An approximate line attractor in the hypothalamus encodes an aggressive state.

The hypothalamus regulates innate social behaviors, including mating and aggression. These behaviors can be evoked by optogenetic stimulation of specific neuronal subpopulations within MPOA and VMHvl, respectively. Here, we perform dynamical systems modeling of population neuronal activity in these nuclei during social behaviors. In VMHvl, unsupervised analysis identified a dominant dimension of neural activity with a large time constant (>50 s), generating an approximate line attractor in neural state space. Progression of the neural trajectory along this attractor was correlated with an escalation of agonistic behavior, suggesting that it may encode a scalable state of aggressiveness. Consistent with this, individual differences in the magnitude of the integration dimension time constant were strongly correlated with differences in aggressiveness. In contrast, approximate line attractors were not observed in MPOA during mating; instead, neurons with fast dynamics were tuned to specific actions. Thus, different hypothalamic nuclei employ distinct neural population codes to represent similar social behaviors.

A developmental switch between electrical and neuropeptide communication in the ventromedial hypothalamus.

Dissecting neural connectivity patterns within local brain regions is an essential step to understanding the function of the brain.1 Neural microcircuits in brain regions, such as the neocortex and the hippocampus, have been extensively studied.2 By contrast, the microcircuit in the hypothalamus remains largely uncharacterized. The hypothalamus is crucial for animals' survival and reproduction.3 Knowledge of how different hypothalamic nuclei coordinate with each other and outside brain regions for hypothalamus-related functions has been significantly advanced.4-9 Although there are limited studies on the neural microcircuit in the lateral hypothalamus (LHA)10,11 and the suprachiasmatic nucleus (SCN),12,13 the patterns of neural microcircuits in most of the given hypothalamic nuclei remain largely unknown. This study applied combinatory approaches to address the local neural circuit pattern in the ventromedial hypothalamus (VMH) and other hypothalamic nuclei. We discovered a unique neural circuit design in the VMH. Neurons in the VMH were electrically coupled at the early postnatal stage like ones in the neocortex.14 However, unlike neocortical neurons,14,15 they developed very few chemical synapses after the disappearance of electrical synapses. Instead, VMH neurons communicated with neuropeptides. The similar scarceness of synaptic connectivity found in other hypothalamic nuclei further indicated that the lack of synaptic connections is a unique feature for local neural circuits in most adult hypothalamic nuclei. Thus, our findings provide a solid synaptic basis at the cellular level to understand hypothalamic functions better.

Neural circuit mechanisms that govern inter-male attack in mice.

Individuals of many species fight with conspecifics to gain access to or defend critical resources essential for survival and reproduction. Such intraspecific fighting is evolutionarily selected for in a species-, sex-, and environment-dependent manner when the value of resources secured exceeds the cost of fighting. One such example is males fighting for chances to mate with females. Recent advances in new tools open up ways to dissect the detailed neural circuit mechanisms that govern intraspecific, particularly inter-male, aggression in the model organism Mus musculus (house mouse). By targeting and functional manipulating genetically defined populations of neurons and their projections, these studies reveal a core neural circuit that controls the display of reactive male-male attacks in mice, from sensory detection to decision making and action selection. Here, we summarize these critical results. We then describe various modulatory inputs that route into the core circuit to afford state-dependent and top-down modulation of inter-male attacks. While reviewing these exciting developments, we note that how the inter-male attack circuit converges or diverges with neural circuits that mediate other forms of social interactions remain not fully understood. Finally, we emphasize the importance of combining circuit, pharmacological, and genetic analysis when studying the neural control of aggression in the future.

Oestrogen engages brain MC4R signalling to drive physical activity in female mice.

Oestrogen depletion in rodents and humans leads to inactivity, fat accumulation and diabetes1,2, underscoring the conserved metabolic benefits of oestrogen that inevitably decrease with age. In rodents, the preovulatory surge in 17ß-oestradiol (E2) temporarily increases energy expenditure to coordinate increased physical activity with peak sexual receptivity. Here we report that a subset of oestrogen-sensitive neurons in the ventrolateral ventromedial hypothalamic nucleus (VMHvl)3-7 projects to arousal centres in the hippocampus and hindbrain, and enables oestrogen to rebalance energy allocation in female mice. Surges in E2 increase melanocortin-4 receptor (MC4R) signalling in these VMHvl neurons by directly recruiting oestrogen receptor-α (ERα) to the Mc4r gene. Sedentary behaviour and obesity in oestrogen-depleted female mice were reversed after chemogenetic stimulation of VMHvl neurons expressing both MC4R and ERα. Similarly, a long-term increase in physical activity is observed after CRISPR-mediated activation of this node. These data extend the effect of MC4R signalling - the most common cause of monogenic human obesity8 - beyond the regulation of food intake and rationalize reported sex differences in melanocortin signalling, including greater disease severity of MC4R insufficiency in women9. This hormone-dependent node illuminates the power of oestrogen during the reproductive cycle in motivating behaviour and maintaining an active lifestyle in women.

Kisspeptin signaling and nNOS neurons in the VMHvl modulate lordosis behavior but not mate preference in female mice.

It was recently shown that kisspeptin neurons in the anteroventral periventricular area (AVPV) orchestrate female sexual behavior, including lordosis behavior and mate preference. A potential target of AVPV kisspeptin signaling could be neurons expressing the neuronal form of nitric oxide synthase (nNOS) in the ventrolateral part of the ventromedial hypothalamus (VMHvl). Therefore, in the present study, we further refined the role of the VHMvl in female sexual behavior. Adult female mice received a bilateral cannula aimed at the VMHvl. A single injection with kisspeptin (Kp-10) or SNAP/BAY, a nitric oxide donor, significantly increased lordosis, whereas the nNOS inhibitor l-NAME decreased it. None of these drugs affected mate preference. Interestingly, administration of GnRH into the VMHvl had no effect on lordosis or mate preference. To determine whether the stimulatory effect of Kp-10 on lordosis was specific to the VMHvl, an additional group of females received Kp-10 directly into the paraventricular nucleus (PVN). No effect was found on lordosis and mate preference. These results suggest that kisspeptin most likely modulates lordosis behavior through nNOS neurons in the VMHvl whereas mate preference is modulated by kisspeptin through a separate neuronal circuit not including the VMHvl.

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.

Spike Activity in the Ventromedial Nucleus of Rat Hypothalamus during Aging.

Spike activity of neurons in the ventromedial nucleus (VMN) of the hypothalamus in adult (6-8 months) and aged (2 years) male rats was studied by the in vivo extracellular method using stereotaxic insertion of microelectrodes. In all animals, firing frequency of most VMN neurons increased in response to glucose administration. However, in aged rats, the mean baseline and glucose-induced spike frequencies of VMN neurons were lower than in adult animals. These results support the hypothesis that aging is associated with a decrease in the functional activity of hypothalamic neurons.

A hypothalamic-thalamostriatal circuit that controls approach-avoidance conflict in rats.

Survival depends on a balance between seeking rewards and avoiding potential threats, but the neural circuits that regulate this motivational conflict remain largely unknown. Using an approach-food vs. avoid-predator threat conflict test in rats, we identified a subpopulation of neurons in the anterior portion of the paraventricular thalamic nucleus (aPVT) which express corticotrophin-releasing factor (CRF) and are preferentially recruited during conflict. Inactivation of aPVTCRF neurons during conflict biases animal's response toward food, whereas activation of these cells recapitulates the food-seeking suppression observed during conflict. aPVTCRF neurons project densely to the nucleus accumbens (NAc), and activity in this pathway reduces food seeking and increases avoidance. In addition, we identified the ventromedial hypothalamus (VMH) as a critical input to aPVTCRF neurons, and demonstrated that VMH-aPVT neurons mediate defensive behaviors exclusively during conflict. Together, our findings describe a hypothalamic-thalamostriatal circuit that suppresses reward-seeking behavior under the competing demands of avoiding threats.

Cross-species analysis defines the conservation of anatomically segregated VMH neuron populations.

The ventromedial hypothalamic nucleus (VMH) controls diverse behaviors and physiologic functions, suggesting the existence of multiple VMH neural subtypes with distinct functions. Combing translating ribosome affinity purification with RNA-sequencing (TRAP-seq) data with single-nucleus RNA-sequencing (snRNA-seq) data, we identified 24 mouse VMH neuron clusters. Further analysis, including snRNA-seq data from macaque tissue, defined a more tractable VMH parceling scheme consisting of six major genetically and anatomically differentiated VMH neuron classes with good cross-species conservation. In addition to two major ventrolateral classes, we identified three distinct classes of dorsomedial VMH neurons. Consistent with previously suggested unique roles for leptin receptor (Lepr)-expressing VMH neurons, Lepr expression marked a single dorsomedial class. We also identified a class of glutamatergic VMH neurons that resides in the tuberal region, anterolateral to the neuroanatomical core of the VMH. This atlas of conserved VMH neuron populations provides an unbiased starting point for the analysis of VMH circuitry and function.

STAT3 but Not ERK2 Is a Crucial Mediator Against Diet-Induced Obesity via VMH Neurons.

Leptin plays an important role in the protection against diet-induced obesity (DIO) by its actions in ventromedial hypothalamic (VMH) neurons. However, little is known about the intracellular mechanisms involved in these effects. To assess the role of the STAT3 and ERK2 signaling in neurons that express the steroidogenic factor 1 (SF1) in the VMH in energy homeostasis, we used cre-lox technology to generate male and female mice with specific disruption of STAT3 or ERK2 in SF1 neurons of the VMH. We demonstrated that the conditional knockout of STAT3 in SF1 neurons of the VMH did not affect body weight, food intake, energy expenditure, or glucose homeostasis in animals on regular chow. However, with high-fat diet (HFD) challenge, loss of STAT3 in SF1 neurons caused a significant increase in body weight, food intake, and energy efficiency that was more remarkable in females, which also showed a decrease in energy expenditure. In contrast, deletion of ERK2 in SF1 neurons of VMH did not have any impact on energy homeostasis in both regular diet and HFD conditions. In conclusion, STAT3 but not ERK2 signaling in SF1 neurons of VMH plays a crucial role in protection against DIO in a sex-specific pattern.

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.

Sympathetic nervous system contributes to orthodontic tooth movement by central neural regulation from hypothalamus.

Orthodontic tooth movement (OTM) is a specific treatment of malocclusion, whose regulation mechanism is still not clear. This study aimed to reveal the relationship between the sympathetic nervous system (SNS) and OTM through the construction of an OTM rat model through the utilization of orthodontic nickeltitanium coiled springs. The results indicated that the stimulation of SNS by dopamine significantly promote the OTM process represented by the much larger distance between the first and second molar compared with mere exertion of orthodontic force. Superior cervical ganglionectomy (SCGx) can alleviate this promotion effect, further proving the role of SNS in the process of OTM. Subsequently, the ability of orthodontic force to stimulate the center of the SNS was visualized by the tyrosin hydroxylase (TH) staining of neurons in ventromedial hypothalamic nucleus (VMH) and arcuate nucleus (ARC) of the hypothalamus, as well as the up-regulated expression of norepinephrine in local alveolar bone. Moreover, we also elucidated that the stimulation of SNS can promote osteoclast differentiation in periodontal ligament cells (PDLCs) and bone marrow-derived cells (BMCs) through regulation of receptor activator of nuclear factor-κB ligand (RANKL)/osteoprotegerin (OPG) system, thus promoting the OTM process. In conclusion, this study provided the first evidence for the involvement of the hypothalamus in the promotion effect of SNS on OTM. This work could provide a novel theoretical and experimental basis for further understanding of the molecular mechanism of OTM.

Sex-dimorphic neuroestradiol regulation of ventromedial hypothalamic nucleus glucoregulatory transmitter and glycogen metabolism enzyme protein expression in the rat.

BACKGROUND: Ventromedial hypothalamic nucleus (VMN) gluco-regulatory transmission is subject to sex-specific control by estradiol. The VMN is characterized by high levels of aromatase expression. METHODS: The aromatase inhibitor letrozole (LZ) was used with high-resolution microdissection/Western blot techniques to address the hypothesis that neuroestradiol exerts sex-dimorphic control of VMN neuronal nitric oxide synthase (nNOS) and glutamate decarboxylase65/67 (GAD) protein expression. Glycogen metabolism impacts VMN nNOS and GAD profiles; here, LZ treatment effects on VMN glycogen synthase (GS) and phosphorylase brain- (GPbb; glucoprivic-sensitive) and muscle (GPmm; norepinephrine-sensitive) variant proteins were examined. RESULTS: VMN aromatase protein content was similar between sexes. Intracerebroventricular LZ infusion of testes-intact male and ovariectomized, estradiol-replaced female rats blocked insulin-induced hypoglycemic (IIH) up-regulation of this profile. LZ exerted sex-contingent effects on basal VMN nNOS and GAD expression, but blocked IIH-induced NO stimulation and GAD suppression in each sex. Sex-contingent LZ effects on basal and hypoglycemic patterns of GPbb and GPmm expression occurred at distinctive levels of the VMN. LZ correspondingly down- or up-regulated baseline pyruvate recycling pathway marker protein expression in males (glutaminase) and females (malic enzyme-1), and altered INS effects on those proteins. CONCLUSIONS: Results infer that neuroestradiol is required in each sex for optimal VMN metabolic transmitter signaling of hypoglycemic energy deficiency. Sex differences in VMN GP variant protein levels and sensitivity to aromatase may correlate with sex-dimorphic glycogen mobilization during this metabolic stress. Neuroestradiol may also exert sex-specific effects on glucogenic amino acid energy yield by actions on distinctive enzyme targets in each sex.

Differential Encoding of Predator Fear in the Ventromedial Hypothalamus and Periaqueductal Grey.

The ventromedial hypothalamus is a central node of the mammalian predator defense network. Stimulation of this structure in rodents and primates elicits abrupt defensive responses, including flight, freezing, sympathetic activation, and panic, while inhibition reduces defensive responses to predators. The major efferent target of the ventromedial hypothalamus is the dorsal periaqueductal gray (dPAG), and stimulation of this structure also elicits flight, freezing, and sympathetic activation. However, reversible inhibition experiments suggest that the ventromedial hypothalamus and periaqueductal gray play distinct roles in the control of defensive behavior, with the former proposed to encode an internal state necessary for the motivation of defensive responses, while the latter serves as a motor pattern initiator. Here, we used electrophysiological recordings of single units in behaving male mice exposed to a rat to investigate the encoding of predator fear in the dorsomedial division of the ventromedial hypothalamus (VMHdm) and the dPAG. Distinct correlates of threat intensity and motor responses were found in both structures, suggesting a distributed encoding of sensory and motor features in the medial hypothalamic-brainstem instinctive network.SIGNIFICANCE STATEMENT Although behavioral responses to predatory threat are essential for survival, the underlying neuronal circuits remain undefined. Using single unit in vivo electrophysiological recordings in mice, we have identified neuronal populations in the medial hypothalamus and brainstem that encode defensive responses to a rat predator. We found that both structures encode both sensory as well as motor aspects of the behavior although with different kinetics. Our findings provide a framework for understanding how innate sensory cues are processed to elicit adaptive behavioral responses to threat and will help to identify targets for the pharmacological modulation of related pathologic behaviors.

Essential and sex-specific effects of mGluR5 in ventromedial hypothalamus regulating estrogen signaling and glucose balance.

The ventromedial hypothalamus (VMH) plays chief roles regulating energy and glucose homeostasis and is sexually dimorphic. We discovered that expression of metabotropic glutamate receptor subtype 5 (mGluR5) in the VMH is regulated by caloric status in normal mice and reduced in brain-derived neurotrophic factor (BDNF) mutants, which are severely obese and have diminished glucose balance control. These findings led us to investigate whether mGluR5 might act downstream of BDNF to critically regulate VMH neuronal activity and metabolic function. We found that mGluR5 depletion in VMH SF1 neurons did not affect energy balance regulation. However, it significantly impaired insulin sensitivity, glycemic control, lipid metabolism, and sympathetic output in females but not in males. These sex-specific deficits are linked to reductions in intrinsic excitability and firing rate of SF1 neurons. Abnormal excitatory and inhibitory synapse assembly and elevated expression of the GABAergic synthetic enzyme GAD67 also cooperate to decrease and potentiate the synaptic excitatory and inhibitory tone onto mutant SF1 neurons, respectively. Notably, these alterations arise from disrupted functional interactions of mGluR5 with estrogen receptors that switch the normally positive effects of estrogen on SF1 neuronal activity and glucose balance control to paradoxical and detrimental. The collective data inform an essential central mechanism regulating metabolic function in females and underlying the protective effects of estrogen against metabolic disease.

Divergent Neural Pathways Emanating from the Lateral Parabrachial Nucleus Mediate Distinct Components of the Pain Response.

The lateral parabrachial nucleus (lPBN) is a major target of spinal projection neurons conveying nociceptive input into supraspinal structures. However, the functional role of distinct lPBN efferents in diverse nocifensive responses have remained largely uncharacterized. Here we show that that the lPBN is required for escape behaviors and aversive learning to noxious stimulation. In addition, we find that two populations of efferent neurons from different regions of the lPBN collateralize to distinct targets. Activation of efferent projections to the ventromedial hypothalamus (VMH) or lateral periaqueductal gray (lPAG) drives escape behaviors, whereas activation of lPBN efferents to the bed nucleus stria terminalis (BNST) or central amygdala (CEA) generates an aversive memory. Finally, we provide evidence that dynorphin-expressing neurons, which span cytoarchitecturally distinct domains of the lPBN, are required for aversive learning.

Hierarchical Representations of Aggression in a Hypothalamic-Midbrain Circuit.

Although the ventromedial hypothalamus ventrolateral area (VMHvl) is now well established as a critical locus for the generation of conspecific aggression, its role is complex, with neurons responding during multiple phases of social interactions with both males and females. It has been previously unclear how the brain uses this complex multidimensional signal and coordinates a discrete action: the attack. Here, we find a hypothalamic-midbrain circuit that represents hierarchically organized social signals during aggression. Optogenetic-assisted circuit mapping reveals a preferential projection from VMHvlvGlut2 to lPAGvGlut2 cells, and inactivation of downstream lPAGvGlut2 populations results in aggression-specific deficits. lPAG neurons are selective for attack action and exhibit short-latency, time-locked spiking relative to the activity of jaw muscles during biting. Last, we find that this projection conveys male-biased signals from the VMHvl to downstream lPAGvGlut2 neurons that are sensitive to features of ongoing activity, suggesting that action selectivity is generated by a combination of pre- and postsynaptic mechanisms.

Selective sexual differentiation of neurone populations may contribute to sex-specific outputs of the ventromedial nucleus of the hypothalamus.

Sex differences among neurones in the ventrolateral region of the ventromedial hypothalamic nucleus (VMHvl) allow for the display of a diversity of sex-typical behaviours and physiological responses, ranging from mating behaviour to metabolism. Here, we review recent studies that interrogate the relationship between sex-typical responses and changes in cellular phenotypes. We discuss technologies that increase the resolution of molecular profiling or targeting of cell populations, including single-cell transcriptional profiling and conditional viral genetic approaches to manipulate neurone survival or activity. Overall, emerging studies indicate that sex-typical functions of the VMH may be mediated by phenotypically distinct and sexually differentiated neurone populations within the VMHvl. Future studies in this and other brain regions could exploit cell-type-specific tools to reveal the cell populations and molecular mediators that modulate sex-typical responses. Furthermore, cell-type-specific analyses of the effects of sexually differentiating factors, including sex hormones, can test the hypothesis that distinct cell types within a single brain region vary with respect to sexual differentiation.

Changes in neuronal activity across the mouse ventromedial nucleus of the hypothalamus in response to low glucose: Evaluation using an extracellular multi-electrode array approach.

The hypothalamic ventromedial nucleus (VMN) is involved in maintaining systemic glucose homeostasis. Neurophysiological studies in rodent brain slices have identified populations of VMN glucose-sensing neurones: glucose-excited (GE) neurones, cells which increased their firing rate in response to increases in glucose concentration, and glucose-inhibited (GI) neurones, which show a reduced firing frequency in response to increasing glucose concentrations. To date, most slice electrophysiological studies characterising VMN glucose-sensing neurones in rodents have utilised the patch clamp technique. Multi-electrode arrays (MEAs) are a state-of-the-art electrophysiological tool enabling the electrical activity of many cells to be recorded across multiple electrode sites (channels) simultaneously. We used a perforated MEA (pMEA) system to evaluate electrical activity changes across the dorsal-ventral extent of the mouse VMN region in response to alterations in glucose concentration. Because intrinsic (ie, direct postsynaptic sensing) and extrinsic (ie, presynaptically modulated) glucosensation were not discriminated, we use the terminology 'GE/presynaptically excited by an increase (PER)' and 'GI/presynaptically excited by a decrease (PED)' in the present study to describe responsiveness to changes in extracellular glucose across the mouse VMN. We observed that 15%-60% of channels were GE/PER, whereas 2%-7% were GI/PED channels. Within the dorsomedial portion of the VMN (DM-VMN), significantly more channels were GE/PER compared to the ventrolateral portion of the VMN (VL-VMN). However, GE/PER channels within the VL-VMN showed a significantly higher basal firing rate in 2.5 mmol l-1 glucose than DM-VMN GE/PER channels. No significant difference in the distribution of GI/PED channels was observed between the VMN subregions. The results of the present study demonstrate the utility of the pMEA approach for evaluating glucose responsivity across the mouse VMN. pMEA studies could be used to refine our understanding of other neuroendocrine systems by examining population level changes in electrical activity across brain nuclei, thus providing key functional neuroanatomical information to complement and inform the design of single-cell neurophysiological studies.

Protein kinase inhibitors infused intraventricularly or into the ventromedial hypothalamus block short latency facilitation of lordosis by oestradiol.

An injection of unesterified oestradiol (E2 ) facilitates receptive behaviour in E2 benzoate (EB)-primed, ovariectomised female rats when it is administered i.c.v. or systemically. The present study tested the hypothesis that inhibitors of protein kinase A (PKA), protein kinase G (PKG) or the Src/mitogen-activated protein kinase (MAPK) complex interfere with E2 facilitation of receptive behaviour. In Experiment 1, lordosis induced by i.c.v. infusion of E2 was significantly reduced by i.c.v. administration of Rp-cAMPS, a PKA inhibitor, KT5823, a PKG inhibitor, and PP2 and PD98059, Src and MAPK inhibitors, respectively, between 30 and 240 minutes after infusion. In Experiment 2, we determined whether the ventromedial hypothalamus (VMH) is one of the neural sites at which those intracellular pathways participate in lordosis behaviour induced by E2 . Administration of each of the four protein kinase inhibitors into the VMH blocked facilitation of lordosis induced by infusion of E2 also into the VMH. These data support the hypothesis that activation of several protein kinase pathways is involved in the facilitation of lordosis by E2 in EB-primed rats.