in intracellular cAMP or Ca²⁺ levels. To date, three isoforms of CRTC have been identified in mammals. All CRTCs are widely expressed in various regions of the brain. Numerous studies have shown the importance of CREB and CRTC in energy homeostasis. In the brain, the paraventricular nucleus of the hypothalamus (PVH) plays a critical role in energy metabolism, and CRTC1 and CRTC2 are highly expressed in PVH neuronal cells. The single-minded homolog 1 gene (Sim1) is densely expressed in PVH neurons and in some areas of the amygdala neurons. To determine the role of CRTCs in PVH on energy metabolism, we generated mice that lacked CRTC1 and CRTC2 in Sim1 cells using Sim-1 cre mice. We found that Sim1 cell-specific CRTC1 and CRTC2 double-knockout mice were sensitive to high-fat diet (HFD)-induced obesity. Sim1 cell-specific CRTC1 and CRTC2 double knockout mice showed hyperphagia specifically for the HFD, but not for the normal chow diet, increased fat mass, and no change in energy expenditure. Interestingly, these phenotypes were stronger in female mice than in male mice, and a weak phenotype was observed in the normal chow diet. The lack of CRTC1 and CRTC2 in Sim1 cells changed the mRNA levels of some neuropeptides that regulate energy metabolism in female mice fed an HFD. Taken together, our findings suggest that CRTCs in Sim1 cells regulate gene expression and suppress excessive fat intake, especially in female mice.