Hypothalamic control of innate social behaviors

The endocannabinoid and paracannabinoid systems in natural reward processes: possible pharmacological targets?

Natural rewards such as food, mating, and social interaction are essential for survival and species preservation, and their regulation involves a complex interplay of motivational, cognitive, and emotional processes. Over the past two decades, increasing attention has been directed toward the endocannabinoid system and its paracannabinoid counterpart as key modulators of these behaviors. This review aims to provide an integrated overview of the roles played by the endocannabinoid and paracannabinoid systems in regulating natural reward-driven behaviors, focusing on feeding, reproductive behavior, and social interaction. We highlight how the endocannabinoid system - mainly through CB1 receptor signaling - modulates central and peripheral circuits involved in energy homeostasis, reward processing, and emotional regulation. In parallel, we explore the role of paracannabinoids, such as oleoylethanolamide (OEA), palmitoylethanolamide (PEA), and stearoylethanolamide (SEA), which act primarily via non-cannabinoid receptors and contribute to the regulation of appetite, sexual motivation, and social behavior. Special attention is given to the relevance of these systems in the pathophysiology of obesity, eating disorders, sexual dysfunctions, and social impairments, as well as their potential as pharmacological targets. Overall, the evidence discussed supports a broader conceptualization of endocannabinoid and paracannabinoid signaling as pivotal regulators of natural rewards and opens new avenues for the development of targeted interventions for motivational and reward-related disorders.

Repeated non-contact exposure to pups inhibits infanticidal and facilitates paternal behavior in virgin adult male mice (C57BL6)

Pup-naïve virgin adult male C57BL6 mice are mainly infanticidal when exposed to pups for the first time. The processes underlying pup-directed aggression and the transition toward parental care are poorly understood. Social isolation has been shown to inhibit infanticidal behavior in some strain of mice. However, it is unclear if highly infanticidal male CB57BL6 mice can sensitize after repeated exposures to pups. The aim of this study was to determine whether repeated non-contact exposure to pups (to prevent immediate attack), with or without movement restriction and social isolation, can inhibit infanticidal behavior in male mice. We also investigated whether pup-directed aggression was associated with male-male aggression in a resident-intruder test. We found that repeated non-contact exposure to pups, in socially isolated males or in males with movement restraint, significantly reduced the incidence of aggression towards pups and increased the incidence of parental behavior. Social isolation or movement restraint alone had no significant effect. Finally, the frequency of pup-directed aggression was not associated with the levels of male-male aggression. This study shows that the experience of being exposed to newborns without contact with them can inhibit the highly driven impulsive-like attacking behavior towards pups and facilitate parental behavior. Our results suggest that aggressive behavior towards pups can be blocked in naïve male mice and that this behavior differs from male-male aggression.

From social effort to social behavior: An integrated neural model for social motivation

As humans rely on social groups for survival, social motivation is central to behavior and well-being. Here we define social motivation as the effort that initiates and directs behavior towards social outcomes, with the goal of satisfying our fundamental need for connection. We propose an integrated framework of social motivation which emphasizes the maintenance of optimal connection levels through effort exertion, regulating social approach and avoidance, which allow interpersonal synchrony. Together, these behaviors serve as basic building blocks of social behavior, and give rise to behaviors critical for collective living such as cooperation and empathy. We describe a neural model according to which social connection levels are monitored by the hypothalamus, while the anterior cingulate cortex and anterior insula respond to detected social deficiency. As adjustment is required, the social effort system - comprised of the thalamus and striatum - is activated. This system directs neural networks that permit interpersonal synchrony or, conversely, desynchronization, aiming to restore and maintain optimal connection by preventing isolation on the one hand, and exaggerated social closeness on the other hand. The proposed framework offers insights into disorders characterized by aberrant social motivation, potentially identifying neural dysfunctions that may inform novel interventions.

Hormonal regulation of behavioral and emotional persistence: Novel insights from a systems-level approach to neuroendocrinology

Gonadal sex steroid hormones regulate internal states, social drive, perception of external cues, and learning and memory. Fluctuating hormones influence mood and emotional states, enabling flexibility in instinctive behaviors and cognitive decisions. Conversely, elevated hormone levels help sustain emotional states and behavioral choices, ensuring the precise execution of costly social behaviors within optimal time windows to maximize reproductive success. While decades of work have shed light on the cellular and molecular mechanisms by which sex hormones alter neural excitability and circuit architecture, recent work has begun to tie many of these changes to principles of computation using the tools of systems neuroscience. Here, we will outline the mechanisms by which sex steroid hormones alter neural functioning at the molecular and cellular level and highlight recent work that points towards changes in specific computational functions, including the generation and maintenance of neural and behavioral persistence.

Estradiol Reverses Ovariectomy-Induced Disruption of Hypothalamic Gene Expression and Behavior via Modulation of Gonadotropin Releasing Hormone and Calcium Signaling Pathways

Estrogen plays a crucial role in regulating reproductive and neuroendocrine functions, yet the molecular mechanisms underlying its effects on the hypothalamus remain incompletely understood. This study investigates the transcriptional and behavioral changes induced by ovariectomy (OVX) and estradiol (E2) supplementation in female C57BL/6J mice. RNA sequencing was performed to identify differentially expressed genes (DEGs) across control (CK), E2, OVX, and OVX+E2 groups, followed by functional enrichment and pathway analyses. Behavioral assessments, including open field, Y-maze, and elevated plus maze tests, were conducted to evaluate anxiety-like and cognitive behaviors. Results revealed significant alterations in GnRH signaling, neurotransmission, and inflammatory pathways, with key genes such as Elk1, Prkcb, and Camk2a differentially expressed in response to estrogen modulation. OVX-induced neuroendocrine disruptions were partially reversed by E2 treatment, as evidenced by transcriptomic and behavioral outcomes. Pearson correlation analysis further linked gene expression patterns with phenotypic traits, providing insights into estrogen's regulatory mechanisms in the hypothalamus. These findings enhance our understanding of estrogen-mediated neuroendocrine regulation and may have implications for hormone replacement therapies in postmenopausal disorders.

Neural basis of aggressive behavior toward newborns in Mice: Advances and future Challenges

Infanticidal or pup-directed aggressive behavior is present in most species, including humans. It occurs in both reproductive and non-reproductive contexts and its incidence and biological basis may vary among species, strains, sex, and individual experiences. This review has two objectives: 1) to describe the most likely neural circuit that mediates aggressive behavior towards pups in mice, including hormonal, neuroendocrine and neurochemical changes that may increase the probability of attacking pups; and 2) to discuss whether aggressive behavior toward pups in mice is rewarding, an impulsive or predatory response, or a form of maltreatment or adaptive behavior. We propose a neural model to explain aggressive behavior towards pups and discuss evidence suggesting that infanticidal and pup-directed aggressive behavior, although hard-wired in the brain, can be blocked or inhibited by changing the experiences of the subject prior to the access to pups.

Advancements in autism spectrum disorder research --from mechanisms to interventions

This review summarizes recent advancements in the research of autism spectrum disorders (ASD), emphasizing genetic underpinnings and their implications for neurodevelopment and cognitive functions. It explores both syndromic and nonsyndromic ASD, highlighting the discovery of critical ASD-related genes and their mechanistic roles as revealed by studies using genetically engineered mouse and non-human primate models. While these models have shed light on the potential of synaptic dysfunction to disrupt brain development, they also underscore the challenges of replicating complex cognitive dysfunctions observed in ASD. Recent successes in gene therapy, particularly through innovative approaches like gene replacement and base editing, offer promising pathways for addressing genetic anomalies in ASD. These therapeutic strategies, underscored by clinical trials and cutting-edge genetic manipulation techniques, pave the way for potential interventions that could profoundly impact ASD management and treatment.

Integrating innate and learned behavior through brain circuits

Understanding how innate predispositions and learned experiences interact to shape behavior is a central question in systems neuroscience. Traditionally, innate behaviors, that is, those present without prior learning and governed by evolutionarily conserved neural circuits, have been studied separately from learned behaviors, which depend on experience and neural plasticity. This division has led to a compartmentalized view of behavior and neural circuit organization. Increasing evidence suggests that innate and learned behaviors are not independent, but rather deeply intertwined, with plasticity evident even in circuits classically considered 'innate'. In this opinion, we highlight examples across species that illustrate the dynamic interaction between these behavioral domains and discuss the implications for unifying theoretical and empirical frameworks. We argue that a more integrative approach, namely one that acknowledges the reciprocal influences of innate and learned processes, is essential for advancing our understanding of how neuronal activity drives complex behaviors.

Brain circuits that regulate social behavior

Social interactions are essential for the survival of individuals and the reproduction of populations. Social stressors, such as social defeat and isolation, can lead to emotional disorders and cognitive impairments. Furthermore, dysfunctional social behaviors are hallmark symptoms of various neuropsychiatric disorders, including autism spectrum disorder (ASD) and post-traumatic stress disorder (PTSD). Consequently, understanding the neural circuit mechanisms underlying social behaviors has become a major focus in neuroscience. Social behaviors, which encompass a wide range of expressions and phases, are regulated by complex neural networks. In this review, we summarize recent progress in identifying the circuits involved in different types of social behaviors, including general social investigation, social preference, mating, aggression, parenting, prosocial behaviors, and dominance behaviors. We also outline the circuit mechanisms associated with social deficits in neuropsychiatric disorders, such as ASD, schizophrenia, and PTSD. Given the pivotal role of rodents in social behavior research, our review primarily focuses on neural circuits in these animals. Finally, we propose future research directions, including the development of specific behavioral paradigms, the identification of circuits involved in motor output, the integration of activity, transcriptome, and connectome data, the multifunctional roles of neurons with multiple targets, and the interactions among multiple brain regions.

Cellular evolution of the hypothalamic preoptic area of behaviorally divergent deer mice

Genetic variation is known to contribute to the variation of animal social behavior, but the molecular mechanisms that lead to behavioral differences are still not fully understood. Here, we investigate the cellular evolution of the hypothalamic preoptic area (POA), a brain region that plays a critical role in social behavior, across two sister species of deer mice (Peromyscus maniculatus and P. polionotus) with divergent social systems. These two species exhibit large differences in mating and parental care behavior across species and sex. Using single-nucleus RNA-sequencing, we build a cellular atlas of the POA for males and females of both Peromyscus species. We identify four cell types that are differentially abundant across species, two of which may account for species differences in parental care behavior based on known functions of these cell types. Our data further implicate two sex-biased cell types to be important for the evolution of sex-specific behavior. Finally, we show a remarkable reduction of sex-biased gene expression in P. polionotus, a monogamous species that also exhibits reduced sexual dimorphism in parental care behavior. Our POA atlas is a powerful resource to investigate how molecular neuronal traits may be evolving to give rise to innate differences in social behavior across animal species.

Integrating the COM-B model into behavioral neuroscience: A framework for understanding animal behavior

In light of the intricate nature of animal behavior regulation, a theoretical model is proposed, grounded in the COM-B (Capability, Opportunity, Motivation - Behavior) framework, which has gained considerable traction in the domain of human behavioral intervention. When extending the COM-B model to behavioral neuroscience, we first discuss the utility of the model in animal research, particularly its capacity to integrate environmental and social factors, and enhance cross-species comparisons, including animal-to-human translations and evolutionary considerations. The subsequent discussion then summarizes the advantages of utilizing the COM-B model in neuroscience are summarized, including the facilitation of a systems-level understanding of behavior and the establishment of a link between neural mechanisms and specific behavioral components. The experimental design for the application of the COM-B model in neuroscience is proposed to elucidate the brain regulatory processes that govern behavior. Finally, three specific examples are provided to illustrate the theoretical considerations, namely feeding and social behavior, and the role of neuromodulators in the control of behavior.

A review of the effects of different types of social behaviors on the recruitment of neuropeptides and neurotransmitters in the nucleus accumbens

There is a lack of understanding of the neural mechanisms regulating the rewarding effects of social interactions. A significant contributor to this lack of clarity is the diversity of social behaviors and animal models utilized to investigate mechanisms. Other sources of the lack of clarity are the diversity of brain regions that can regulate social reward and the diversity of signaling pathways that regulate reward. To provide some clarity into the mechanisms of social reward, this review focused on the brain region most implicated in reward for multiple stimuli, the nucleus accumbens, and surveyed (systematically reviewed) studies that investigated the relationship between social interaction and five signaling systems implicated in the regulation of reward and social behavior: oxytocin, vasopressin, serotonin, opioids and endocannabinoids. Moreover, all of these studies were organized by the type of social behavior studied: affiliative interactions, play behavior, aggression, social defeat, sex behavior, pair-bonding, parental behavior and social isolation. From this survey and organization, this review concludes that oxytocin, endocannabinoids and mu-opioid receptors in the nucleus accumbens positively regulate the rewarding social behaviors, and kappa-opioid receptors negatively regulate the rewarding social behaviors. The opposite profile is observed for these signaling systems for the aversive social behaviors. More studies are needed to investigate the directional role of the serotonin system in the nucleus accumbens in the regulation of many types of social behaviors, and vasopressin likely does not act in the nucleus accumbens in the regulation of the valence of social behaviors. Many of these different signaling systems are also interdependent of one another in the regulation of different types of social behaviors. Finally, the interaction of these signaling systems with dopamine in the nucleus accumbens is briefly discussed.

CART neurons in the hypothalamic ventral premammillary nucleus (PMv) in rats mediate maternal, but not inter-male aggression

Compared to males, aggression is less frequently noticed in females. Fierce maternal-aggression to thwart the attack/threat of male-conspecific/intruder is transiently expressed as she defends her pups. The odor cues emanated by the intruder provoke aggressive behavior by robustly activating the ventral-premammillary nucleus (PMv) in the hypothalamic-attack area (HAA). But, how PMv activation triggers aggression is unclear. In view of neuropeptide CART's potential to reconfigure neural circuits for behavioral demands, occurrence throughout aggression-circuitry, and abundance particularly in PMv, we test the role of PMvCART in maternal and inter-male aggression in the rats. Males/dams actively attacked the intruder; virgin-females did not. The dams/males without intruder showed isolated cFos-cells in PMv, but intruder's presence triggered cFos-activation in different PMv-subdivisions in dams/males. Compared to dams without intruder, confrontation with intruder robustly activated PMvCART-neurons, augmented CART-ir in ventral-PMv and cart-mRNA in PMv-containing tissues in dams. Conversely, in males, intruder's presence activated lateral-PMv CART neurons, but CART-levels remained unaltered. Intra-PMv CART-siRNA administration suppressed maternal-aggression but male-aggression was unaffected. Since PMv is strongly connected with ventrolateral-ventromedial hypothalamus (VMHvl) and medial-preoptic nucleus (MPN), we test whether CART-signalling to these nuclei triggers maternal-aggression. While VMHvl showed stronger CARTergic-axonal input than MPN, immunoneutralization of CART in VMHvl but not MPN, blocked maternal-aggression. CART may drive the circuit beyond HAA since VMHvl neurons contacted by CART-axons project to periaqueductal-gray. We identify engagement of vPMv and lPMv during maternal and inter-male aggression, respectively, and CART as a key mediator in PMv-VMHvl-pathway to express maternal-aggression in rats.Significance statement Pregnant/lactating rat transiently become fiercely aggressive to protect her pups when challenged by an intruder. The neural mechanism underlying this transitory expression of aggressive behavior is not clear. We identify the role of neuropeptide CART-containing neurons in the hypothalamic premammillary nucleus (PMv) in dams that gives her the behavioral flexibility to display maternal-aggression. A subset of PMvCART neurons in dams shows dramatic activation when provoked by an intruder while silencing of these neurons suppressed maternal- but not male-male aggression. Further, CART signals the ventrolateral part of the ventromedial hypothalamus to trigger aggression in dams. The study shows CART as a novel messenger in aggression circuitry and PMvCART a key regulator of maternal-aggression.

Segregated input to thalamic areas that project differently to core and shell auditory cortical fields

Perception of the environment is multimodal in nature, with sensory systems intricately interconnected. The ability to integrate multimodal sensations while preserving the distinct characteristics of each sensory modality is crucial, and the underlying mechanisms of the organization that facilitate this process require further elucidation. In the auditory system, although the concept of core and shell pathways is well established, the brain-wide input/output relationships of thalamic regions projecting to auditory-responsive cortical areas remain insufficiently studied, particularly in relation to non-auditory structures. In this study, we utilized functional imaging and viral tracing techniques to map the brain-wide connections of core and shell pathways. We identified three distinct shell pathways, in addition to a core pathway, each exhibiting unique associations with non-auditory structures involved in behavior, emotion, and other functions. This architecture suggests that these pathways contribute differentially to various aspects of multimodal sensory integration.

Low-Frequency Stimulation at the Ventromedial Hypothalamus Exhibits Broad-Spectrum Efficacy Across Models of Epilepsy

AIMS

The limited efficacy and very restricted antiseizure range of current deep brain stimulation (DBS) targets highlight the need to find an optimal target for managing various seizure types. Here, we aimed to investigate the efficacy of DBS on the ventromedial hypothalamus (VMH) in the different types of experimental epileptic seizures.

METHODS

The efficacy of DBS was examined in various epileptic seizure models, and the potential mechanisms were investigated by using in vivo calcium signal recording and optogenetics.

RESULTS

The c-fos expression was significantly increased in the glutamatergic neurons of VMH (VMHglu) following seizures. Then, 1-Hz low-frequency stimulation (LFS) at the VMH successfully attenuated the seizure severities across models of epilepsy, including the maximal electroshock, the pentylenetetrazol, the absence seizure, the cortical or hippocampal kainic acid-induced acute seizure, and the hippocampal-kindling models. The in vivo calcium imaging recordings revealed that LFS could inhibit the activities of the VMHglu. Optogenetic inhibition of VMHglu mirrored LFS's antiseizure impact. Further anterograde viral tracing confirmed the extensive distributed projections of VMHglu, which may compose the circuitry basis of the broad-spectral efficacy of LFS.

CONCLUSION

These findings demonstrate that VMH-LFS is a broad-spectrum treatment approach for different seizure types by decreasing VMHglu activity.

Hypothalamic Vasopressin Neurons Enable Maternal Thermoregulatory Behaviors

Newborns of many mammalian species are partial poikilotherms and require adult thermoregulatory care for survival. In mice, pup survival in cold and cool ambient temperature depends on the ability of adult caregivers to huddle pups and bring them into a high-quality nest. It is therefore essential that adult mice adjust parental care as a function of changes in ambient temperature. Here, we investigated how mouse maternal care adapts to a range of temperatures, from cold to warm. We show that changes in ambient temperature affect several individual and co-parenting maternal behaviors in both dams and virgin female mice, and modulate activity of vasopressin neurons. Furthermore, we establish that the effects of ambient temperature on both maternal care and the activity of vasopressin neurons depend in part on thermosensation, specifically on the TRPM8 sensor. Using trans-synaptic anterograde tracing and whole-brain activity mapping, we find that vasopressin neurons from the paraventricular hypothalamic nucleus connect synaptically with temperature-responsive brain structures implicated in maternal care. We then show that optogenetic activation of vasopressin projections to the central amygdala, a structure activated by cold ambient temperature, recapitulates the effects of cold on co-parenting behaviors. Our data provide a biological mechanism for maternal thermoregulatory behavior in mice with translational relevance to the reported association between ecosystem temperature fluctuations and variations in human child neglect cases.

Cellular evolution of the hypothalamic preoptic area of behaviorally divergent deer mice

Genetic variation is known to contribute to the variation of animal social behavior, but the molecular mechanisms that lead to behavioral differences are still not fully understood. Here, we investigate the cellular evolution of the hypothalamic preoptic area (POA), a brain region that plays a critical role in social behavior, across two sister species of deer mice (Peromyscus maniculatus and P. polionotus) with divergent social systems. These two species exhibit large differences in mating and parental care behavior across species and sex. Using single-nucleus RNA-sequencing, we build a cellular atlas of the POA for males and females of both Peromyscus species. We identify four cell types that are differentially abundant across species, two of which may account for species differences in parental care behavior based on known functions of these cell types. Our data further implicate two sex-biased cell types to be important for the evolution of sex-specific behavior. Finally, we show a remarkable reduction of sex-biased gene expression in P. polionotus, a monogamous species that also exhibits reduced sexual dimorphism in parental care behavior. Our POA atlas is a powerful resource to investigate how molecular neuronal traits may be evolving to give rise to innate differences in social behavior across animal species.

Nesfatin-1 Neurons in the Ventral Premammillary Nucleus Integrate Metabolic and Reproductive Signals in Male Rats

The ability to reproduce depends on metabolic status. In rodents, the ventral premammillary nucleus (PMv) integrates metabolic and reproductive signals. While leptin (adiposity-related) signaling in the PMv is critical for female fertility, male reproductive functions are strongly influenced by glucose homeostasis. The anorexigenic peptide nesfatin-1 is a leptin-independent central regulator of blood glucose. Therefore, its integrative role in male rats can be assumed. To investigate this, we mapped the distribution of nesfatin-1 mRNA- and protein-producing cells in the PMv during postnatal development via in situ hybridization and immunohistochemistry, respectively. Fos-nesfatin-1, double immunostaining was used to determine the combined effect of heterosexual pheromone challenge and insulin-induced hypoglycemia on neuronal activation in adults. We found that ~75% of the pheromone-activated neurons were nesfatin-1 cells. Hypoglycemia reduced pheromone-induced cell activation, particularly in nesfatin-1 neurons. Immuno-electron microscopy revealed innervation of PMv nesfatin-1 neurons by urocortin3-immunoreactive terminals, reportedly originating from the medial amygdala. Nesfatin-1 immunopositive neurons expressed GPR10 mRNA, a receptor associated with metabolic signaling, but did not respond with accumulation of phosphorylated STAT3 immunopositivity, a marker of leptin receptor signaling, in response to intracerebroventricular leptin treatment. Our results suggest that PMv nesfatin-1 neurons are primarily responsible for integrating reproductive and metabolic signaling in male rats.

The role of the prefrontal cortex in modulating aggression in humans and rodents

Accumulating evidence suggests that the prefrontal cortex (PFC) plays an important role in aggression. However, the findings regarding the key neural mechanisms and molecular pathways underlying the modulation of aggression by the PFC are relatively scattered, with many inconsistencies and areas that would benefit from exploration. Here, we highlight the relationship between the PFC and aggression in humans and rodents and describe the anatomy and function of the human PFC, along with homologous regions in rodents. At the molecular level, we detail how the major neuromodulators of the PFC impact aggression. At the circuit level, this review provides an overview of known and potential subcortical projections that regulate aggression in rodents. Finally, at the disease level, we review the correlation between PFC alterations and heightened aggression in specific human psychiatric disorders. Our review provides a framework for PFC modulation of aggression, resolves several intriguing paradoxes from previous studies, and illuminates new avenues for further study.

The lateral thalamus: a bridge between multisensory processing and naturalistic behaviors

The lateral thalamus (LT) receives input from primary sensory nuclei and responds to multimodal stimuli. The LT is also involved in regulating innate and social behaviors through its projections to cortical and limbic networks. However, the importance of multisensory processing within the LT in modulating behavioral output has not been explicitly addressed. Here, we discuss recent findings primarily from rodent studies that extend the classical view of the LT as a passive relay, by underscoring its involvement in associating multimodal features and encoding the salience, valence, and social relevance of sensory signals. We propose that the primary function of the LT is to integrate sensory and non-sensory aspects of multisensory input to gate naturalistic behaviors.

Chemogenetic Modulation of Preoptic Gabre Neurons Decreases Body Temperature and Heart Rate

The preoptic area of the hypothalamus is critical for regulation of brain-body interaction, including circuits that control vital signs such as body temperature and heart rate. The preoptic area contains approximately 70 molecularly distinct cell types. The Gabre gene is expressed in a subset of preoptic area cell types. It encodes the GABA receptor ε-subunit, which is thought to confer resistance to anesthetics at the molecular level, but the function of Gabre cells in the brain remains largely unknown. We generated and have extensively characterized a Gabre-cre knock-in mouse line and used chemogenetic tools to interrogate the function of Gabre cells in the preoptic area. Comparison with macaque GABRE expression revealed the conserved character of Gabre cells in the preoptic area. In awake mice, we found that chemogenetic activation of Gabre neurons in the preoptic area reduced body temperature, whereas chemogenetic inhibition had no effect. Furthermore, chemogenetic inhibition of Gabre neurons in the preoptic area decreased the heart rate, whereas chemogenetic activation had no effect under isoflurane anesthesia. These findings suggest an important role of preoptic Gabre neurons in maintaining vital signs such as body temperature and heart rate during wakefulness and under anesthesia.

Interconnected neural circuits mediating social reward

Across species, social behaviors are shaped and maintained through positive reinforcement of affiliative social interactions. As with nonsocial rewards, the reinforcing properties of social interactions have been shown to involve interplay between various brain regions and the mesolimbic reward system. In this review, we summarize findings from rodent research on the neural circuits that encode and mediate different components of social reward-seeking behavior. We explore methods to parse and study social reward-related behaviors using available behavioral paradigms. We also compare the neural mechanisms that support social versus nonsocial reward-seeking. Finally, we discuss how internal state and neuromodulatory systems affect reward-seeking behavior and the neural circuits that underlie social reward.

A novel quadrant spatial assay reveals environmental preference in mouse spontaneous and parental behaviors

Environmental factors have well-documented impacts on brain development and mental health. Therefore, it is crucial to employ a reliable assay system to assess the spatial preference of model animals. In this study, we introduced an unbiased quadrant chamber assay system and discovered that parental pup-gathering behavior takes place in a very efficient manner. Furthermore, we found that test mice exhibited preferences for specific environments in both spontaneous and parental pup-gathering behavior contexts. Notably, the spatial preferences of autism spectrum disorder model animals were initially suppressed but later equalized during the spontaneous behavior assay, accompanied by increased time spent in the preferred chamber. In conclusion, our novel quadrant chamber assay system provides an ideal platform for investigating the spatial preference of mice, offering potential applications in studying environmental impacts and exploring neurodevelopmental and psychiatric disorder models.

The multi-stage plasticity in the aggression circuit underlying the winner effect

Winning increases the readiness to attack and the probability of winning, a widespread phenomenon known as the "winner effect." Here, we reveal a transition from target-specific to generalized aggression enhancement over 10 days of winning in male mice. This behavioral change is supported by three causally linked plasticity events in the ventrolateral part of the ventromedial hypothalamus (VMHvl), a critical node for aggression. Over 10 days of winning, VMHvl cells experience monotonic potentiation of long-range excitatory inputs, transient local connectivity strengthening, and a delayed excitability increase. Optogenetically coactivating the posterior amygdala (PA) terminals and VMHvl cells potentiates the PA-VMHvl pathway and triggers the same cascade of plasticity events observed during repeated winning. Optogenetically blocking PA-VMHvl synaptic potentiation eliminates all winning-induced plasticity. These results reveal the complex Hebbian synaptic and excitability plasticity in the aggression circuit during winning, ultimately leading to increased "aggressiveness" in repeated winners.

Molecular and functional mapping of the neuroendocrine hypothalamus: a new era begins

BACKGROUND

Recent advances in neuroscience tools for single-cell molecular profiling of brain neurons have revealed an enormous spectrum of neuronal subpopulations within the neuroendocrine hypothalamus, highlighting the remarkable molecular and cellular heterogeneity of this brain area.

RATIONALE

Neuronal diversity in the hypothalamus reflects the high functional plasticity of this brain area, where multiple neuronal populations flexibly integrate a variety of physiological outputs, including energy balance, stress and fertility, through crosstalk mechanisms with peripheral hormones. Intrinsic functional heterogeneity is also observed within classically 'defined' subpopulations of neuroendocrine neurons, including subtypes with distinct neurochemical signatures, spatial organisation and responsiveness to hormonal cues.

AIM

The aim of this review is to critically evaluate past and current research on the functional diversity of hypothalamic neuroendocrine neurons and their plasticity. It focuses on how this neuronal plasticity in this brain area relates to metabolic control, feeding regulation and interactions with stress and fertility-related neural circuits.

CONCLUSION

Our analysis provides an original framework for improving our understanding of the hypothalamic regulation of hormone function and the development of neuroendocrine diseases.

A mindful approach to complications: Brief review of the literature and practical guide for the surgeon

Patient complications and adverse outcomes are inherent to surgical practice and training. In addition to the impact on patients, there are profound and well-documented impacts of complications on surgeons, surgical trainees, and surgical teams. This manuscript reviews the literature regarding mindfulness-based practices and the associated mitigation of the adverse impact of complications. These mindfulness-based practices prepare surgeons for complications by improving mental and cognitive resilience facilitating more effective management of complications that avoids undue psychological and emotional stress. Practical recommendations are provided for the practicing surgeon from providers experienced in mindfulness-based training and preparation.

Causal evidence of a line attractor encoding an affective state

Continuous attractors are an emergent property of neural population dynamics that have been hypothesized to encode continuous variables such as head direction and eye position1-4. In mammals, direct evidence of neural implementation of a continuous attractor has been hindered by the challenge of targeting perturbations to specific neurons within contributing ensembles2,3. Dynamical systems modelling has revealed that neurons in the hypothalamus exhibit approximate line-attractor dynamics in male mice during aggressive encounters5. We have previously hypothesized that these dynamics may encode the variable intensity and persistence of an aggressive internal state. Here we report that these neurons also showed line-attractor dynamics in head-fixed mice observing aggression6. This allowed us to identify and manipulate line-attractor-contributing neurons using two-photon calcium imaging and holographic optogenetic perturbations. On-manifold perturbations yielded integration of optogenetic stimulation pulses and persistent activity that drove the system along the line attractor, while transient off-manifold perturbations were followed by rapid relaxation back into the attractor. Furthermore, single-cell stimulation and imaging revealed selective functional connectivity among attractor-contributing neurons. Notably, individual differences among mice in line-attractor stability were correlated with the degree of functional connectivity among attractor-contributing neurons. Mechanistic recurrent neural network modelling indicated that dense subnetwork connectivity and slow neurotransmission7 best recapitulate our empirical findings. Our work bridges circuit and manifold levels3, providing causal evidence of continuous attractor dynamics encoding an affective internal state in the mammalian hypothalamus.

The multi-stage plasticity in the aggression circuit underlying the winner effect

Winning increases the readiness to attack and the probability of winning, a widespread phenomenon known as the "winner effect". Here, we reveal a transition from target-specific to generalized aggression enhancement over 10 days of winning in male mice, which is supported by three stages of plasticity in the ventrolateral part of the ventromedial hypothalamus (VMHvl), a critical node for aggression. Over 10-day winning, VMHvl cells experience monotonic potentiation of long-range excitatory inputs, a transient local connectivity strengthening, and a delayed excitability increase. These plasticity events are causally linked. Optogenetically coactivating the posterior amygdala (PA) terminals and VMHvl cells potentiates the PA-VMHvl pathway and triggers the cascade of plasticity events as those during repeated winning. Optogenetically blocking PA-VMHvl synaptic potentiation eliminates all winning-induced plasticity. These results reveal the complex Hebbian synaptic and excitability plasticity in the aggression circuit during winning that ultimately leads to an increase in "aggressiveness" in repeated winners.

Aggression Unleashed: Neural Circuits from Scent to Brain

Aggression is a fundamental behavior with essential roles in dominance assertion, resource acquisition, and self-defense across the animal kingdom. However, dysregulation of the aggression circuitry can have severe consequences in humans, leading to economic, emotional, and societal burdens. Previous inconsistencies in aggression research have been due to limitations in techniques for studying these neurons at a high spatial resolution, resulting in an incomplete understanding of the neural mechanisms underlying aggression. Recent advancements in optogenetics, pharmacogenetics, single-cell RNA sequencing, and in vivo electrophysiology have provided new insights into this complex circuitry. This review aims to explore the aggression-provoking stimuli and their detection in rodents, particularly through the olfactory systems. Additionally, we will examine the core regions associated with aggression, their interactions, and their connection with the prefrontal cortex. We will also discuss the significance of top-down cognitive control systems in regulating atypical expressions of aggressive behavior. While the focus will primarily be on rodent circuitry, we will briefly touch upon the modulation of aggression in humans through the prefrontal cortex and discuss emerging therapeutic interventions that may benefit individuals with aggression disorders. This comprehensive understanding of the neural substrates of aggression will pave the way for the development of novel therapeutic strategies and clinical interventions. This approach contrasts with the broader perspective on neural mechanisms of aggression across species, aiming for a more focused analysis of specific pathways and their implications for therapeutic interventions.

Medial preoptic circuits governing instinctive social behaviors

The medial preoptic area (MPOA) has long been implicated in maternal and male sexual behavior. Modern neuroscience methods have begun to reveal the cellular networks responsible, while also implicating the MPOA in other social behaviors, affiliative social touch, and aggression. The social interactions rely on input from conspecifics whose most important modalities in rodents are olfaction and somatosensation. These inputs bypass the cerebral cortex to reach the MPOA to influence the social function. Hormonal inputs also directly act on MPOA neurons. In turn, the MPOA controls social responses via various projections for reward and motor output. The MPOA thus emerges as one of the major brain centers for instinctive social behavior. While key elements of MPOA circuits have been identified, a synthesis of these new data is now provided for further studies to reveal the mechanisms by which the area controls social interactions.

Investigating social communication in mice: A two-intruders test approach

Understanding the complex dynamics of social communication behaviors, such as exploration, communication, courtship, mating, and aggression in animal models, is crucial to reveal key neural and hormonal mechanisms underlying these behaviors. The two-intruders test is designed to investigate residents' behavior toward both male and female intruders within the home cage of the test male. During this test imitating natural conditions, several aspects of social interaction were investigated: Exploration, courtship, mating, and aggressive behavior. As mating and aggression involve overlapping neural circuits, the behavioral setup testing both behaviors is best at reflecting their competitive nature. Our findings demonstrate that resident male mice exhibit strong preference to communicate with a female intruder, which correlates with baseline testosterone levels of test males. Relevant female preference in the two-intruders test was also found in BALB/c males. Behavioral breakdown revealed the anogenital sniffing as a key behavioral feature that discriminates resident male behavior toward intruders of different sex. Furthermore, resident male interaction with female intruder was accompanied by neuronal activation in the ventromedial hypothalamus. We demonstrate that odor recognition underlies preference toward females in male residents, as experimental anosmia reduced communication with a female intruder. We conclude the two-intruders test setup to be a useful tool to study the neurological basis of social communication in animal models, which provides detailed analysis of various aspects of the laboratory animals' social behavior in the most natural conditions.

Identifying behavioral links to neural dynamics of multifiber photometry recordings in a mouse social behavior network

Objective.Distributed hypothalamic-midbrain neural circuits help orchestrate complex behavioral responses during social interactions. Given rapid advances in optical imaging, it is a fundamental question how population-averaged neural activity measured by multi-fiber photometry (MFP) for calcium fluorescence signals correlates with social behaviors is a fundamental question. This paper aims to investigate the correspondence between MFP data and social behaviors.Approach:We propose a state-space analysis framework to characterize mouse MFP data based on dynamic latent variable models, which include a continuous-state linear dynamical system and a discrete-state hidden semi-Markov model. We validate these models on extensive MFP recordings during aggressive and mating behaviors in male-male and male-female interactions, respectively.Main results:Our results show that these models are capable of capturing both temporal behavioral structure and associated neural states, and produce interpretable latent states. Our approach is also validated in computer simulations in the presence of known ground truth.Significance:Overall, these analysis approaches provide a state-space framework to examine neural dynamics underlying social behaviors and reveals mechanistic insights into the relevant networks.

Reproductive function and behaviors: an update on the role of neural estrogen receptors alpha and beta

Infertility is becoming a major public health problem, with increasing frequency due to medical, environmental and societal causes. The increasingly late age of childbearing, growing exposure to endocrine disruptors and other reprotoxic products, and increasing number of medical reproductive dysfunctions (endometriosis, polycystic ovary syndrome, etc.) are among the most common causes. Fertility relies on fine-tuned control of both neuroendocrine function and reproductive behaviors, those are critically regulated by sex steroid hormones. Testosterone and estradiol exert organizational and activational effects throughout life to establish and activate the neural circuits underlying reproductive function. This regulation is mediated through estrogen receptors (ERs) and androgen receptor (AR). Estradiol acts mainly via nuclear estrogen receptors ERα and ERβ. The aim of this review is to summarize the genetic studies that have been undertaken to comprehend the specific contribution of ERα and ERβ in the neural circuits underlying the regulation of the hypothalamic-pituitary-gonadal axis and the expression of reproductive behaviors, including sexual and parental behavior. Particular emphasis will be placed on the neural role of these receptors and the underlying sex differences.

Role of neuroestrogens in the regulation of social behaviors - From social recognition to mating

In this mini-review, we summarize the brain distribution of aromatase, the enzyme catalyzing the synthesis of estrogens from androgens, and the mechanisms responsible for regulating estrogen production within the brain. Understanding this local synthesis of estrogens by neurons is pivotal as it profoundly influences various facets of social behavior. Neuroestrogen action spans from the initial processing of socially pertinent sensory cues to integrating this information with an individual's internal state, ultimately resulting in the manifestation of either pro-affiliative or - aggressive behaviors. We focus here in particular on aggressive and sexual behavior as the result of correct individual recognition of intruders and potential mates. The data summarized in this review clearly point out the crucial role of locally synthesized estrogens in facilitating rapid adaptation to the social environment in rodents and birds of both sexes. These observations not only shed light on the evolutionary significance but also indicate the potential implications of these findings in the realm of human health, suggesting a compelling avenue for further investigation.

Intrinsic Dynamics and Neural Implementation of a Hypothalamic Line Attractor Encoding an Internal Behavioral State

Line attractors are emergent population dynamics hypothesized to encode continuous variables such as head direction and internal states. In mammals, direct evidence of neural implementation of a line attractor has been hindered by the challenge of targeting perturbations to specific neurons within contributing ensembles. Estrogen receptor type 1 (Esr1)-expressing neurons in the ventrolateral subdivision of the ventromedial hypothalamus (VMHvl) show line attractor dynamics in male mice during fighting. We hypothesized that these dynamics may encode continuous variation in the intensity of an internal aggressive state. Here, we report that these neurons also show line attractor dynamics in head-fixed mice observing aggression. We exploit this finding to identify and perturb line attractor-contributing neurons using 2-photon calcium imaging and holographic optogenetic perturbations. On-manifold perturbations demonstrate that integration and persistent activity are intrinsic properties of these neurons which drive the system along the line attractor, while transient off-manifold perturbations reveal rapid relaxation back into the attractor. Furthermore, stimulation and imaging reveal selective functional connectivity among attractor-contributing neurons. Intriguingly, individual differences among mice in line attractor stability were correlated with the degree of functional connectivity among contributing neurons. Mechanistic modelling indicates that dense subnetwork connectivity and slow neurotransmission are required to explain our empirical findings. Our work bridges circuit and manifold paradigms, shedding light on the intrinsic and operational dynamics of a behaviorally relevant mammalian line attractor.

Distinct lateral hypothalamic CaMKIIα neuronal populations regulate wakefulness and locomotor activity

For nearly a century, evidence has accumulated indicating that the lateral hypothalamus (LH) contains neurons essential to sustain wakefulness. While lesion or inactivation of LH neurons produces a profound increase in sleep, stimulation of inhibitory LH neurons promotes wakefulness. To date, the primary wake-promoting cells that have been identified in the LH are the hypocretin/orexin (Hcrt) neurons, yet these neurons have little impact on total sleep or wake duration across the 24-h period. Recently, we and others have identified other LH populations that increase wakefulness. In the present study, we conducted microendoscopic calcium imaging in the LH concomitant with EEG and locomotor activity (LMA) recordings and found that a subset of LH neurons that express Ca2+/calmodulin-dependent protein kinase IIα (CaMKIIα) are preferentially active during wakefulness. Chemogenetic activation of these neurons induced sustained wakefulness and greatly increased LMA even in the absence of Hcrt signaling. Few LH CaMKIIα-expressing neurons are hypocretinergic or histaminergic while a small but significant proportion are GABAergic. Ablation of LH inhibitory neurons followed by activation of the remaining LH CaMKIIα neurons induced similar levels of wakefulness but blunted the LMA increase. Ablated animals showed no significant changes in sleep architecture but both spontaneous LMA and high theta (8 to 10 Hz) power during wakefulness were reduced. Together, these findings indicate the existence of two subpopulations of LH CaMKIIα neurons: an inhibitory population that promotes locomotion without affecting sleep architecture and an excitatory population that promotes prolonged wakefulness even in the absence of Hcrt signaling.

Identifying behavioral links to neural dynamics of multifiber photometry recordings in a mouse social behavior network

Distributed hypothalamic-midbrain neural circuits orchestrate complex behavioral responses during social interactions. How population-averaged neural activity measured by multi-fiber photometry (MFP) for calcium fluorescence signals correlates with social behaviors is a fundamental question. We propose a state-space analysis framework to characterize mouse MFP data based on dynamic latent variable models, which include continuous-state linear dynamical system (LDS) and discrete-state hidden semi-Markov model (HSMM). We validate these models on extensive MFP recordings during aggressive and mating behaviors in male-male and male-female interactions, respectively. Our results show that these models are capable of capturing both temporal behavioral structure and associated neural states. Overall, these analysis approaches provide an unbiased strategy to examine neural dynamics underlying social behaviors and reveals mechanistic insights into the relevant networks.

Anatomically distributed neural representations of instincts in the hypothalamus

Artificial activation of anatomically localized, genetically defined hypothalamic neuron populations is known to trigger distinct innate behaviors, suggesting a hypothalamic nucleus-centered organization of behavior control. To assess whether the encoding of behavior is similarly anatomically confined, we performed simultaneous neuron recordings across twenty hypothalamic regions in freely moving animals. Here we show that distinct but anatomically distributed neuron ensembles encode the social and fear behavior classes, primarily through mixed selectivity. While behavior class-encoding ensembles were spatially distributed, individual ensembles exhibited strong localization bias. Encoding models identified that behavior actions, but not motion-related variables, explained a large fraction of hypothalamic neuron activity variance. These results identify unexpected complexity in the hypothalamic encoding of instincts and provide a foundation for understanding the role of distributed neural representations in the expression of behaviors driven by hardwired circuits.