Modulation of SF1 Neuron Activity Coordinately Regulates Both Feeding Behavior and Associated Emotional States

CPT1C deficiency in SF1 neurons impairs early metabolic adaptation to dietary fats, leading to obesity

OBJECTIVES

SF1 neurons of the ventromedial hypothalamus (VMH) play a pivotal role in regulating body weight and adiposity, particularly in response to a high-fat diet (HFD), as well as in the recovery from insulin-induced hypoglycemia. While the brain-specific CPT1C isoform is well known for its role in controlling food intake and energy homeostasis, its function within specific hypothalamic neuronal populations remains largely unexplored. Here, we explore the role of CPT1C in SF1 neurons.

METHODS

Mice deficient in CPT1C within SF1 neurons were generated, and their response to a HFD was investigated.

RESULTS

SF1-Cpt1c-KO mice fail to adjust their caloric intake during initial HFD exposure, which is associated with impaired activation of the melanocortin system. Furthermore, these mice exhibit disrupted metabolic gene expression in the liver, muscle, and adipose tissue, leading to increased adiposity independently of food intake. In contrast, their response to glucose or insulin challenges remains intact. After long-term HFD exposure, SF1-Cpt1c-KO mice are more prone to developing obesity and glucose intolerance than control littermates, with males exhibiting a more severe phenotype. Interestingly, CPT1C deficiency in SF1 neurons also results in elevated hypothalamic endocannabinoid (eCB) levels under both chow and HFD conditions. We propose that this sustained eCB elevation reduces VMH activation by fatty acids and impairs the SF1-POMC drive upon fat intake.

CONCLUSION

Our findings establish CPT1C in SF1 neurons as essential for VMH-driven dietary fat sensing, satiety, and lipid metabolic adaptation.

International Union of Basic and Clinical Pharmacology. CXIX. Fundamental insights and clinical relevance regarding the carnitine palmitoyltransferase family of enzymes

The carnitine palmitoyltransferases (CPTs) play a key role in controlling the oxidation of long-chain fatty acids and are potential therapeutic targets for diseases with a strong metabolic component, such as obesity, diabetes, and cancer. Four distinct proteins are CPT1A, CPT1B, CPT1C, and CPT2, differing in tissue expression and catalytic activity. CPT1s are finely regulated by malonyl-CoA, a metabolite whose intracellular levels reflect the cell's nutritional state. Although CPT1C does not exhibit significant catalytic activity, it is capable of modulating the functioning of other neuronal proteins. Structurally, all CPTs share a Y-shaped catalytic tunnel that allows the entry of 2 substrates and accommodation of the acyl group in a hydrophobic pocket. Several molecules targeting these enzymes have been described, some showing potential in normalizing blood glucose levels in diabetic patients, and others that, through a central mechanism, are anorexigenic and enhance energy expenditure. However, given the critical roles that CPTs play in certain tissues, such as the heart, liver, and brain, it is essential to fully understand the differences between the various isoforms. We analyze in detail the structure of these proteins, their cellular and physiological functions, and their potential as therapeutic targets in diseases such as obesity, diabetes, and cancer. We also describe drugs identified to date as having inhibitory or activating capabilities for these proteins. This knowledge will support the design of new drugs specific to each isoform, and the development of nanomedicines that can selectively target particular tissues or cells. SIGNIFICANCE STATEMENT: Carnitine palmitoyltransferase (CPT) proteins, as gatekeepers of fatty acid oxidation, have great potential as pharmacological targets to treat metabolic diseases like obesity, diabetes, and cancer. In recent years, significant progress has been made in understanding the 3-dimensional structure of CPTs and their pathophysiological functions. A deeper understanding of the differences between the various CPT family members will enable the design of selective drugs and therapeutic approaches with fewer side effects.

TGR5 receptors in SF1-expressing neurons of the ventromedial hypothalamus regulate glucose homeostasis

OBJECTIVE

Steroidogenic factor-1 (SF1) neurons of the ventromedial hypothalamus play key roles in the regulation of food intake, body weight and glucose metabolism. The bile acid receptor Takeda G protein-coupled receptor 5 (TGR5) is expressed in the hypothalamus, where it determines some of the actions of bile acids on food intake and body weight through still poorly defined neuronal mechanisms. Here, we examined the role of TGR5 in SF1 neurons in the regulation of energy balance and glucose metabolism.

METHODS

We used a genetic approach combined with metabolic phenotyping and molecular analyses to establish the effect of TGR5 deletion in SF1 neurons on meal pattern, body weight, body composition, energy expenditure and use of energy substrates as well as on possible changes in glucose handling and insulin sensitivity.

RESULTS

Our findings reveal that TGR5 in SF1 neurons does not play a major role in the regulation of food intake or body weight under standard chow, but it is involved in the adaptive feeding response to the acute exposure to cold or to a hypercaloric, high-fat diet, without changes in energy expenditure. Notably, TGR5 in SF1 neurons hinder glucose metabolism, since deletion of the receptor improves whole-body glucose uptake through heightened insulin signaling in the hypothalamus and in the brown adipose tissue.

CONCLUSIONS

TGR5 in SF1 neurons favours satiety by differently modifying the meal pattern in response to specific metabolic cues. These studies also reveal a novel key function for TGR5 in SF1 neurons in the regulation of whole-body insulin sensitivity, providing new insight into the role played by neuronal TGR5 in the regulation of metabolism.

How can ethology inform the neuroscience of fear, aggression and dominance?

The study of behaviour is dominated by two approaches. On the one hand, ethologists aim to understand how behaviour promotes adaptation to natural contexts. On the other, neuroscientists aim to understand the molecular, cellular, circuit and psychological origins of behaviour. These two complementary approaches must be combined to arrive at a full understanding of behaviour in its natural setting. However, methodological limitations have restricted most neuroscientific research to the study of how discrete sensory stimuli elicit simple behavioural responses under controlled laboratory conditions that are only distantly related to those encountered in real life. Fortunately, the recent advent of neural monitoring and manipulation tools adapted for use in freely behaving animals has enabled neuroscientists to incorporate naturalistic behaviours into their studies and to begin to consider ethological questions. Here, we examine the promises and pitfalls of this trend by describing how investigations of rodent fear, aggression and dominance behaviours are changing to take advantage of an ethological appreciation of behaviour. We lay out current impediments to this approach and propose a framework for the evolution of the field that will allow us to take maximal advantage of an ethological approach to neuroscience and to increase its relevance for understanding human behaviour.

Population-Based Study of Rare Coding Variants in NR5A1/SF-1

Background

Steroidogenic Factor 1/Nuclear Receptor Subfamily 5 Group A Member 1 (SF-1/NR5A1) is critical for the development and function of sex organs, influencing steroidogenesis and reproduction. While rare deleterious NR5A1/SF-1 variants have been identified in individuals with various differences of sex development (DSD), primary ovarian insufficiency, and infertility, their impact on the general population remains unclear.

Methods

We analyzed health records and exome sequencing data from up to 420 162 individuals (227 858 women) from the UK Biobank study to assess the impact of rare (frequency < 0.1%) predicted deleterious NR5A1/SF-1 variants on age at menopause and 26 other traits.

Results

No carriers of rare protein truncating variants in NR5A1/SF-1 were identified. We found that the previously reported association of rare deleterious missense NR5A1/SF-1 variants with earlier age at menopause is driven by variants in the DNA binding domain (DBD) and ligand binding domain (LBD) (combined test: beta = -2.36 years/allele, [95% CI: 3.21, -1.51], N = 107 carriers, P = 4.6 × 10-8). Carriers also had a higher risk of adult obesity (OR = 1.061, [95% CI: 1.003, 1.104], N = 344, P = .015), particularly among women (OR = 1.095 [95% CI: 1.034, 1.163, P = 3.87 × 10-3], N = 176), but not men (OR = 1.019, [95% CI: 0.955, 1.088], P = .57, N = 168).

Conclusion

Deleterious missense variants in the DBD and LBD likely disrupt NR5A1/SF-1 function. This study broadens the relevance of deleterious NR5A1/SF-1 variants beyond rare DSDs, suggesting the need for extended phenotyping and monitoring of affected individuals.

Auditory pallial regulation of the social behavior network

Sensory cues such as vocalizations contain important social information. Processing social features of vocalizations (e.g., vocalizer identity, emotional state) necessitates unpacking the complex sound streams in song or speech; this depends on circuits in pallial cortex. But whether and how this information is then transferred to limbic and hypothalamic regions remains a mystery. Here, using gregarious, vocal songbirds (female Zebra finches), we identify a prominent influence of the auditory pallium on one specific node of the Social Behavior Network, the lateral ventromedial nucleus of the hypothalamus (VMHl). Electrophysiological recordings revealed that social and non-social auditory stimuli elicited stimulus-specific spike trains that permitted stimulus differentiation in a large majority of VMHl single units, while transient disruption of auditory pallium elevated immediate early gene activity in VMHl. Descending functional connections such as these may be critical for the range of vertebrate species that rely on nuanced communication signals to guide social decision-making.

Spatial transcriptomics reveals modulation of transcriptional networks across brain regions after auditory threat conditioning

Prior research has demonstrated genome-wide transcriptional changes related to fear and anxiety across species, often focusing on individual brain regions or cell types. However, the extent of gene expression differences across brain regions and how these changes interact at the level of transcriptional connectivity remains unclear. To address this, we performed spatial transcriptomics RNAseq analyses in an auditory threat conditioning paradigm in mice. We generated a spatial transcriptomic atlas of a coronal mouse brain section covering cortical and subcortical regions, corresponding to histologically defined regions. Our finding revealed widespread transcriptional responses across all brain regions examined, particularly in the medial and lateral habenula, and the choroid plexus. Network analyses highlighted altered transcriptional connectivity between cortical and subcortical regions, emphasizing the role of steroidogenic factor 1. These results provide new insights into the transcriptional networks involved in auditory threat conditioning, enhancing our understanding of molecular and neural mechanisms underlying fear and anxiety disorders.

Functional diversity along the anteroposterior axis of the ventromedial hypothalamus

Innate behaviors ensure animal survival and reproductive success. Defending their territory, escaping from predators or mating with a sexual partner, are fundamental behaviors determining the ecological fitness of individuals. Remarkably, all these behaviors share a common neural substrate, as they are under the control of the ventromedial hypothalamus (VMH). Decades of research have contributed to understanding the exquisite diversity of functional ensembles underlying the wide array of functions that the VMH carries out. These functional ensembles are usually distributed throughout the dorsoventral and mediolateral axes of this nucleus. However, increasing evidence is bringing to attention the functional diversity of the VMH across its anteroposterior axis. In this review, we will overview our current understanding of how different ensembles within the VMH control a wide array of animal behaviors, emphasizing the newly discovered roles for its anterior subdivision in the context of conspecific self-defense.

Chemogenetic Excitation of Ventromedial Hypothalamic Steroidogenic Factor 1 (SF1) Neurons Increases Muscle Thermogenesis in Mice

Allostatic adaptations to a perceived threat are crucial for survival and may tap into mechanisms serving the homeostatic control of energy balance. We previously established that exposure to predator odor (PO) in rats significantly increases skeletal muscle thermogenesis and energy expenditure (EE). Evidence highlights steroidogenic factor 1 (SF1) cells within the central and dorsomedial ventromedial hypothalamus (c/dmVMH) as a modulator of both energy homeostasis and defensive behavior. However, the brain mechanism driving elevated EE and muscle thermogenesis during PO exposure has yet to be elucidated. To assess the ability of SF1 neurons of the c/dmVMH to induce muscle thermogenesis, we used the combined technology of chemogenetics, transgenic mice, temperature transponders, and indirect calorimetry. Here, we evaluate EE and muscle thermogenesis in SF1-Cre mice exposed to PO (ferret odor) compared to transgenic and viral controls. We detected significant increases in muscle temperature, EE, and oxygen consumption following the chemogenetic stimulation of SF1 cells. However, there were no detectable changes in muscle temperature in response to PO in either the presence or absence of chemogenetic stimulation. While the specific role of the VMH SF1 cells in PO-induced thermogenesis remains uncertain, these data establish a supporting role for SF1 neurons in the induction of muscle thermogenesis and EE similar to what is seen after predator threats.

The Role of BDNF and TrkB in the Central Control of Energy and Glucose Balance: An Update

The global rise in obesity and related health issues, such as type 2 diabetes and cardiovascular disease, is alarming. Gaining a deeper insight into the central neural pathways and mechanisms that regulate energy and glucose homeostasis is crucial for developing effective interventions to combat this debilitating condition. A significant body of evidence from studies in humans and rodents indicates that brain-derived neurotrophic factor (BDNF) signaling plays a key role in regulating feeding, energy expenditure, and glycemic control. BDNF is a highly conserved neurotrophin that signals via the tropomyosin-related kinase B (TrkB) receptor to facilitate neuronal survival, differentiation, and synaptic plasticity and function. Recent studies have shed light on the mechanisms through which BDNF influences energy and glucose balance. This review will cover our current understanding of the brain regions, neural circuits, and cellular and molecular mechanisms underlying the metabolic actions of BDNF and TrkB.

Secretin-dependent signals in the ventromedial hypothalamus regulate energy metabolism and bone homeostasis in mice

Secretin, though originally discovered as a gut-derived hormone, is recently found to be abundantly expressed in the ventromedial hypothalamus, from which the central neural system controls satiety, energy metabolism, and bone homeostasis. However, the functional significance of secretin in the ventromedial hypothalamus remains unclear. Here we show that the loss of ventromedial hypothalamus-derived secretin leads to osteopenia in male and female mice, which is primarily induced by diminished cAMP response element-binding protein phosphorylation and upregulation in peripheral sympathetic activity. Moreover, the ventromedial hypothalamus-secretin inhibition also contributes to hyperphagia, dysregulated lipogenesis, and impaired thermogenesis, resulting in obesity in male and female mice. Conversely, overexpression of secretin in the ventromedial hypothalamus promotes bone mass accrual in mice of both sexes. Collectively, our findings identify an unappreciated secretin signaling in the central neural system for the regulation of energy and bone metabolism, which may serve as a new target for the clinical management of obesity and osteoporosis.

Synaptic plasticity and the role of astrocytes in central metabolic circuits

Neural circuits in the brain, primarily in the hypothalamus, are paramount to the homeostatic control of feeding and energy utilization. They integrate hunger, satiety, and body adiposity cues from the periphery and mediate the appropriate behavioral and physiological responses to satisfy the energy demands of the animal. Notably, perturbations in central homeostatic circuits have been linked to the etiology of excessive feeding and obesity. Considering the ever-changing energy requirements of the animal and required adaptations, it is not surprising that brain-feeding circuits remain plastic in adulthood and are subject to changes in synaptic strength as a consequence of nutritional status. Indeed, synapse density, probability of presynaptic transmitter release, and postsynaptic responses in hypothalamic energy balance centers are tailored to behavioral and physiological responses required to sustain survival. Mounting evidence supports key roles of astrocytes facilitating some of this plasticity. Here we discuss these synaptic plasticity mechanisms and the emerging roles of astrocytes influencing energy and glucose balance control in health and disease. This article is categorized under: Cancer > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology.

Central Channelopathies in Obesity

As obesity has raised heightening awareness, researchers have attempted to identify potential targets that can be treated for therapeutic intervention. Focusing on the central nervous system (CNS), the key organ in maintaining energy balance, a plethora of ion channels that are expressed in the CNS have been inspected and determined through manipulation in different hypothalamic neural subpopulations for their roles in fine-tuning neuronal activity on energy state alterations, possibly acting as metabolic sensors. However, a remaining gap persists between human clinical investigations and mouse studies. Despite having delineated the pathways and mechanisms of how the mouse study-identified ion channels modulate energy homeostasis, only a few targets overlap with the obesity-related risk genes extracted from human genome-wide association studies. Here, we present the most recently discovered CNS-specific metabolism-correlated ion channels using reverse and forward genetics approaches in mice and humans, respectively, in the hope of illuminating the prospects for future therapeutic development.

Ventromedial hypothalamus relays chronic stress inputs and exerts bidirectional regulation on anxiety state and related sympathetic activity

Chronic stress can induce negative emotion states, including anxiety and depression, leading to sympathetic overactivation and disturbed physiological homeostasis in peripheral tissues. While anxiety-related neural circuitry integrates chronic stress information and modulates sympathetic nervous system (SNS) activity, the critical nodes linking anxiety and sympathetic activity still need to be clarified. In our previous study, we demonstrated that the ventromedial hypothalamus (VMH) is involved in integrating chronic stress inputs and exerting influence on sympathetic activity. However, the underlying synaptic and electrophysiological mechanisms remain elusive. In this study, we combined in vitro electrophysiological recordings, behavioral tests, optogenetic manipulations, and SNS activity analyses to explore the role of VMH in linking anxiety emotion and peripheral SNS activity. Results showed that the VMH played an important role in bidirectionally regulating anxiety-like behavior and peripheral sympathetic excitation. Chronic stress enhanced excitatory inputs into VMH neurons by strengthening the connection with the paraventricular hypothalamus (PVN), hence promoting anxiety and sympathetic tone outflow, an important factor contributing to the development of metabolic imbalance in peripheral tissues and cardiovascular diseases.

Anoctamin 4 channel currents activate glucose-inhibited neurons in the mouse ventromedial hypothalamus during hypoglycemia

Glucose is the basic fuel essential for maintenance of viability and functionality of all cells. However, some neurons - namely, glucose-inhibited (GI) neurons - paradoxically increase their firing activity in low-glucose conditions and decrease that activity in high-glucose conditions. The ionic mechanisms mediating electric responses of GI neurons to glucose fluctuations remain unclear. Here, we showed that currents mediated by the anoctamin 4 (Ano4) channel are only detected in GI neurons in the ventromedial hypothalamic nucleus (VMH) and are functionally required for their activation in response to low glucose. Genetic disruption of the Ano4 gene in VMH neurons reduced blood glucose and impaired counterregulatory responses during hypoglycemia in mice. Activation of VMHAno4 neurons increased food intake and blood glucose, while chronic inhibition of VMHAno4 neurons ameliorated hyperglycemia in a type 1 diabetic mouse model. Finally, we showed that VMHAno4 neurons represent a unique orexigenic VMH population and transmit a positive valence, while stimulation of neurons that do not express Ano4 in the VMH (VMHnon-Ano4) suppress feeding and transmit a negative valence. Together, our results indicate that the Ano4 channel and VMHAno4 neurons are potential therapeutic targets for human diseases with abnormal feeding behavior or glucose imbalance.

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).

Neurochemical Basis of Inter-Organ Crosstalk in Health and Obesity: Focus on the Hypothalamus and the Brainstem

Precise neural regulation is required for maintenance of energy homeostasis. Essential to this are the hypothalamic and brainstem nuclei which are located adjacent and supra-adjacent to the circumventricular organs. They comprise multiple distinct neuronal populations which receive inputs not only from other brain regions, but also from circulating signals such as hormones, nutrients, metabolites and postprandial signals. Hence, they are ideally placed to exert a multi-tier control over metabolism. The neuronal sub-populations present in these key metabolically relevant nuclei regulate various facets of energy balance which includes appetite/satiety control, substrate utilization by peripheral organs and glucose homeostasis. In situations of heightened energy demand or excess, they maintain energy homeostasis by restoring the balance between energy intake and expenditure. While research on the metabolic role of the central nervous system has progressed rapidly, the neural circuitry and molecular mechanisms involved in regulating distinct metabolic functions have only gained traction in the last few decades. The focus of this review is to provide an updated summary of the mechanisms by which the various neuronal subpopulations, mainly located in the hypothalamus and the brainstem, regulate key metabolic functions.

Neuroanatomical characterization of the Nmu-Cre knock-in mice reveals an interconnected network of unique neuropeptidergic cells

Neuromedin U (NMU) is an evolutionary conserved neuropeptide that has been implicated in multiple processes, such as circadian regulation, energy homeostasis, reward processing and stress coping. Although the central expression of NMU has been addressed previously, the lack of specific and sensitive tools has prevented a comprehensive characterization of NMU-expressing neurons in the brain. We have generated a knock-in mouse model constitutively expressing Cre recombinase under the Nmu promoter. We have validated the model using a multi-level approach based on quantitative reverse-transcription polymerase chain reactions, in situ hybridization, a reporter mouse line and an adenoviral vector driving Cre-dependent expression of a fluorescent protein. Using the Nmu-Cre mouse, we performed a complete characterization of NMU expression in adult mouse brain, unveiling a potential midline NMU modulatory circuit with the ventromedial hypothalamic nucleus (VMH) as a key node. Moreover, immunohistochemical analysis suggested that NMU neurons in the VMH mainly constitute a unique population of hypothalamic cells. Taken together, our results suggest that Cre expression in the Nmu-Cre mouse model largely reflects NMU expression in the adult mouse brain, without altering endogenous NMU expression. Thus, the Nmu-Cre mouse model is a powerful and sensitive tool to explore the role of NMU neurons in mice.

CaMKIIa Neurons of the Ventromedial Hypothalamus Mediate Wakefulness and Anxiety-like Behavior

Insomnia and anxiety are two common and closely related clinical problems that pose a threat to individuals' physical and mental well-being. There is a possibility that some nuclei and neural circuits in the brain are shared by both insomnia and anxiety. In the present study, using a combination of chemogenetics, optogenetics, polysomnographic recordings and the classic tests of anxiety-like behaviors, we verified that the calmodulin-dependent protein kinase II alpha (CaMKIIa) neurons of the ventromedial hypothalamus (VMH) are involved in the regulation of both wakefulness and anxiety. Chemogenetic manipulation of the VMH CaMKIIa neurons elicited an apparent increase in wakefulness during activation, whereas inhibition decreased wakefulness mildly. It substantiated that the VMH CaMKIIa neurons contribute to wakefulness. Then in millisecond-scale control of neuronal activity, short-term and long-term optogenetic activation induced the initiation and maintenance of wakefulness, respectively. We also observed that mice reduced exploratory behaviors in classic anxiety tests while activating the VMH CaMKIIa neurons and were anxiolytic while inhibiting. Additionally, photostimulation of the VMH CaMKIIa axons in the paraventricular hypothalamus (PVH) mediated wakefulness and triggered anxiety-like behaviors as well. In conclusion, our results demonstrate that the VMH participates in the control of wakefulness and anxiety, and offer a neurological explanation for insomnia and anxiety, which may be valuable for therapeutic interventions such as medication and transcranial magnetic stimulation.

Increased sympathetic outflow induced by emotional stress aggravates myocardial ischemia-reperfusion injury via activation of TLR7/MyD88/IRF5 signaling pathway

BACKGROUND AND OBJECTIVE

Emotional stress substantially increases the risk of ischemic cardiovascular diseases. Previous study indicates that sympathetic outflow is increased under emotional stress. We aim to investigate the role of increased sympathetic outflow induced by emotional stress in myocardial ischemia-reperfusion (I/R) injury, and explore the underlying mechanisms.

METHODS AND RESULTS

We used Designer Receptors Exclusively Activated by Designer Drugs technique to activate the ventromedial hypothalamus (VMH), a critical emotion-related nucleus. The results revealed that emotional stress stimulated by VMH activation increased sympathetic outflow, enhanced blood pressure, aggravated myocardial I/R injury, and exacerbated infarct size. The RNA-seq and molecular detection demonstrated that toll-like receptor 7 (TLR7), myeloid differentiation factor 88 (MyD88), interferon regulatory factor 5 (IRF5), and downstream inflammatory markers in cardiomyocytes were significantly upregulated. Emotional stress-induced sympathetic outflow further exacerbated the disorder of the TLR7/MyD88/IRF5 inflammatory signaling pathway. While inhibition of the signaling pathway partially alleviated myocardial I/R injury aggravated by emotional stress-induced sympathetic outflow.

CONCLUSION

Increased sympathetic outflow induced by emotional stress activates TLR7/MyD88/IRF5 signaling pathway, ultimately aggravating I/R injury.

Top-down, auditory pallial regulation of the social behavior network

Social encounters rely on sensory cues that carry nuanced information to guide social decision-making. While high-level features of social signals are processed in the telencephalic pallium, nuclei controlling social behaviors, called the social behavior network (SBN), reside mainly in the diencephalon. Although it is well known how mammalian olfactory pallium interfaces with the SBN, there is little information for how pallial processing of other sensory modalities can modulate SBN circuits. This is surprising given the importance of complex vocalizations, for example, for social behavior in many vertebrate taxa such as humans and birds. Using gregarious and highly vocal songbirds, female Zebra finches, we asked to what extent auditory pallial circuits provide consequential input to the SBN as it processes social sensory cues. We transiently inactivated auditory pallium of female Zebra finches during song playback and examined song-induced activation in SBN nuclei. Auditory pallial inactivation impaired responses to song specifically within the lateral ventromedial nucleus of the hypothalamus (VMHl), providing the first evidence in vertebrates of a connection between auditory pallium and the SBN. This same treatment elevated feeding behavior, which also correlated with VMHl activation. This suggests that signals from auditory pallium to VMHl can tune the balance between social attention and feeding drive. A descending influence of sensory pallium on hypothalamic circuits could therefore provide a functional connection for the integration of social stimuli with internal state to influence social decision-making.

Significance

Sensory cues such as vocalizations contain important social information. These social signals can be substantially nuanced, containing information about vocalizer identity, prior experience, valence, and emotional state. Processing these features of vocalizations necessitates processing the fast, complex sound streams in song or speech, which depends on circuits in pallial cortex. But whether and how this information is then transferred to social circuits in limbic and hypothalamic regions remains a mystery. Here, we identify a top-down influence of the songbird auditory pallium on one specific node of the social behavior network within the hypothalamus. Descending functional connections such as these may be critical for the wide range of vertebrate species that rely on intricate sensory communication signals to guide social decision-making.

Arginine-vasopressin-expressing neurons in the murine suprachiasmatic nucleus exhibit a circadian rhythm in network coherence in vivo

The suprachiasmatic nucleus (SCN) is composed of functionally distinct subpopulations of GABAergic neurons which form a neural network responsible for synchronizing most physiological and behavioral circadian rhythms in mammals. To date, little is known regarding which aspects of SCN rhythmicity are generated by individual SCN neurons, and which aspects result from neuronal interaction within a network. Here, we utilize in vivo miniaturized microscopy to measure fluorescent GCaMP-reported calcium dynamics in arginine vasopressin (AVP)-expressing neurons in the intact SCN of awake, behaving mice. We report that SCN AVP neurons exhibit periodic, slow calcium waves which we demonstrate, using in vivo electrical recordings, likely reflect burst firing. Further, we observe substantial heterogeneity of function in that AVP neurons exhibit unstable rhythms, and relatively weak rhythmicity at the population level. Network analysis reveals that correlated cellular behavior, or coherence, among neuron pairs also exhibited stochastic rhythms with about 33% of pairs rhythmic at any time. Unlike single-cell variables, coherence exhibited a strong rhythm at the population level with time of maximal coherence among AVP neuronal pairs at CT/ZT 6 and 9, coinciding with the timing of maximal neuronal activity for the SCN as a whole. These results demonstrate robust circadian variation in the coordination between stochastically rhythmic neurons and that interactions between AVP neurons in the SCN may be more influential than single-cell activity in the regulation of circadian rhythms. Furthermore, they demonstrate that cells in this circuit, like those in many other circuits, exhibit profound heterogenicity of function over time and space.

Relaxin/insulin-like family peptide receptor 4 (Rxfp4) expressing hypothalamic neurons modulate food intake and preference in mice

OBJECTIVE

Insulin-like peptide 5 (INSL5) signalling, through its cognate receptor relaxin/insulin-like family peptide receptor 4 (RXFP4), has been reported to be orexigenic, and the high fat diet (HFD) preference observed in wildtype mice is altered in Rxfp4 knock-out mice. In this study, we used a new Rxfp4-Cre mouse model to investigate the mechanisms underlying these observations.

METHODS

We generated transgenic Rxfp4-Cre mice and investigated central expression of Rxfp4 by RT-qPCR, RNAscope and intraparenchymal infusion of INSL5. Rxfp4-expressing cells were chemogenetically manipulated in global Cre-reporter mice using designer receptors exclusively activated by designer drugs (DREADDs) or after stereotactic injection of a Cre-dependent AAV-DIO-Dq-DREADD targeting a population located in the ventromedial hypothalamus (RXFP4VMH). Food intake and feeding motivation were assessed in the presence and absence of a DREADD agonist. Rxfp4-expressing cells in the hypothalamus were characterised by single-cell RNA-sequencing (scRNAseq) and the connectivity of RXFP4VMH cells was investigated using viral tracing.

RESULTS

Rxfp4-Cre mice displayed Cre-reporter expression in the hypothalamus. Active expression of Rxfp4 in the adult mouse brain was confirmed by RT-qPCR and RNAscope. Functional receptor expression was supported by cyclic AMP-responses to INSL5 application in ex vivo brain slices and increased HFD and highly palatable liquid meal (HPM), but not chow, intake after intra-VMH INSL5 infusion. scRNAseq of hypothalamic RXFP4 neurons defined a cluster expressing VMH markers, alongside known appetite-modulating neuropeptide receptors (Mc4r, Cckar and Nmur2). Viral tracing demonstrated RXFP4VMH neural projections to nuclei implicated in hedonic feeding behaviour. Whole body chemogenetic inhibition (Di-DREADD) of Rxfp4-expressing cells, mimicking physiological INSL5-RXFP4 Gi-signalling, increased intake of the HFD and HPM, but not chow, whilst activation (Dq-DREADD), either at whole body level or specifically within the VMH, reduced HFD and HPM intake and motivation to work for the HPM.

CONCLUSION

These findings identify RXFP4VMH neurons as regulators of food intake and preference, and hypothalamic RXFP4 signalling as a target for feeding behaviour manipulation.

GLUT2 expression by glial fibrillary acidic protein-positive tanycytes is required for promoting feeding-response to fasting

Feeding behavior is a complex process that depends on the ability of the brain to integrate hormonal and nutritional signals, such as glucose. One glucosensing mechanism relies on the glucose transporter 2 (GLUT2) in the hypothalamus, especially in radial glia-like cells called tanycytes. Here, we analyzed whether a GLUT2-dependent glucosensing mechanism is required for the normal regulation of feeding behavior in GFAP-positive tanycytes. Genetic inactivation of Glut2 in GFAP-expressing tanycytes was performed using Cre/Lox technology. The efficiency of GFAP-tanycyte targeting was analyzed in the anteroposterior and dorsoventral axes by evaluating GFP fluorescence. Feeding behavior, hormonal levels, neuronal activity using c-Fos, and neuropeptide expression were also analyzed in the fasting-to-refeeding transition. In basal conditions, Glut2-inactivated mice had normal food intake and meal patterns. Implementation of a preceeding fasting period led to decreased total food intake and a delay in meal initiation during refeeding. Additionally, Glut2 inactivation increased the number of c-Fos-positive cells in the ventromedial nucleus in response to fasting and a deregulation of Pomc expression in the fasting-to-refeeding transition. Thus, a GLUT2-dependent glucose-sensing mechanism in GFAP-tanycytes is required to control food consumption and promote meal initiation after a fasting period.

Oxytocin signaling in the posterior hypothalamus prevents hyperphagic obesity in mice

Decades of studies have revealed molecular and neural circuit bases for body weight homeostasis. Neural hormone oxytocin (Oxt) has received attention in this context because it is produced by neurons in the paraventricular hypothalamic nucleus (PVH), a known output center of hypothalamic regulation of appetite. Oxt has an anorexigenic effect, as shown in human studies, and can mediate satiety signals in rodents. However, the function of Oxt signaling in the physiological regulation of appetite has remained in question, because whole-body knockout (KO) of Oxt or Oxt receptor (Oxtr) has little effect on food intake. We herein show that acute conditional KO (cKO) of Oxt selectively in the adult PVH, but not in the supraoptic nucleus, markedly increases body weight and food intake, with an elevated level of plasma triglyceride and leptin. Intraperitoneal administration of Oxt rescues the hyperphagic phenotype of the PVH Oxt cKO model. Furthermore, we show that cKO of Oxtr selectively in the posterior hypothalamic regions, especially the arcuate hypothalamic nucleus, a primary center for appetite regulations, phenocopies hyperphagic obesity. Collectively, these data reveal that Oxt signaling in the arcuate nucleus suppresses excessive food intake.

Ventromedial hypothalamic OGT drives adipose tissue lipolysis and curbs obesity

The ventromedial hypothalamus (VMH) is known to regulate body weight and counterregulatory response. However, how VMH neurons regulate lipid metabolism and energy balance remains unknown. O-linked β-d-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation), catalyzed by O-GlcNAc transferase (OGT), is considered a cellular sensor of nutrients and hormones. Here, we report that genetic ablation of OGT in VMH neurons inhibits neuronal excitability. Mice with VMH neuron-specific OGT deletion show rapid weight gain, increased adiposity, and reduced energy expenditure, without significant changes in food intake or physical activity. The obesity phenotype is associated with adipocyte hypertrophy and reduced lipolysis of white adipose tissues. In addition, OGT deletion in VMH neurons down-regulates the sympathetic activity and impairs the sympathetic innervation of white adipose tissues. These findings identify OGT in the VMH as a homeostatic set point that controls body weight and underscore the importance of the VMH in regulating lipid metabolism through white adipose tissue-specific innervation.

In Vivo Photometry Reveals Insulin and 2-Deoxyglucose Maintain Prolonged Inhibition of VMH Vglut2 Neurons in Male Mice

The ventromedial hypothalamic (VMH) nucleus is a well-established hub for energy and glucose homeostasis. In particular, VMH neurons are thought to be important for initiating the counterregulatory response to hypoglycemia, and ex vivo electrophysiology and immunohistochemistry data indicate a clear role for VMH neurons in sensing glucose concentration. However, the temporal response of VMH neurons to physiologically relevant changes in glucose availability in vivo has been hampered by a lack of available tools for measuring neuronal activity over time. Since the majority of neurons within the VMH are glutamatergic and can be targeted using the vesicular glutamate transporter Vglut2, we expressed cre-dependent GCaMP7s in Vglut2 cre mice and examined the response profile of VMH to intraperitoneal injections of glucose, insulin, and 2-deoxyglucose (2DG). We show that reduced available glucose via insulin-induced hypoglycemia and 2DG-induced glucoprivation, but not hyperglycemia induced by glucose injection, inhibits VMH Vglut2 neuronal population activity in vivo. Surprisingly, this inhibition was maintained for at least 45 minutes despite prolonged hypoglycemia and initiation of a counterregulatory response. Thus, although VMH stimulation, via pharmacological, electrical, or optogenetic approaches, is sufficient to drive a counterregulatory response, our data suggest VMH Vglut2 neurons are not the main drivers required to do so, since VMH Vglut2 neuronal population activity remains suppressed during hypoglycemia and glucoprivation.

The ventromedial hypothalamic nucleus: watchdog of whole-body glucose homeostasis

The brain, particularly the ventromedial hypothalamic nucleus (VMH), has been long known for its involvement in glucose sensing and whole-body glucose homeostasis. However, it is still not fully understood how the brain detects and responds to the changes in the circulating glucose levels, as well as brain-body coordinated control of glucose homeostasis. In this review, we address the growing evidence implicating the brain in glucose homeostasis, especially in the contexts of hypoglycemia and diabetes. In addition to neurons, we emphasize the potential roles played by non-neuronal cells, as well as extracellular matrix in the hypothalamus in whole-body glucose homeostasis. Further, we review the ionic mechanisms by which glucose-sensing neurons sense fluctuations of ambient glucose levels. We also introduce the significant implications of heterogeneous neurons in the VMH upon glucose sensing and whole-body glucose homeostasis, in which sex difference is also addressed. Meanwhile, research gaps have also been identified, which necessities further mechanistic studies in future.

The physiological control of eating: signals, neurons, and networks

During the past 30 yr, investigating the physiology of eating behaviors has generated a truly vast literature. This is fueled in part by a dramatic increase in obesity and its comorbidities that has coincided with an ever increasing sophistication of genetically based manipulations. These techniques have produced results with a remarkable degree of cell specificity, particularly at the cell signaling level, and have played a lead role in advancing the field. However, putting these findings into a brain-wide context that connects physiological signals and neurons to behavior and somatic physiology requires a thorough consideration of neuronal connections: a field that has also seen an extraordinary technological revolution. Our goal is to present a comprehensive and balanced assessment of how physiological signals associated with energy homeostasis interact at many brain levels to control eating behaviors. A major theme is that these signals engage sets of interacting neural networks throughout the brain that are defined by specific neural connections. We begin by discussing some fundamental concepts, including ones that still engender vigorous debate, that provide the necessary frameworks for understanding how the brain controls meal initiation and termination. These include key word definitions, ATP availability as the pivotal regulated variable in energy homeostasis, neuropeptide signaling, homeostatic and hedonic eating, and meal structure. Within this context, we discuss network models of how key regions in the endbrain (or telencephalon), hypothalamus, hindbrain, medulla, vagus nerve, and spinal cord work together with the gastrointestinal tract to enable the complex motor events that permit animals to eat in diverse situations.

Hypothalamic control of energy expenditure and thermogenesis

Energy expenditure and energy intake need to be balanced to maintain proper energy homeostasis. Energy homeostasis is tightly regulated by the central nervous system, and the hypothalamus is the primary center for the regulation of energy balance. The hypothalamus exerts its effect through both humoral and neuronal mechanisms, and each hypothalamic area has a distinct role in the regulation of energy expenditure. Recent studies have advanced the understanding of the molecular regulation of energy expenditure and thermogenesis in the hypothalamus with targeted manipulation techniques of the mouse genome and neuronal function. In this review, we elucidate recent progress in understanding the mechanism of how the hypothalamus affects basal metabolism, modulates physical activity, and adapts to environmental temperature and food intake changes.

The hypothalamus is a key regulator of metabolism, controlling resting metabolism, activity levels, and responses to external temperature and food intake. The balance between energy intake and expenditure must be tightly controlled, with imbalances resulting in metabolic disorders such as obesity or diabetes. Obin Kwon at Seoul National University College of Medicine and Ki Woo Kim at Yonsei University College of Dentistry, Seoul, both in South Korea, and coworkers reviewed how metabolism is regulated by the hypothalamus, a small hormone-producing brain region. They report that hormonal and neuronal signals from the hypothalamus influence the ratio of lean to fatty tissue, gender-based differences in metabolism, activity levels, and weight gain in response to food intake. They note that further studies to untangle cause-and-effect relationships and other genetic factors will improve our understanding of metabolic regulation.

Neural and Genetic Basis of Evasion, Approach and Predation

Evasion, approach and predation are examples of innate behaviour that are fundamental for the survival of animals. Uniting these behaviours is the assessment of threat, which is required to select between these options. Far from being comprehensive, we give a broad review over recent studies utilising optic techniques that have identified neural circuits and genetic identities underlying these behaviours.

Immunohistochemical Analysis of Neurotransmitters in Neurosecretory Protein GL-Producing Neurons of the Mouse Hypothalamus

We recently discovered a novel neuropeptide of 80 amino acid residues: neurosecretory protein GL (NPGL), in the hypothalamus of birds and rodents. NPGL is localized in the lateral posterior part of the arcuate nucleus (ArcLP), and it enhances feeding behavior and fat accumulation in mice. Various neurotransmitters, such as catecholamine, glutamate, and γ-aminobutyric acid (GABA), produced in the hypothalamus are also involved in energy metabolism. The colocalization of neurotransmitters and NPGL in neurons of the ArcLP leads to the elucidation of the regulatory mechanism of NPGL neurons. In this study, we performed double immunofluorescence staining to elucidate the relationship between NPGL and neurotransmitters in mice. The present study revealed that NPGL neurons did not co-express tyrosine hydroxylase as a marker of catecholaminergic neurons and vesicular glutamate transporter-2 as a marker of glutamatergic neurons. In contrast, NPGL neurons co-produced glutamate decarboxylase 67, a marker for GABAergic neurons. In addition, approximately 50% of NPGL neurons were identical to GABAergic neurons. These results suggest that some functions of NPGL neurons may be related to those of GABA. This study provides insights into the neural network of NPGL neurons that regulate energy homeostasis, including feeding behavior and fat accumulation.

Running the Female Power Grid Across Lifespan Through Brain Estrogen Signaling

The role of central estrogen in cognitive, metabolic, and reproductive health has long fascinated the lay public and scientists alike. In the last two decades, insight into estrogen signaling in the brain and its impact on female physiology is beginning to catch up with the vast information already established for its actions on peripheral tissues. Using newer methods to manipulate estrogen signaling in hormone-sensitive brain regions, neuroscientists are now identifying the molecular pathways and neuronal subtypes required for controlling sex-dependent energy allocation. However, the immense cellular complexity of these hormone-sensitive brain regions makes it clear that more research is needed to fully appreciate how estrogen modulates neural circuits to regulate physiological and behavioral end points. Such insight is essential for understanding how natural or drug-induced hormone fluctuations across lifespan affect women's health.

Advances in optogenetic studies of depressive-like behaviors and underlying neural circuit mechanisms

BACKGROUNDS

The neural circuit mechanisms underlying depression remain unclear. Recently optogenetics has gradually gained recognition as a novel technique to regulate the activity of neurons with light stimulation. Scientists are now transferring their focus to the function of brain regions and neural circuits in the pathogenic progress of depression. Deciphering the circuitry mechanism of depressive-like behaviors may help us better understand the symptomatology of depression. However, few studies have summarized current progress on optogenetic researches into the neural circuit mechanisms of depressive-like behaviors.

AIMS

This review aimed to introduce fundamental characteristics and methodologies of optogenetics, as well as how this technique achieves specific neuronal control with spatial and temporal accuracy. We mainly summarized recent progress in neural circuit discoveries in depressive-like behaviors using optogenetics and exhibited the potential of optogenetics as a tool to investigate the mechanism and possible optimization underlying antidepressant treatment such as ketamine and deep brain stimulation.

METHODS

A systematic review of the literature published in English mainly from 2010 to the present in databases was performed. The selected literature is then categorized and summarized according to their neural circuits and depressive-like behaviors.

CONCLUSIONS

Many important discoveries have been made utilizing optogenetics. These findings support optogenetics as a powerful and potential tool for studying depression. And our comprehension to the etiology of depression and other psychiatric disorders will also be more thorough with this rapidly developing technique in the near future.

Cav3.1-driven bursting firing in ventromedial hypothalamic neurons exerts dual control of anxiety-like behavior and energy expenditure

The central nervous system has evolved to coordinate the regulation of both the behavior response to the external environment and homeostasis of energy expenditure. Recent studies have indicated the dorsomedial ventromedial hypothalamus (dmVMH) as an important hub that regulates both innate behavior and energy homeostasis for coping stress. However, how dmVMH neurons control neuronal firing pattern to regulate chronic stress-induced anxiety and energy expenditure remains poorly understood. Here, we found enhanced neuronal activity in VMH after chronic stress, which is mainly induced by increased proportion of burst firing neurons. This enhancement of VMH burst firing is predominantly mediated by Cav3.1 expression. Optogenetically evoked burst firing of dmVMH neurons induced anxiety-like behavior, shifted the respiratory exchange ratio toward fat oxidation, and decreased food intake, while knockdown of Cav3.1 in the dmVMH had the opposite effects, suggested that Cav 3.1 as a crucial regulator. Interestingly, we found that fluoxetine (anxiolytics) could block the increase of Cav3.1 expression to inhibit the burst firing, and then rescued the anxiety-like behaviors and energy expenditure changes. Collectively, our study first revealed an important role of Cav3.1-driven bursting firing of dmVMH neurons in the control of anxiety-like behavior and energy expenditure, and provided potential therapeutic targets for treating the chronic stress-induced emotional malfunction and metabolism disorders.

Ventromedial Hypothalamus Activation Aggravates Hypertension Myocardial Remodeling Through the Sympathetic Nervous System

Background: The ventromedial hypothalamus (VMH) is an important nuclei in responding to emotional stress, and emotional stress is a risk factor for cardiovascular diseases. However, the role of the VMH in cardiovascular diseases remains unknown. This study aimed to investigate the effects and underlying mechanisms of VMH activation on hypertension related cardiac remodeling in two-kidney-one-clip (2K1C) hypertension (HTN) rats. Methods: Eighteen male Sprague-Dawley rats were injected with AAV-hSyn-hM3D(Gq) into the VMH at 0 weeks and then randomly divided into three groups: (1) sham group (sham 2K1C + saline i.p. injection); (2) HTN group (2K1C + saline i.p. injection); (3) HTN+VMH activation group (2K1C + clozapine-N-oxide i.p. injection). One week later, rats were subjected to a sham or 2K1C operation, and 2 weeks later rats were injected with clozapine-N-oxide or saline for 2 weeks. Results: In the HTN+VMH activation group, FosB expression was significantly increased in VMH sections compared with those of the other two groups. Compared to the HTN group, the HTN+VMH activation group showed significant: (1) increases in systolic blood pressure (SBP); (2) exacerbation of cardiac remodeling; and (3) increases in serum norepinephrine levels and sympathetic indices of heart rate variability. Additionally, myocardial RNA-sequencing analysis showed that VMH activation might regulate the HIF-1 and PPAR signal pathway and fatty acid metabolism. qPCR results confirmed that the relative mRNA expression of HIF-1α was increased and the PPARα and CPT-1 mRNA expression were decreased in the HTN+VMH activation group compared to the HTN group. Conclusions: VMH activation could increase SBP and aggravate cardiac remodeling possibly by sympathetic nerve activation and the HIF-1α/PPARα/CPT-1 signaling pathway might be the underlying mechanism.

Miniature microscopes for manipulating and recording in vivo brain activity

Here we describe the development and application of miniature integrated microscopes (miniscopes) paired with microendoscopes that allow for the visualization and manipulation of neural circuits in superficial and subcortical brain regions in freely behaving animals. Over the past decade the miniscope platform has expanded to include simultaneous optogenetic capabilities, electrically-tunable lenses that enable multi-plane imaging, color-corrected optics, and an integrated data acquisition platform that streamlines multimodal experiments. Miniscopes have given researchers an unprecedented ability to monitor hundreds to thousands of genetically-defined neurons from weeks to months in both healthy and diseased animal brains. Sophisticated algorithms that take advantage of constrained matrix factorization allow for background estimation and reliable cell identification, greatly improving the reliability and scalability of source extraction for large imaging datasets. Data generated from miniscopes have empowered researchers to investigate the neural circuit underpinnings of a wide array of behaviors that cannot be studied under head-fixed conditions, such as sleep, reward seeking, learning and memory, social behaviors, and feeding. Importantly, the miniscope has broadened our understanding of how neural circuits can go awry in animal models of progressive neurological disorders, such as Parkinson's disease. Continued miniscope development, including the ability to record from multiple populations of cells simultaneously, along with continued multimodal integration of techniques such as electrophysiology, will allow for deeper understanding into the neural circuits that underlie complex and naturalistic behavior.

Ventromedial Nucleus of the Hypothalamus Neurons Under the Magnifying Glass

The ventromedial nucleus of the hypothalamus (VMH) is a complex brain structure that is integral to many neuroendocrine functions, including glucose regulation, thermogenesis, and appetitive, social, and sexual behaviors. As such, it is of little surprise that the nucleus is under intensive investigation to decipher the mechanisms which underlie these diverse roles. Developments in genetic and investigative tools, for example the targeting of steroidogenic factor-1-expressing neurons, have allowed us to take a closer look at the VMH, its connections, and how it affects competing behaviors. In the current review, we aim to integrate recent findings into the literature and contemplate the conclusions that can be drawn.

An Inhibitory Medial Preoptic Circuit Mediates Innate Exploration

Animals have an innate motivation to explore objects and environments with unknown values. To this end, they need to activate neural pathways that enable exploration. Here, we reveal that photostimulation of a subset of medial preoptic area (MPA) neurons expressing the vesicular-GABA transporter gene (vgat+) and sending axonal projections to the ventrolateral periaqueductal gray (vPAG) increases exploration in a chamber but causes no place preference when tested there without photostimulation. Photoinhibition of MPA^vgat–vPAG projections leads to no emotional changes as measured by normal activity in an open field assay. Electrophysiological recordings revealed that most GABAergic vPAG neurons are inhibited by MPA^vgat neurons. In contrast to a previous report that suggested that MPA^vgat–vPAG neurons may impart positive valence to induce place preference, our results suggest that these neurons can increase innate exploration.

Loss of CREB Coactivator CRTC1 in SF1 Cells Leads to Hyperphagia and Obesity by High-fat Diet But Not Normal Chow Diet

Cyclic adenosine monophosphate responsive element-binding protein-1-regulated transcription coactivator-1 (CRTC1) is a cytoplasmic coactivator that translocates to the nucleus in response to cyclic adenosine monophosphate. Whole-body knockdown of Crtc1 causes obesity, resulting in increased food intake and reduced energy expenditure. CRTC1 is highly expressed in the brain; therefore, it might play an important role in energy metabolism via the neuronal pathway. However, the precise mechanism by which CRTC1 regulates energy metabolism remains unknown. Here, we showed that mice lacking CRTC1, specifically in steroidogenic factor-1 expressing cells (SF1 cells), were sensitive to high-fat diet (HFD)-induced obesity, exhibiting hyperphagia and increased body weight gain. The loss of CRTC1 in SF1 cells impaired glucose metabolism. Unlike whole-body CRTC1 knockout mice, SF1 cell-specific CRTC1 deletion did not affect body weight gain or food intake in normal chow feeding. Thus, CRTC1 in SF1 cells is required for normal appetite regulation in HFD-fed mice. CRTC1 is primarily expressed in the brain. Within the hypothalamus, which plays an important role for appetite regulation, SF1 cells are only found in ventromedial hypothalamus. RNA sequencing analysis of microdissected ventromedial hypothalamus samples revealed that the loss of CRTC1 significantly changed the expression levels of certain genes. Our results revealed the important protective role of CRTC1 in SF1 cells against dietary metabolic imbalance.

Rap1 in the VMH regulates glucose homeostasis

The hypothalamus is a critical regulator of glucose metabolism and is capable of correcting diabetes conditions independently of an effect on energy balance. The small GTPase Rap1 in the forebrain is implicated in high-fat diet–induced (HFD-induced) obesity and glucose imbalance. Here, we report that increasing Rap1 activity selectively in the medial hypothalamus elevated blood glucose without increasing the body weight of HFD-fed mice. In contrast, decreasing hypothalamic Rap1 activity protected mice from diet-induced hyperglycemia but did not prevent weight gain. The remarkable glycemic effect of Rap1 was reproduced when Rap1 was specifically deleted in steroidogenic factor-1–positive (SF-1–positive) neurons in the ventromedial hypothalamic nucleus (VMH) known to regulate glucose metabolism. While having no effect on body weight regardless of sex, diet, and age, Rap1 deficiency in the VMH SF1 neurons markedly lowered blood glucose and insulin levels, improved glucose and insulin tolerance, and protected mice against HFD-induced neural leptin resistance and peripheral insulin resistance at the cellular and whole-body levels. Last, acute pharmacological inhibition of brain exchange protein directly activated by cAMP 2, a direct activator of Rap1, corrected glucose imbalance in obese mouse models. Our findings uncover the primary role of VMH Rap1 in glycemic control and implicate Rap1 signaling as a potential target for therapeutic intervention in diabetes.

New Insights of SF1 Neurons in Hypothalamic Regulation of Obesity and Diabetes

Despite the substantial role played by the hypothalamus in the regulation of energy balance and glucose homeostasis, the exact mechanisms and neuronal circuits underlying this regulation remain poorly understood. In the last 15 years, investigations using transgenic models, optogenetic, and chemogenetic approaches have revealed that SF1 neurons in the ventromedial hypothalamus are a specific lead in the brain’s ability to sense glucose levels and conduct insulin and leptin signaling in energy expenditure and glucose homeostasis, with minor feeding control. Deletion of hormonal receptors, nutritional sensors, or synaptic receptors in SF1 neurons triggers metabolic alterations mostly appreciated under high-fat feeding, indicating that SF1 neurons are particularly important for metabolic adaptation in the early stages of obesity. Although these studies have provided exciting insight into the implications of hypothalamic SF1 neurons on whole-body energy homeostasis, new questions have arisen from these results. Particularly, the existence of neuronal sub-populations of SF1 neurons and the intricate neurocircuitry linking these neurons with other nuclei and with the periphery. In this review, we address the most relevant studies carried out in SF1 neurons to date, to provide a global view of the central role played by these neurons in the pathogenesis of obesity and diabetes.

Optogenetic fUSI for brain-wide mapping of neural activity mediating collicular-dependent behaviors

Neuronal cell types are arranged in brain-wide circuits that guide behavior. In mice, the superior colliculus innervates a set of targets that direct orienting and defensive actions. We combined functional ultrasound imaging (fUSI) with optogenetics to reveal the network of brain regions functionally activated by four collicular cell types. Stimulating each neuronal group triggered different behaviors and activated distinct sets of brain nuclei. This included regions not previously thought to mediate defensive behaviors, for example, the posterior paralaminar nuclei of the thalamus (PPnT), which we show to play a role in suppressing habituation. Neuronal recordings with Neuropixels probes show that (1) patterns of spiking activity and fUSI signals correlate well in space and (2) neurons in downstream nuclei preferentially respond to innately threatening visual stimuli. This work provides insight into the functional organization of the networks governing innate behaviors and demonstrates an experimental approach to explore the whole-brain neuronal activity downstream of targeted cell types.

Hypothalamic insulin signalling as a nexus regulating mood and metabolism

Insulin has long been known as a metabolic hormone critical in the treatment of diabetes for its peripheral effects on blood glucose. However, in the last 50 years, insulin has entered the realm of neuroendocrinology and many studies have described its function on insulin receptors in the brain in relation to both metabolic and mood disorders. Indeed, rodent models of impaired insulin signalling show signs of dysregulated energy and glucose homeostasis, as well as anxiety-like and depressive behaviours. Importantly, many metabolic diseases such as obesity and diabetes increase the risk of developing mood disorders; however, the brain mechanisms underlying the connection between metabolism and mood remain unresolved. We present the current literature on the importance of the insulin receptor with respect to regulating glucose and energy homeostasis and mood-related behaviours. Specifically, we hypothesise that the insulin receptor in the hypothalamus, classically known as the homeostatic centre of the brain, plays a causal role in linking metabolic and behavioural effects of insulin signalling. In this review, we discuss insulin signalling in the hypothalamus as a critical point of neural integration controlling metabolism and mood.

Defective autophagy in Sf1 neurons perturbs the metabolic response to fasting and causes mitochondrial dysfunction

Objective

The ventromedial nucleus of the hypothalamus (VMH) is a critical component of the forebrain pathways that regulate energy homeostasis. It also plays an important role in the metabolic response to fasting. However, the mechanisms contributing to these physiological processes remain elusive. Autophagy is an evolutionarily conserved mechanism that maintains cellular homeostasis by turning over cellular components and providing nutrients to the cells during starvation. Here, we investigated the importance of the autophagy-related gene Atg7 in Sf1-expressing neurons of the VMH in control and fasted conditions.

Methods

We generated Sf1-Cre; Atg7^loxP/loxP mice and examined their metabolic and cellular response to fasting.

Results

Fasting induces autophagy in the VMH, and mice lacking Atg7 in Sf1-expressing neurons display altered leptin sensitivity and impaired energy expenditure regulation in response to fasting. Moreover, loss of Atg7 in Sf1 neurons causes alterations in the central response to fasting. Furthermore, alterations in mitochondria morphology and activity are observed in mutant mice.

Conclusion

Together, these data show that autophagy is nutritionally regulated in VMH neurons and that VMH autophagy participates in the control of energy homeostasis during fasting.

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Fasting induces autophagy in the ventromedial nucleus of the hypothalamus.

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Genetic loss of Atg7 in the VMH impairs metabolic response to fasting.

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Mice lacking Atg7 in the VMH display impaired mitochondria morphology and activity.

Hypothalamic hormone-sensitive lipase regulates appetite and energy homeostasis

Objective

The goal of this study was to investigate the importance of central hormone-sensitive lipase (HSL) expression in the regulation of food intake and body weight in mice to clarify whether intracellular lipolysis in the mammalian hypothalamus plays a role in regulating appetite.

Methods

Using pharmacological and genetic approaches, we investigated the role of HSL in the rodent brain in the regulation of feeding and energy homeostasis under basal conditions during acute stress and high-fat diet feeding.

Results

We found that HSL, a key enzyme in the catabolism of cellular lipid stores, is expressed in the appetite-regulating centers in the hypothalamus and is activated by acute stress through a mechanism similar to that observed in adipose tissue and skeletal muscle. Inhibition of HSL in rodent models by a synthetic ligand, global knockout, or brain-specific deletion of HSL prevents a decrease in food intake normally seen in response to acute stress and is associated with the increased expression of orexigenic peptides neuropeptide Y (NPY) and agouti-related peptide (AgRP). Increased food intake can be reversed by adeno-associated virus-mediated reintroduction of HSL in neurons of the mediobasal hypothalamus. Importantly, metabolic stress induced by a high-fat diet also enhances the hyperphagic phenotype of HSL-deficient mice. Specific deletion of HSL in the ventromedial hypothalamic nucleus (VMH) or AgRP neurons reveals that HSL in the VMH plays a role in both acute stress-induced food intake and high-fat diet-induced obesity.

Conclusions

Our results indicate that HSL activity in the mediobasal hypothalamus is involved in the acute reduction in food intake during the acute stress response and sensing of a high-fat diet.

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HSL is expressed in appetite-regulating nuclei of the mouse hypothalamus.

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HSL in the hypothalamus is activated via β-adrenergic receptor signaling.

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The anorexic response to acute stress is blunted in mice without hypothalamic HSL.

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Central HSL deficiency results in obesity in mice on a high-fat diet.

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HSL in SF1-positive neurons contributes to the anorexigenic stress response.

Energy state alters regulation of proopiomelanocortin neurons by glutamatergic ventromedial hypothalamus neurons: pre- and postsynaptic mechanisms

To maintain metabolic homeostasis, motivated behaviors are driven by neuronal circuits that process information encoding the animal's energy state. Such circuits likely include ventromedial hypothalamus (VMH) glutamatergic neurons that project throughout the brain to drive food intake and energy expenditure. Targets of VMH glutamatergic neurons include proopiomelanocortin (POMC) neurons in the arcuate nucleus that, when activated, inhibit food intake. Although an energy-state-sensitive, glutamate circuit between the VMH and POMC neurons has been previously indicated, the significance and details of this circuit have not been fully elucidated. Thus, the goal of the present work was to add to the understanding of this circuit. Using a knockout strategy, the data show that the VMH glutamate→POMC neuron circuit is important for the inhibition of food intake. Conditional deletion of the vesicular glutamate transporter (VGLUT2) in the VMH results in increased bodyweight and increased food intake following a fast in both male and female mice. Additionally, the targeted blunting of glutamate release from the VMH resulted in an ∼32% reduction in excitatory inputs to POMC cells, suggesting that this circuit may respond to changes in energy state to affect POMC activity. Indeed, we found that glutamate release is increased at VMH-to-POMC synapses during feeding and POMC AMPA receptors switch from a calcium-permeable state to a calcium-impermeable state during fasting. Collectively, these data indicate that there is an energy-balance-sensitive VMH-to-POMC circuit conveying excitatory neuromodulation onto POMC cells at both pre- and postsynaptic levels, which may contribute to maintaining appropriate food intake and body mass.NEW & NOTEWORTHY Despite decades of research, the neurocircuitry underlying metabolic homeostasis remains incompletely understood. Specifically, the roles of amino acid transmitters, particularly glutamate, have received less attention than hormonal signals. Here, we characterize an energy-state-sensitive glutamate circuit from the ventromedial hypothalamus to anorexigenic proopiomelanocortin (POMC) neurons that responds to changes in energy state at both sides of the synapse, providing novel information about how variations in metabolic state affect excitatory drive onto POMC cells.

Electroconvulsive seizures lead to lipolytic-induced gene expression changes in mediobasal hypothalamus and decreased white adipose tissue mass

Aims

Electroconvulsive seizure (ECS) therapy is highly effective in the treatment of several psychiatric disorders, including depression. Past studies have shown that the rodent model of ECS reveals the activation of multiple brain regions including the hypothalamus, suggesting that this method of brain stimulation broadly regulates central neuronal function, which results in peripheral function. The ventromedial nucleus of the hypothalamus (VMH) plays an important role in feeding and energy homeostasis. Our previous study showed that ECS increases the expression of anorexigenic factors in the VMH and has an anorexigenic effect in a mouse model. Since the VMH is also suggested to play a critical role in the peripheral lipid metabolism of white adipose tissue (WAT), we hypothesized that ECS alters lipid metabolism via activation of the VMH.

Methods and Results

Here, we demonstrate that repeated ECS suppresses the fat mass of epididymal WAT and significantly increases the expression levels of lipolytic and brown adipose tissue markers such as Adrb3, Hsl/Lipe, and Ppargc1a. In the VMH, ECS increased the expression of multiple genes, notably Bdnf, Adcyap1, and Crhr2, which are not only anorexigenic factors but are also modulators of lipid metabolism. Furthermore, gold‐thioglucose‐induced hypothalamic lesions affecting the VMH abolished the effect of ECS on the WAT, indicating that hypothalamus activation is required for the phenotypic changes seen in the epididymal WAT.

Conclusion

Our data demonstrates a new effect of ECS on the lipid metabolism of WAT via induction of hypothalamic activity involving the VMH.

In the present study, we demonstrated that ECS exerts effects on adipose tissue and suggest the requirement of the hypothalamus, including the VMH, for the lipolytic effect of ECS.

An excitatory ventromedial hypothalamus to paraventricular thalamus circuit that suppresses food intake

It is well recognized that ventromedial hypothalamus (VMH) serves as a satiety center in the brain. However, the feeding circuit for the VMH regulation of food intake remains to be defined. Here, we combine fiber photometry, chemo/optogenetics, virus-assisted retrograde tracing, ChR2-assisted circuit mapping and behavioral assays to show that selective activation of VMH neurons expressing steroidogenic factor 1 (SF1) rapidly inhibits food intake, VMH SF1 neurons project dense fibers to the paraventricular thalamus (PVT), selective chemo/optogenetic stimulation of the PVT-projecting SF1 neurons or their projections to the PVT inhibits food intake, and chemical genetic inactivation of PVT neurons diminishes SF1 neural inhibition of feeding. We also find that activation of SF1 neurons or their projections to the PVT elicits a flavor aversive effect, and selective optogenetic stimulation of ChR2-expressing SF1 projections to the PVT elicits direct excitatory postsynaptic currents. Together, our data reveal a neural circuit from VMH to PVT that inhibits food intake.

The ventromedial hypothalamus (VMH) serves as a satiety center in the brain, however, the neural circuits involved are incompletely understood. Here, the authors decipher a neural circuit from VMH to the paraventricular thalamus that suppresses food intake.