A Hypothalamic Midbrain Pathway Essential for Driving Maternal Behaviors

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.

The Hypothalamic Medial Preoptic Area-Paraventricular Nucleus Circuit Modulates Depressive-Like Behaviors in a Mouse Model of Postpartum Depression

Estrogen fluctuations have been implicated in various mood disorders, including perimenopausal and postpartum depression (PPD), likely through complex neural networks. γ-aminobutyric acid-ergic (GABAergic) neurons in the medial preoptic area (MPOA) that express estrogen receptor 1 (ESR1) are essential for the development and expression of depressive-like behaviors in ovarian hormone withdrawal (HW) mice. However, the precise circuit mechanisms through which MPOA GABAergic neurons influence behavior remain incompletely understood. Here, we identified robust projections from MPOA GABAergic neurons to the paraventricular nucleus of the hypothalamus (PVN). In HW mice, chemogenetic activation of MPOA GABAergic neurons targeting PVN attenuated depressive-like behaviors. Conversely, in nonhormone withdrawal (NHW) control mice (which received continuous estrogen), suppression of MPOA GABAergic projections to PVN exacerbated depressive-like behaviors. Further analyses using quantitative polymerase chain reaction and immunostaining identified arginine vasopressin (AVP) as a key neuropeptide in this pathway in the HW mouse model. Chemogenetic inhibition of PVNAVP neurons significantly alleviated depressive-like behaviors in HW mice, while their activation in NHW mice worsened depressive-like behaviors. These behaviors were dependent on AVP expression in PVNAVP neurons. Moreover, in HW mice, chemogenetic inhibition of PVNAVP neurons receiving MPOA input mitigated depressive-like behaviors. Conversely, in NHW mice, activation of these neurons exacerbated depressive-like behaviors. Electrophysiological recordings demonstrated that MPOA GABAergic neurons directly inhibit PVNAVP neurons. Thus, our findings suggest that PVNAVP neurons serve as downstream effectors of MPOA GABAergic neurons via monosynaptic inhibitory signaling to regulate depressive-like behaviors. Targeting this circuit may offer a novel therapeutic strategy for PPD.

Sex-specific hypothalamic neural projection activity drives caregiving in mice

Infant care is critical for survival and healthy development. In laboratory mice, unmated males and females display infant-directed behavior ranging from neglect and aggression to alloparental care. Previous research suggests that excitatory neurons in the perifornical area of the hypothalamus (PeFA) mediate pup-directed aggression. Because medial preoptic area galanin-expressing (MPOAGal) neurons are indispensable for caregiving, we hypothesized that inhibitory MPOAGal projections to PeFA prevent pup-directed aggression. We found that MPOAGal→PeFA projection activity increased during pup approach in both sexes, and alloparental females showed increased projection activity during pup grooming compared to males. Anatomical differences did not explain this disparity in activity between sexes. Optogenetic inhibition of MPOAGal→PeFA projections reduced pup grooming in alloparental females but did not affect male caregiving, while projection stimulation reduced infant-directed aggression in males. Altogether, we show that this projection holds greater significance for female caregiving due to its heightened activity during natural behavior toward pups.

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.

Maternal behavior promotes resilience to adolescent stress in mice through a microglia-neuron axis

Early life experience modulates resilience to stress in later life. Previous research implicated maternal care as a key mediator of behavioral responses to the adversity in adolescence, but details of molecular mechanisms remain elusive. Here, we show social stress activates transcription factor C/EBPβ in mPFC neurons of adolescent mice, which transcriptionally upregulates Dnm1l and promotes mitochondrial dysfunction, thereby conferring stress susceptibility in adolescent mice. Moreover, different maternal separation differentially regulates adolescent stress susceptibility. Mechanistically, this differential effect depends on maternal behavior-stimulated IGF-1, which inhibits neuronal C/EBPβ through mTORC1-induced C/EBPβ-LIP translation. Furthermore, we identify maternal behavior-stimulated IGF-1 is mainly released from mPFC microglia. Notably, increased maternal care under an environmental enrichment condition or maternal behavior impairment induced by repeated MPOAEsr1+ cells inhibition in dams prevents or promotes stress susceptibility via microglial-to-neuronal IGF-1-C/EBPβ-DRP1 signaling. In this work, these findings have unveiled molecular mechanisms by which maternal behavior promotes stress resilience in adolescents.

Post-ejaculatory inhibition of female sexual drive via heterogeneous neuronal ensembles in the medial preoptic area

Male ejaculation acutely suppresses sexual motivation in male mice. In contrast, relatively little is known about how male ejaculation affects sexual motivation and sexual behavior in female mice. How the brain responds to the completion of mating is also unclear. Here, by using a self-paced mating assay, we first demonstrate that female mice show decreased sexual motivation acutely after experiencing male ejaculation. By using brain-wide analysis of activity-dependent labeling, we next pin-pointed the medial preoptic area as a brain region strongly activated during the post-ejaculatory period. Furthermore, using freely moving in vivo calcium imaging to compare the neural activity of inhibitory and excitatory neurons in the medial preoptic area, we revealed that a subset of the neurons in this region responds significantly and specifically to male ejaculation but not to female-to-male sniffing or to male mounting. While there were excitatory and inhibitory neurons that showed increased response to male ejaculation, the response magnitude as well as the proportion of neurons responding to the event was significantly larger in the inhibitory neuron population. Next, by unbiased classification of their responses, we also found a subpopulation of neurons that increase their activity late after the onset of male ejaculation. These neurons were all inhibitory indicating that male ejaculation induces a prolonged inhibitory activity in the medial preoptic area. Lastly, we found that chemogenetic activation of medial preoptic area neurons that were active during the post-ejaculatory period, but not during appetitive or consummatory periods, were sufficient to suppress female sexual motivation. Together, our data illuminate the importance of the medial preoptic area as a brain node which encodes a negative signal that sustains a low sexual motivation state after the female mice experience ejaculation.

Experience-dependent dopamine modulation of male aggression

Numerous studies support the role of dopamine in modulating aggression1,2, but the exact neural mechanisms remain elusive. Here we show that dopaminergic cells in the ventral tegmental area (VTA) can bidirectionally modulate aggression in male mice in an experience-dependent manner. Although VTA dopaminergic cells strongly influence aggression in novice aggressors, they become ineffective in expert aggressors. Furthermore, eliminating dopamine synthesis in the VTA prevents the emergence of aggression in naive mice but leaves aggression intact in expert aggressors. VTA dopamine modulates aggression through the dorsal lateral septum (dLS), a region known for aggression control. Dopamine enables the flow of information from the hippocampus to the dLS by weakening local inhibition in novice aggressors. In expert aggressors, dLS local inhibition naturally weakens, and the ability of dopamine to modulate dLS cells diminishes. Overall, these results reveal a sophisticated role of dopamine in the rise of aggression in adult male mice.

Esr1-Dependent Signaling and Transcriptional Maturation in the Medial Preoptic Area of the Hypothalamus Shapes the Development of Mating Behavior during Adolescence

Mating and other behaviors emerge during adolescence through the coordinated actions of steroid hormone signaling throughout the nervous system and periphery. In this study, we investigated the transcriptional dynamics of the medial preoptic area (MPOA), a critical region for reproductive behavior, using single-cell RNA sequencing (scRNAseq) and in situ hybridization techniques in male and female mice throughout adolescence development. Our findings reveal that estrogen receptor 1 (Esr1) plays a pivotal role in the transcriptional maturation of GABAergic neurons within the MPOA during adolescence. Deletion of the estrogen receptor gene, Esr1, in GABAergic neurons (Vgat+) disrupted the developmental progression of mating behaviors in both sexes, while its deletion in glutamatergic neurons (Vglut2+) had no observable effect. In males and females, these neurons displayed distinct transcriptional trajectories, with hormone-dependent gene expression patterns emerging throughout adolescence and regulated by Esr1. Esr1 deletion in MPOA GABAergic neurons, prior to adolescence, arrested adolescent transcriptional progression of these cells and uncovered sex-specific gene-regulatory networks associated with Esr1 signaling. Our results underscore the critical role of Esr1 in orchestrating sex-specific transcriptional dynamics during adolescence, revealing gene regulatory networks implicated in the development of hypothalamic controlled reproductive behaviors.

Interactions of sex and stress in modulation of ventral tegmental area dopaminergic activity

Dopaminergic (DA) neurons of the ventral tegmental area (VTA) have long been studied for their role in reward prediction and goal-directed behaviors. However, appreciation is growing for a complementary role of VTA DA neurons in responding to aversive stimuli and as critical substrates for behavioral sequelae of stressful experiences. As is the case across neuroscience, the majority of our knowledge about VTA DA neurons comes from studies in male subjects. Recent years have seen an increase in inclusion of female subjects and exploration of sex differences. There is now an emerging body of literature showing that although there are minimal basal structural and functional sex differences in VTA DA neurons, experience-dependent changes in these neurons can differ significantly between males and females. Here, we discuss potential implications of sex differences in VTA function and review recent data on sex differences and similarities of DA neurons at baseline and following stress.

Neuronal Properties in the Lateral Habenula and Adult-Newborn Interactions in Virgin Female and Male Mice

The behavioral interactions between adults and newborns are decisive for the fitness and the survival of offspring across the animal kingdom. In laboratory mice, while virgin females display caregiving behaviors, virgin males are rather neglectful or aggressive toward pups. Despite the importance of these behavioral variations, the underlying neural mechanisms remain poorly understood. Brain regions encoding these behaviors may exhibit sex-dependent functional differences at the baseline. Additionally, these structures might undergo sex-specific plasticity after adults interact with the offspring. Emerging evidence suggests sex-based differences in input connectivity, genetics, and receptor expression of the epithalamic lateral habenula (LHb). Moreover, LHb neuronal activity is instrumental for adult-newborn interactions. However, whether LHb neuronal function varies between sexes and/or undergoes adaptations following interactions with pups has not been fully investigated. In this study, we used in vivo and ex vivo single-cell electrophysiology to examine the basal LHb neuronal activity of virgin female and male mice. In a second set of experiments, we exposed mice to pups and recapitulated sex-based divergent behaviors. Recordings in acute slices showed no alterations in LHb firing properties, regardless of sex or pup exposure. These findings suggest that, although the LHb participates in adult behaviors toward pups, this is not mediated by sex-dependent functional differences or adaptations in the neuronal firing properties. Thus, this study provides new insights into the neural basis of sex-specific adult-newborn behaviors and the role of the LHb in these processes.

In vivo recording from calcitonin receptor-expressing neurons in the medial preoptic area during affiliative social behaviors

Social animals, including mice, are motivated to seek social contact and avoid being alone due to the benefit of the group living in survival and reproductive values. We have previously reported that pup exposure and co-housing with adult female mice can induce the expression of c-Fos in calcitonin receptor (Calcr) neurons located in the medial preoptic area (MPOA) of female mice. These neurons mediate maternal and social contact behaviors among adult virgin females. However, the correlation of the activity of MPOACalcr+ neurons with specific social behaviors remains unclear. In this study, we used in vivo fiber photometry to study MPOACalcr+ neuron activity during affiliative social behaviors. We found that MPOACalcr+ neurons are activated during proactive contact with adult female mice but not during passive contact, suggesting that motivation to seek social contacts is associated with the activation of these neurons. MPOACalcr+ neurons are not activated during contact with non-social objects, such as novel foods and nesting materials, supporting their specific involvement in social behavior. Furthermore, these neurons are more robustly activated during alloparental behaviors such as pup retrieval. Overall, this study demonstrates the involvement of MPOACalcr+ neurons in motivated social interactions with pups and peer females.

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.

Stress drives a switch in sex preference

Distinct brain circuits control sex preferences in mice.

A time for sex: circadian regulation of mammalian sexual and reproductive function

The circadian clock regulates physiological and biochemical processes in nearly every species. Sexual and reproductive behaviors are two processes controlled by the circadian timing system. Evidence supporting the importance of proper clock function on fertility comes from several lines of work demonstrating that misalignment of biological rhythms or disrupted function of the body's master clock, such as occurs from repeated shift work or chronic jet lag, negatively impacts reproduction by interfering with both male and female fertility. Along these lines, dysregulation of clock genes leads to impairments in fertility within mammals, and disruption of circadian clock timing negatively impacts sex hormone levels and semen quality in males, and it leads to ovulatory deficiencies in females. Here, we review the current understanding of the circadian modulation of both male and female reproductive hormones-from animal models to humans. Further, we discuss neural circuits within the hypothalamus that may regulate circadian changes in mammalian sexual behavior and reproduction, and we explore how knowledge of such circuits in animal models may help to improve human sexual function, fertility, and reproduction.

The neurobiology of parenting and infant-evoked aggression

Parenting behavior comprises a variety of adult-infant and adult-adult interactions across multiple timescales. The state transition from nonparent to parent requires an extensive reorganization of individual priorities and physiology and is facilitated by combinatorial hormone action on specific cell types that are integrated throughout interconnected and brainwide neuronal circuits. In this review, we take a comprehensive approach to integrate historical and current literature on each of these topics across multiple species, with a focus on rodents. New and emerging molecular, circuit-based, and computational technologies have recently been used to address outstanding gaps in our current framework of knowledge on infant-directed behavior. This work is raising fundamental questions about the interplay between instinctive and learned components of parenting and the mutual regulation of affiliative versus agonistic infant-directed behaviors in health and disease. Whenever possible, we point to how these technologies have helped gain novel insights and opened new avenues of research into the neurobiology of parenting. We hope this review will serve as an introduction for those new to the field, a comprehensive resource for those already studying parenting, and a guidepost for designing future studies.

Aggression experience and observation promote shared behavioral and neural changes

The ability to observe the social behavior of others and use observed information to bias future action is a fundamental building block of social cognition1,2. A foundational question is whether social observation and experience engage common circuit mechanisms that enable behavioral change. While classic studies on social learning have shown that aggressive behaviors can be learned through observation3, it remains unclear whether aggression observation promotes persistent neural changes that generalize to new contexts. Here, to directly compare the effects of aggression experience and observation at brain-wide scale, we develop a strategy to perform large-scale cell-type specific recordings across subcortical networks for social behavior control and learning. We record longitudinally while animals "train" through direct experience or observation, then probe shared differences in behavior and neural activity in a novel "hard" aggression context. Using supervised and unsupervised methods for behavioral quantification, we detect unique signatures of a shared behavioral strategy not present in animals with no training. During observation, we find widespread activation that mimics experience in networks for behavior generation, with critical differences in signals associated with reward and threat learning. After observation, we observe that changes persist into the novel aggression context, with increased similarity in the neural dynamics between experience and observation groups. Network-level modeling reveals persistent shared changes to a core aggression network, with widespread decoupling of inhibition from a key hypothalamic output region. This demonstrates that "experience-like" activity during observation can recruit a shared plasticity mechanism that biases behavior toward adaptive defensive strategies in new contexts.

Flexible adjustment of oxytocin neuron activity in mouse dams revealed by microendoscopy

Oxytocin (OT) neurons in the hypothalamic paraventricular nucleus (PVH) play an important role in various physiological and behavioral processes, including the initiation of milk ejection and the regulation of maternal behaviors. However, their activity patterns at the single-cell level remain poorly understood. Using microendoscopic Ca2+ imaging in freely moving mouse dams, we demonstrate highly correlated pulsatile activity among individual OT neurons during lactation. The number of OT neurons engaged in the pulsatile activity significantly increased, along with a broadening of individual waveforms in the mid-lactation stage. Notably, only ~10% of the imaged OT neurons exhibited a significantly elevated response during pup retrieval, a hallmark of maternal behaviors, with a magnitude smaller than that observed during lactation. Collectively, these findings demonstrate the utility of microendoscopic imaging for PVH OT neurons and highlight the flexible adjustments of their individual activity patterns in freely behaving mouse dams.

Stress and parental behaviors

In nearly all mammalian species, newborn pups are weak and vulnerable, relying heavily on care and protection from parents for survival. Thus, developmentally hardwired neural circuits are in place to ensure the timely expression of parental behaviors. Furthermore, several neurochemical systems, including estrogen, oxytocin, and dopamine, facilitate the emergence and expression of parental behaviors. However, stress can adversely affect these systems, impairing parental behaviors. In this review, we will summarize our current knowledge regarding the impact of stress on pup-directed behavior circuits that lead to infant neglect, abuse, and, in extreme cases, killing. We will discuss various stressors that influence parental behaviors at different life stages and how stress induces changes in the neurochemical systems that support parental care, ultimately leading to its poor performance.

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.

GABAergic Retinal Ganglion Cells Projecting to the Superior Colliculus Mediate the Looming-Evoked Flight Response

The looming stimulus-evoked flight response to approaching predators is a defensive behavior in most animals. However, how looming stimuli are detected in the retina and transmitted to the brain remains unclear. Here, we report that a group of GABAergic retinal ganglion cells (RGCs) projecting to the superior colliculus (SC) transmit looming signals from the retina to the brain, mediating the looming-evoked flight behavior by releasing GABA. GAD2-Cre and vGAT-Cre transgenic mice were used in combination with Cre-activated anterograde or retrograde tracer viruses to map the inputs to specific GABAergic RGC circuits. Optogenetic technology was used to assess the function of SC-projecting GABAergic RGCs (scpgRGCs) in the SC. FDIO-DTA (Flp-dependent Double-Floxed Inverted Open reading frame-Diphtheria toxin) combined with the FLP (Florfenicol, Lincomycin & Prednisolone) approach was used to ablate or silence scpgRGCs. In the mouse retina, GABAergic RGCs project to different brain areas, including the SC. ScpgRGCs are monosynaptically connected to parvalbumin-positive SC neurons known to be required for the looming-evoked flight response. Optogenetic activation of scpgRGCs triggers GABA-mediated inhibition in SC neurons. Ablation or silencing of scpgRGCs compromises looming-evoked flight responses without affecting image-forming functions. Our study reveals that scpgRGCs control the looming-evoked flight response by regulating SC neurons via GABA, providing novel insight into the regulation of innate defensive behaviors.

Hormonal Actions in the Medial Preoptic Area Governing Parental Behavior: Novel Insights From New Tools

The importance of hormones in mediating a behavioral transition in mammals from a virgin or nonparenting state to parental state was established around 50 years ago. Extensive research has since revealed a highly conserved neural circuit that underlies parental behavior both between sexes and between mammalian species. Within this circuit, hormonal action in the medial preoptic area of the hypothalamus (MPOA) has been shown to be key in timing the onset of parental behavior with the birth of offspring. However, the mechanism underlying how hormones act in the MPOA to facilitate this change in behavior has been unclear. Technical advances in neuroscience, including single cell sequencing, novel transgenic approaches, calcium imaging, and optogenetics, have recently been harnessed to reveal new insights into maternal behavior. This review aims to highlight how the use of these tools has shaped our understanding about which aspects of maternal behavior are regulated by specific hormone activity within the MPOA, how hormone-sensitive MPOA neurons integrate within the wider neural circuit that governs maternal behavior, and how maternal hormones drive changes in MPOA neuronal function during different reproductive states. Finally, we review our current understanding of hormonal modulation of MPOA-mediated paternal behavior in males.

Hormone Regulation of Corticotropin-Releasing Factor Receptor 1 in the Female Mouse Brain

INTRODUCTION

Corticotropin-releasing factor receptor 1 (CRFR1) is a key regulator of neuroendocrine and behavioral stress responses. Previous studies have demonstrated that CRFR1 in certain hypothalamic and preoptic brain areas is modified by chronic stress and during the postpartum period in female mice, although the potential hormonal contributors to these changes are unknown.

METHODS

This study focused on determining the contributions of hormones associated with stress and the maternal period (glucocorticoids, prolactin, estradiol/progesterone) on CRFR1 levels using a CRFR1-GFP reporter mouse line and immunohistochemistry.

RESULTS

Administration of dexamethasone, an agonist of the glucocorticoid receptor, elevated CRFR1 in the anteroventral periventricular nucleus (AVPV/PeN) and paraventricular hypothalamus (PVN) with no changes found in the medial preoptic area (MPOA) or arcuate nucleus. Treatment with prolactin for 5 days elevated CRFR1 levels in the MPOA with no changes in other regions. Finally, we utilized the hormone-simulated pseudopregnancy (HSP) paradigm to mimic changes in estradiol and progesterone across pregnancy and the early postpartum period. Female mice receiving HSP treatment, as well as mice receiving HSP treatment that then underwent 5 days of estrogen withdrawal (EW), showed alterations in CRFR1 relative to control groups that mirrored changes previously reported in postpartum mice. Specifically, CRFR1 levels increased in the AVPV/PeN and decreased in the MPOA and PVN, with no changes found in the arcuate nucleus. HSP- and EW-treated mice also showed decreases in tyrosine hydroxylase-expressing neurons in the AVPV/PeN.

DISCUSSION/CONCLUSION

Overall, these hormone-induced changes in stress-regulating CRFR1 neurons may impact behavioral and neuroendocrine stress responses.

Excitation-inhibition imbalance in medial preoptic area circuits underlies chronic stress-induced depression-like states

Dysregulation of brain homeostasis is associated with neuropsychiatric conditions such as major depressive disorder. However, underlying neural-circuit mechanisms remain not well-understood. We show in mice that chronic restraint stress (CRS) and social defeat stress (SDS) are both associated with disruption of excitation (E)-inhibition (I) balance, with increased E/I ratios, in medial preoptic area (MPOA) circuits, but through affecting different neuronal types. CRS results in elevated activity in glutamatergic neurons, and their suppression mitigates CRS-induced depressive-like behaviors. Paraventricular hypothalamic input to these neurons contributes to induction but not expression of depressive-like behaviors. Their projections to ventral tegmental area and periaqueductal gray/dorsal raphe suppress midbrain dopaminergic and serotonergic activity, respectively, and mediate expression of divergent depressive-like symptoms. By contrast, SDS results in reduced activity of GABAergic neurons, and their activation alleviates SDS-induced depressive-like behaviors. Thus, E/I imbalance with relatively increased excitation in MPOA circuits may be a general mechanism underlying depression caused by different etiological factors.

Is melanin-concentrating hormone in the medial preoptic area a signal for the decline of maternal care in late postpartum?

This manuscript proposes that melanin-concentrating hormone (MCH) in the medial preoptic area (MPOA) is an neurochemical signal evolved to trigger the declining process of maternal care. MCH in the MPOA appears only after parturition and is progressively increased with the progression of lactation, while maternal behavior declines progressively. Intra-MPOA injection of MCH decreases active maternal responses. MCH is also highly responsive to infant characteristics and maternal condition. Behavioral changes induced by MCH in late postpartum period are conducive to the decline of infant-directed maternal behavior. The MPOA MCH system may mediate the maternal behavior decline by suppressing the maternal approach motivation and/or increasing maternal withdrawal via its inhibitory action onto the mesolimbic dopamine D1/D2 receptors and its stimulating action on serotonin 5-HT2C receptors in the ventral tegmental area. Research into the MCH maternal effects will enhance our understanding of the neurochemical mechanisms underlying the maternal behavior decline.

In vivo magnetogenetics for cell-type-specific targeting and modulation of brain circuits

Neuromodulation technologies are crucial for investigating neuronal connectivity and brain function. Magnetic neuromodulation offers wireless and remote deep brain stimulations that are lacking in optogenetic- and wired-electrode-based tools. However, due to the limited understanding of working principles and poorly designed magnetic operating systems, earlier magnetic approaches have yet to be utilized. Furthermore, despite its importance in neuroscience research, cell-type-specific magnetic neuromodulation has remained elusive. Here we present a nanomaterials-based magnetogenetic toolbox, in conjunction with Cre-loxP technology, to selectively activate genetically encoded Piezo1 ion channels in targeted neuronal populations via torque generated by the nanomagnetic actuators in vitro and in vivo. We demonstrate this cell-type-targeting magnetic approach for remote and spatiotemporal precise control of deep brain neural activity in multiple behavioural models, such as bidirectional feeding control, long-term neuromodulation for weight control in obese mice and wireless modulation of social behaviours in multiple mice in the same physical space. Our study demonstrates the potential of cell-type-specific magnetogenetics as an effective and reliable research tool for life sciences, especially in wireless, long-term and freely behaving animals.

Distinct populations of lateral preoptic nucleus neurons jointly contribute to depressive-like behaviors through divergent projections in male mice

The lateral preoptic area (LPO) is a component of the hypothalamus involved in various physiological functions including sleep-wakefulness transition, thermoregulation, and water-salt balance. In this study, we discovered that distinct LPO excitatory neurons project separately to the aversive processing center lateral habenula (LHb) and the reward processing hub ventral tegmental area (VTA). Following chronic restraint stress (CRS), the LHb-projecting and VTA-projecting LPO neurons exhibited increased and decreased neuronal activities, respectively. Optogenetic activation of LHb-projecting LPO excitatory neurons and LPO excitatory neuronal terminals within LHb evoked aversion and avoidance behaviors, while activation of VTA-projecting LPO excitatory neurons and LPO excitatory neuronal terminals within VTA produced preference and exploratory behaviors in mice. Furthermore, either optogenetic inhibition of LHb-projecting LPO excitatory neurons or activation of VTA-projecting LPO excitatory neurons during CRS effectively prevented the development of depressive-like behaviors. Our study unveils, for the first-time, divergent pathways originating from LPO that regulate opposite affective states in mice and implicates that an imbalance of their activities could lead to depressive-like behaviors. These circuitries represent promising therapeutic targets to relieve emotional dysfunctions in neuropsychiatric disorders.

A Hypothalamic Circuit that Modulates Feeding and Parenting Behaviors

Across mammalian species, new mothers undergo considerable behavioral changes to nurture their offspring and meet the caloric demands of milk production1-5. While many neural circuits underlying feeding and parenting behaviors are well characterized6-9, it is unclear how these different circuits interact and adapt during lactation. Here, we characterized the transcriptomic changes in the arcuate nucleus (ARC) and the medial preoptic area (MPOA) of the mouse hypothalamus in response to lactation and hunger. Furthermore, we showed that heightened appetite in lactating mice was accompanied by increased activity of hunger-promoting agouti-related peptide (AgRP) neurons in the ARC. To assess the strength of hunger versus maternal drives, we designed a conflict assay where female mice chose between a food source or a chamber containing pups and nesting material. Although food-deprived lactating mothers prioritized parenting over feeding, hunger reduced the duration and disrupted the sequences of parenting behaviors in both lactating and virgin females. We discovered that ARCAgRP neurons directly inhibit bombesin receptor subtype-3 (BRS3) neurons in the MPOA, a population that governs both parenting and satiety. Selective activation of this ARCAgRP to MPOABRS3 circuit shifted behaviors from parenting to food-seeking. Thus, hypothalamic networks are modulated by physiological states and work antagonistically during the prioritization of competing motivated behaviors.

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.

Computer vision analysis of mother-infant interaction identified efficient pup retrieval in V1b receptor knockout mice

Close contact between lactating rodent mothers and their infants is essential for effective nursing. Whether the mother's effort to retrieve the infants to their nest requires the vasopressin-signaling via V1b receptor has not been fully defined. To address this question, V1b receptor knockout (V1bKO) and control mice were analyzed in pup retrieval test. Because an exploring mother in a new test cage randomly accessed to multiple infants in changing backgrounds over time, a computer vision-based deep learning analysis was applied to continuously calculate the distances between the mother and the infants as a parameter of their relationship. In an open-field, a virgin female V1bKO mice entered fewer times into the center area and moved shorter distances than wild-type (WT). While this behavioral pattern persisted in V1bKO mother, the pup retrieval test demonstrated that total distances between a V1bKO mother and infants came closer in a shorter time than with a WT mother. Moreover, in the medial preoptic area, parts of the V1b receptor transcripts were detected in galanin- and c-fos-positive neurons following maternal stimulation by infants. This research highlights the effectiveness of deep learning analysis in evaluating the mother-infant relationship and the critical role of V1b receptor in pup retrieval during the early lactation phase.

Roadmap for maternal behavior research in domestic dogs: lessons from decades of laboratory rodent work

Maternal behavior research in laboratory rats has revealed important behavioral and neurobiological mechanisms governing the onset, maintenance and decline of maternal behavior. However, the extent to which these mechanisms are evolutionarily conserved across species is less clear. This manuscript proposes that examining these mechanisms in dogs may be a viable approach to test their generality and help bridge the gap between rodent and human research, as domestic dogs show greater individual differences and exhibit more human-like maternal characteristics than rodents. These aspects represent advantages over rodent models, which in turn allow systems biological approaches not available in rodents. Additionally, domestic dogs share similar social environments with humans, suffer from the same mental disorders as humans, and can be treated with the same medications. This paper begins with a summary of key findings and theoretical developments from decades of rat maternal behavior research, followed by a literature review of the extant maternal behavior research on dogs and related methodology, highlighting the unique behavioral characteristics of dog maternal behavior and similarities and differences from rat maternal behavior. Finally, several knowledge gaps in dog maternal behavior research, as well as the future research in this area is discussed. It concludes that research on dog maternal behavior will not only advance our understanding of the universality of the neurobiological and behavioral mechanisms in maternal behavior, but also improve our understanding of risk factors associated with postpartum mental disorders.

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.

Activation of lateral preoptic neurons is associated with nest-building in male mice

Nest-building behavior is a widely observed innate behavior. A nest provides animals with a secure environment for parenting, sleep, feeding, reproduction, and temperature maintenance. Since animal infants spend their time in a nest, nest-building behavior has been generally studied as parental behaviors, and the medial preoptic area (MPOA) neurons are known to be involved in parental nest-building. However, nest-building of singly housed male mice has been less examined. Here we show that male mice spent longer time in nest-building at the early to middle dark phase and at the end of the dark phase. These two periods are followed by sleep-rich periods. When a nest was removed and fresh nest material was introduced, both male and female mice built nests at Zeitgeber time (ZT) 6, but not at ZT12. Using Fos-immunostaining combined with double in situ hybridization of Vgat and Vglut2, we found that Vgat- and Vglut2-positive cells of the lateral preoptic area (LPOA) were the only hypothalamic neuron population that exhibited a greater number of activated cells in response to fresh nest material at ZT6, compared to being naturally awake at ZT12. Fos-positive LPOA neurons were negative for estrogen receptor 1 (Esr1). Both Vgat-positive and Vglut2-positive neurons in both the LPOA and MPOA were activated at pup retrieval by male mice. Our findings suggest the possibility that GABAergic and glutamatergic neurons in the LPOA are associated with nest-building behavior in male mice.

Gestational immune activation disrupts hypothalamic neurocircuits of maternal care behavior

Immune activation is one of the most common complications during pregnancy, predominantly evoked by viral infections. Nevertheless, how immune activation affects mother-offspring relationships postpartum remains unknown. Here, by using the polyinosinic-polycytidylic acid (Poly I:C) model of gestational infection we show that viral-like immune activation at mid-gestation persistently changes hypothalamic neurocircuit parameters in mouse dams and, consequently, is adverse to parenting behavior. Poly I:C-exposed dams favor non-pup-directed exploratory behavior at the expense of pup retrieval. These behavioral deficits are underlain by dendrite pruning and lesser immediate early gene activation in Galanin (Gal)+ neurons with dam-specific transcriptional signatures that reside in the medial preoptic area (mPOA). Reduced activation of an exclusively inhibitory contingent of these distal-projecting Gal+ neurons allows for increased feed-forward inhibition onto putative dopaminergic neurons in the ventral tegmental area (VTA) in Poly I:C-exposed dams. Notably, destabilized VTA output specifically accompanies post-pup retrieval epochs. We suggest that gestational immunogenic insults bias both threat processing and reward perception, manifesting as disfavored infant caregiving.

Independent inhibitory control mechanisms for aggressive motivation and action

Social behaviors often consist of a motivational phase followed by action. Here we show that neurons in the ventromedial hypothalamus ventrolateral area (VMHvl) of mice encode the temporal sequence of aggressive motivation to action. The VMHvl receives local inhibitory input (VMHvl shell) and long-range input from the medial preoptic area (MPO) with functional coupling to neurons with specific temporal profiles. Encoding models reveal that during aggression, VMHvl shellvgat+ activity peaks at the start of an attack, whereas activity from the MPO-VMHvlvgat+ input peaks at specific interaction endpoints. Activation of the MPO-VMHvlvgat+ input promotes and prolongs a low motivation state, whereas activation of VMHvl shellvgat+ results in action-related deficits, acutely terminating attack. Moreover, stimulation of MPO-VMHvlvgat+ input is positively valenced and anxiolytic. Together, these data demonstrate how distinct inhibitory inputs to the hypothalamus can independently gate the motivational and action phases of aggression through a single locus of control.

Lights, fiber, action! A primer on in vivo fiber photometry

Fiber photometry is a key technique for characterizing brain-behavior relationships in vivo. Initially, it was primarily used to report calcium dynamics as a proxy for neural activity via genetically encoded indicators. This generated new insights into brain functions including movement, memory, and motivation at the level of defined circuits and cell types. Recently, the opportunity for discovery with fiber photometry has exploded with the development of an extensive range of fluorescent sensors for biomolecules including neuromodulators and peptides that were previously inaccessible in vivo. This critical advance, combined with the new availability of affordable "plug-and-play" recording systems, has made monitoring molecules with high spatiotemporal precision during behavior highly accessible. However, while opening exciting new avenues for research, the rapid expansion in fiber photometry applications has occurred without coordination or consensus on best practices. Here, we provide a comprehensive guide to help end-users execute, analyze, and suitably interpret fiber photometry studies.

A dedicated hypothalamic oxytocin circuit controls aversive social learning

To survive in a complex social group, one needs to know who to approach and, more importantly, who to avoid. In mice, a single defeat causes the losing mouse to stay away from the winner for weeks1. Here through a series of functional manipulation and recording experiments, we identify oxytocin neurons in the retrochiasmatic supraoptic nucleus (SOROXT) and oxytocin-receptor-expressing cells in the anterior subdivision of the ventromedial hypothalamus, ventrolateral part (aVMHvlOXTR) as a key circuit motif for defeat-induced social avoidance. Before defeat, aVMHvlOXTR cells minimally respond to aggressor cues. During defeat, aVMHvlOXTR cells are highly activated and, with the help of an exclusive oxytocin supply from the SOR, potentiate their responses to aggressor cues. After defeat, strong aggressor-induced aVMHvlOXTR cell activation drives the animal to avoid the aggressor and minimizes future defeat. Our study uncovers a neural process that supports rapid social learning caused by defeat and highlights the importance of the brain oxytocin system in social plasticity.

Neural basis for behavioral plasticity during the parental life-stage transition in mice

Parental care plays a crucial role in the physical and mental well-being of mammalian offspring. Although sexually naïve male mice, as well as certain strains of female mice, display aggression toward pups, they exhibit heightened parental caregiving behaviors as they approach the time of anticipating their offspring. In this Mini Review, I provide a concise overview of the current understanding of distinct limbic neural types and their circuits governing both aggressive and caregiving behaviors toward infant mice. Subsequently, I delve into recent advancements in the understanding of the molecular, cellular, and neural circuit mechanisms that regulate behavioral plasticity during the transition to parenthood, with a specific focus on the sex steroid hormone estrogen and neural hormone oxytocin. Additionally, I explore potential sex-related differences and highlight some critical unanswered questions that warrant further investigation.

Distinct roles of amylin and oxytocin signaling in intrafamilial social behaviors at the medial preoptic area of common marmosets

Calcitonin receptor (Calcr) and its brain ligand amylin in the medial preoptic area (MPOA) are found to be critically involved in infant care and social contact behaviors in mice. In primates, however, the evidence is limited to an excitotoxic lesion study of the Calcr-expressing MPOA subregion (cMPOA) in a family-living primate species, the common marmoset. The present study utilized pharmacological manipulations of the cMPOA and shows that reversible inactivation of the cMPOA abolishes infant-care behaviors in sibling marmosets without affecting other social or non-social behaviors. Amylin-expressing neurons in the marmoset MPOA are distributed in the vicinity of oxytocin neurons in the anterior paraventricular nucleus of the hypothalamus. While amylin infusion facilitates infant carrying selectively, an oxytocin's inverse agonist, atosiban, reduces physical contact with non-infant family members without grossly affecting infant care. These data suggest that the amylin and oxytocin signaling mediate intrafamilial social interactions in a complementary manner in marmosets.

Transcriptionally defined amygdala subpopulations play distinct roles in innate social behaviors

Social behaviors are innate and supported by dedicated neural circuits, but the molecular identities of these circuits and how they are established developmentally and shaped by experience remain unclear. Here we show that medial amygdala (MeA) cells originating from two embryonically parcellated developmental lineages have distinct response patterns and functions in social behavior in male mice. MeA cells expressing the transcription factor Foxp2 (MeAFoxp2) are specialized for processing male conspecific cues and are essential for adult inter-male aggression. By contrast, MeA cells derived from the Dbx1 lineage (MeADbx1) respond broadly to social cues, respond strongly during ejaculation and are not essential for male aggression. Furthermore, MeAFoxp2 and MeADbx1 cells show differential anatomical and functional connectivity. Altogether, our results suggest a developmentally hardwired aggression circuit at the MeA level and a lineage-based circuit organization by which a cell's embryonic transcription factor profile determines its social information representation and behavioral relevance during adulthood.

Neural Circuit Transitions Supporting Developmentally Specific Social Behavior

Environmentally appropriate social behavior is critical for survival across the lifespan. To support this flexible behavior, the brain must rapidly perform numerous computations taking into account sensation, memory, motor-control, and many other systems. Further complicating this process, individuals must perform distinct social behaviors adapted to the unique demands of each developmental stage; indeed, the social behaviors of the newborn would not be appropriate in adulthood and vice versa. However, our understanding of the neural circuit transitions supporting these behavioral transitions has been limited. Recent advances in neural circuit dissection tools, as well as adaptation of these tools for use at early time points, has helped uncover several novel mechanisms supporting developmentally appropriate social behavior. This review, and associated Minisymposium, bring together social neuroscience research across numerous model organisms and ages. Together, this work highlights developmentally regulated neural mechanisms and functional transitions in the roles of the sensory cortex, prefrontal cortex, amygdala, habenula, and the thalamus to support social interaction from infancy to adulthood. These studies underscore the need for synthesis across varied model organisms and across ages to advance our understanding of flexible social behavior.

Neurocircuits for motivation

The nervous system coordinates various motivated behaviors such as feeding, drinking, and escape to promote survival and evolutionary fitness. Although the precise behavioral repertoires required for distinct motivated behaviors are diverse, common features such as approach or avoidance suggest that common brain substrates are required for a wide range of motivated behaviors. In this Review, I describe a framework by which neural circuits specified for some innate drives regulate the activity of ventral tegmental area (VTA) dopamine neurons to reinforce ongoing or planned actions to fulfill motivational demands. This framework may explain why signaling from VTA dopamine neurons is ubiquitously involved in many types of diverse volitional motivated actions, as well as how sensory and interoceptive cues can initiate specific goal-directed actions.

Hypothalamic control of innate social behaviors

Sexual, parental, and aggressive behaviors are central to the reproductive success of individuals and species survival and thus are supported by hardwired neural circuits. The reproductive behavior control column (RBCC), which comprises the medial preoptic nucleus (MPN), the ventrolateral part of the ventromedial hypothalamus (VMHvl), and the ventral premammillary nucleus (PMv), is essential for all social behaviors. The RBCC integrates diverse hormonal and metabolic cues and adjusts an animal's physical activity, hence the chance of social encounters. The RBCC further engages the mesolimbic dopamine system to maintain social interest and reinforces cues and actions that are time-locked with social behaviors. We propose that the RBCC and brainstem form a dual-control system for generating moment-to-moment social actions. This Review summarizes recent progress regarding the identities of RBCC cells and their pathways that drive different aspects of social behaviors.

Neural dynamics in the limbic system during male social behaviors

Sexual and aggressive behaviors are vital for species survival and individual reproductive success. Although many limbic regions have been found relevant to these behaviors, how social cues are represented across regions and how the network activity generates each behavior remains elusive. To answer these questions, we utilize multi-fiber photometry (MFP) to simultaneously record Ca2+ signals of estrogen receptor alpha (Esr1)-expressing cells from 13 limbic regions in male mice during mating and fighting. We find that conspecific sensory information and social action signals are widely distributed in the limbic system and can be decoded from the network activity. Cross-region correlation analysis reveals striking increases in the network functional connectivity during the social action initiation phase, whereas late copulation is accompanied by a "dissociated" network state. Based on the response patterns, we propose a mating-biased network (MBN) and an aggression-biased network (ABN) for mediating male sexual and aggressive behaviors, respectively.

Hormone-mediated neural remodeling orchestrates parenting onset during pregnancy

During pregnancy, physiological adaptations prepare the female body for the challenges of motherhood. Becoming a parent also requires behavioral adaptations. Such adaptations can occur as early as during pregnancy, but how pregnancy hormones remodel parenting circuits to instruct preparatory behavioral changes remains unknown. We found that action of estradiol and progesterone on galanin (Gal)-expressing neurons in the mouse medial preoptic area (MPOA) is critical for pregnancy-induced parental behavior. Whereas estradiol silences MPOAGal neurons and paradoxically increases their excitability, progesterone permanently rewires this circuit node by promoting dendritic spine formation and recruitment of excitatory synaptic inputs. This MPOAGal-specific neural remodeling sparsens population activity in vivo and results in persistently stronger, more selective responses to pup stimuli. Pregnancy hormones thus remodel parenting circuits in anticipation of future behavioral need.

Sexually dimorphic oxytocin receptor-expressing (OXTR) neurons in the anteroventral periventricular nucleus (AVPV) in the postpartum female mouse are involved in maternal behavior

Maternal care is crucial for the survival and development of offspring. Oxytocin modulates maternal behavior by binding to oxytocin receptors (OXTRs) in various parts of the brain. Previously, we showed that OXTRs are expressed in the anteroventral periventricular nucleus (AVPV) of female, but not male mice. Because the AVPV is involved in the regulation of maternal behavior and oxytocin enhances its induction, this finding leads to the hypothesis that the female specific population of OXTR neurons in the AVPV regulates maternal behavior. To address this hypothesis, OXTR-Venus reporter mice were used to assess if expression levels of OXTR in the AVPV are changed during the postpartum period. The total number of OXTR-Venus neurons was significantly greater in postpartum dams compared to virgin females. To assess efferent projections of the AVPV-OXTR neurons, a Cre-dependent fluorescent protein (tdTomato) expressing a viral vector was injected into one side of the AVPV of female OXTR-Cre mice. Fibers expressing tdTomato were found in hypothalamic areas containing oxytocin neurons (the supraoptic and paraventricular nuclei) and the midbrain areas (the ventral tegmental area and periaqueductal gray) that are involved in the regulation of maternal motivation. To assess if activity of the AVPV-OXTR neurons is involved in the regulation of maternal behaviors, a chemogenetic approach was employed. Specific inhibition of activity of AVPV-OXTR neurons completely abolished pup retrieval and nest building behaviors. Collectively, these findings demonstrate that AVPV-OXTR neurons in postpartum female mice constitute an important node in the neural circuitry that regulates maternal behavior.

Instinct to insight: Neural correlates of ethological strategy learning

In ethological behaviors like parenting, animals innately follow stereotyped patterns of choices to decide between uncertain outcomes but can learn to modify their strategies to incorporate new information. For example, female mice in a T-maze instinctively use spatial-memory to search for pups where they last found them but can learn more efficient strategies employing pup-associated acoustic cues. We uncovered neural correlates for transitioning between these innate and learned strategies. Auditory cortex (ACx) was required during learning. ACx firing at the nest increased with learning and correlated with subsequent search speed but not outcome. Surprisingly, ACx suppression rather than facilitation during search was more prognostic of correct sound-cued outcomes - even before adopting a sound-cued strategy. Meanwhile medial prefrontal cortex encoded the last pup location, but this decayed as the spatial-memory strategy declined. Our results suggest a neural competition between a weakening spatial-memory and strengthening sound-cued neural representation to mediate strategy switches.

The medial preoptic area mediates depressive-like behaviors induced by ovarian hormone withdrawal through distinct GABAergic projections

Fluctuations in reproductive hormone levels are associated with mood disruptions in women, such as in postpartum and perimenopausal depression. However, the neural circuit mechanisms remain unclear. Here we report that medial preoptic area (MPOA) GABAergic neurons mediate multifaceted depressive-like behaviors in female mice after ovarian hormone withdrawal (HW), which can be attributed to downregulation of activity in Esr1 (estrogen receptor-1)-expressing GABAergic neurons. Enhancing activity of these neurons ameliorates depressive-like behaviors in HW-treated mice, whereas reducing their activity results in expression of these behaviors. Two separate subpopulations mediate different symptoms: a subpopulation projecting to the ventral tegmental area (VTA) mediates anhedonia and another projecting to the periaqueductal gray mediates immobility. These projections enhance activity of dopaminergic neurons in the VTA and serotonergic neurons in the dorsal raphe, respectively, with increased release of dopamine and serotonin, possibly through disinhibition mechanisms. Thus, the MPOA is a hub that mediates depressive-like behaviors resulting from transitions in reproductive hormone levels.

Neural circuitry for maternal oxytocin release induced by infant cries

Oxytocin is a neuropeptide that is important for maternal physiology and childcare, including parturition and milk ejection during nursing1-6. Suckling triggers the release of oxytocin, but other sensory cues-specifically, infant cries-can increase the levels of oxytocin in new human mothers7, which indicates that cries can activate hypothalamic oxytocin neurons. Here we describe a neural circuit that routes auditory information about infant vocalizations to mouse oxytocin neurons. We performed in vivo electrophysiological recordings and photometry from identified oxytocin neurons in awake maternal mice that were presented with pup calls. We found that oxytocin neurons responded to pup vocalizations, but not to pure tones, through input from the posterior intralaminar thalamus, and that repetitive thalamic stimulation induced lasting disinhibition of oxytocin neurons. This circuit gates central oxytocin release and maternal behaviour in response to calls, providing a mechanism for the integration of sensory cues from the offspring in maternal endocrine networks to ensure modulation of brain state for efficient parenting.