Modulation of social behavior by distinct vasopressin sources

Sex-dependent effects of ethanol withdrawal from a single- and repeated binge episode exposures on social anxiety-like behavior and neuropeptide gene expression in adolescent rats

Ethanol withdrawal sensitivity is a risk factor for the development of alcohol use disorder. Heavy episodic drinking during adolescence often encompasses repeated periods of withdrawal. Adolescent intermittent ethanol exposure of laboratory rodents produces several neurobiological deficits that differ between sexes, but the sensitivity to withdrawal as a contributor to the observed sex differences is not clear. The current study assessed the impact of acute withdrawal from a single- and repeated binge ethanol episodes during adolescence as well as protracted abstinence from repeated binge episodes on social anxiety-like behavior (indexed via significant decreases of social investigation) as well as oxytocin (OXT) and vasopressin (AVP) system gene expression in the hypothalamus (HYP) and central amygdala (CeA) in male and female Sprague Dawley rats. Females displayed social anxiety-like behavior during withdrawal from a single binge episode, whereas both sexes showed social anxiety-like changes following acute withdrawal from repeated binge episodes. After a period of protracted abstinence, only males still displayed ethanol-associated social alterations. Analysis of gene expression in separate, non-socially tested subjects revealed that withdrawal from repeated binge episodes during adolescence increased AVP gene expression in the HYP of males and decreased it in females. Males also displayed increased AVP and OXTR gene expression during acute withdrawal from repeated binge episodes in the CeA, with these changes persisting into adulthood. Together, these findings suggest that adolescent females are sensitive to withdrawal from both acute and repeated ethanol exposures, whereas males are sensitive to withdrawal from repeated ethanol exposures, with affective and transcriptional changes persisting into adulthood.

Exploring neuronal markers and early social environment influence in divergent quail lines selected for social motivation

Many species, including humans exhibit a wide range of social behaviors that are crucial for the adaptation and survival of most species. Brain organization and function are shaped by genetic and environmental factors, although their precise contributions have been relatively understudied in the context of artificial selection. We used divergent lines of quail selected on their high versus low level of motivation to approach a group of conspecifics (S + and S-, respectively) to investigate the influence of genetic selection and early social environment on sociability. We observed distinct sex- and brain-region-specific expression patterns of three neuronal markers: mesotocin, and vasotocin, the avian homologues of mammalian oxytocin and vasopressin, as well as aromatase, the enzyme that converts androgens into estrogens. These markers displayed pronounced and neuroanatomically specific differences between S + and S- quail. Additionally, in a second experiment, we assessed the influence of early social environment on social skills in juvenile birds. Mixing S + and S- resulted in more S- males approaching the group without affecting the sociability of S + or other behaviors, suggesting that the early social environment may influence the results of genetic selection. In conclusion, the divergent quail lines offer a valuable model for unraveling the neuronal and behavioral mechanisms underlying social behaviors.

Hypothalamic vasopressin neural densities are higher in male Mongolian gerbils after separation from a pair bond partner and may facilitate behavior to form a new bond

Although pair bonding has been studied for several decades, only somewhat recently have researchers began studying the neural consequences of separation from a pair bond partner. Here we examined the impact of partner separation on the socially monogamous Mongolian gerbil. Using a within-subjects design, we assessed nonsocial, nonreproductive, and reproductive behavior in male gerbils pre- and post- either 4 weeks of cohabitation with or separation from a pair bond partner. We then conducted an immediate early gene study to examine the influence of partner separation on hypothalamic oxytocin and vasopressin neural responses to interactions with a novel, opposite-sex conspecific.

Severe PTSD is marked by reduced oxytocin and elevated vasopressin

Neuroendocrine analyses of posttraumatic stress disorder (PTSD) have generally focused on hypothalamic-pituitary-adrenal (HPA) axis alterations. In the present analyses, we examine two additional neuroendocrine factors that have been previously implicated in biological stress responses: oxytocin (OT) and arginine vasopressin (AVP). Here we examined basal neuropeptide status in military veterans clinically diagnosed with PTSD (n = 29) and in two non-traumatized comparison groups with previous stress exposure (n = 11 SWAT trainees and n = 21 ultramarathon runners). PTSD patients showed low levels of plasma OT and high levels of AVP. The ratio of AVP/OT robustly related to PTSD status, and emerged as a statistically plausible mediator of relationships between the number of personal traumatic experiences and subsequent PTSD symptom burden. Over the course of behavioral therapy for PTSD, measures of OT showed a significant but modest normalization. Plasma cortisol levels were not statistically different among the three groups. This study suggests that AVP/OT ratios may represent a neuroendocrine predictor of severe PTSD, as well as a potential treatment response biomarker.

Changes in peripheral oxytocin and vasopressin during a silent month-long Insight meditation retreat

Background

Given its putative roles in mediating prosocial behavior, attachment bonds, and stress physiology, oxytocin modulation has been hypothesized to be a biological correlate of the salubrious effects of meditation practice. Here we investigated the effects of a month-long silent meditation retreat on changes in oxytocin, and the related hormone and vasopressin, in relation to psychosocial changes in attachment style, anxiety, personality measures, and feelings of social connectedness with fellow meditators.

Methods

Plasma oxytocin and vasopressin and self-report questionnaires were measured in retreat participants (n = 28) at the beginning of, and 3 weeks into, a residential meditation retreat. Control participants (n = 34), who were similar in age, gender, and meditation experience, were also assessed across a 3-week interval. Linear mixed effects models were used to assess outcomes.

Results

The retreat group showed a small but significant decrease in oxytocin compared to controls who showed no change. In the retreat group, higher openness to experience at Time 1 predicted greater reductions in oxytocin during the retreat, and lower oxytocin at Time 2 was related to stronger feelings of personal connection with fellow meditators. The changes in oxytocin were not related to attachment style or anxiety. Vasopressin decreased over time across both groups, suggesting no specific effect of retreat.

Conclusion

These preliminary findings suggest that meditation training in the context of a silent residential retreat may reduce circulating levels of oxytocin. We interpret this finding from multiple theoretical perspectives, discussing key measurement limitations and proposing future study designs that may help to differentiate the effects of different meditation practices and contexts on oxytocin signaling.

A vasopressin circuit that modulates mouse social investigation and anxiety-like behavior in a sex-specific manner

One of the largest sex differences in brain neurochemistry is the expression of the neuropeptide arginine vasopressin (AVP) within the vertebrate brain, with males having more AVP cells in the bed nucleus of the stria terminalis (BNST) than females. Despite the long-standing implication of AVP in social and anxiety-like behaviors, the circuitry underlying AVP's control of these behaviors is still not well defined. Using optogenetic approaches, we show that inhibiting AVP BNST cells reduces social investigation in males, but not in females, whereas stimulating these cells increases social investigation in both sexes, but more so in males. These cells may facilitate male social investigation through their projections to the lateral septum (LS), an area with the highest density of sexually differentiated AVP innervation in the brain, as optogenetic stimulation of BNST AVP → LS increased social investigation and anxiety-like behavior in males but not in females; the same stimulation also caused a biphasic response of LS cells ex vivo. Blocking the vasopressin 1a receptor (V1aR) in the LS eliminated all these responses. Together, these findings establish a sexually differentiated role for BNST AVP cells in the control of social investigation and anxiety-like behavior, likely mediated by their projections to the LS.

Adolescent social isolation disrupts developmental tuning of neuropeptide circuits in the hypothalamus to amygdala regulating social and defensive behavior

Engaging in positive social (i.e., prosocial) interactions during adolescence acts to modulate neural circuits that determine adult adaptive behavior. While accumulating evidence indicates that a strong craving for prosocial behavior contributes to sustaining neural development, the consequences of social deprivation during adolescence on social neural circuits, including those involving oxytocin (OXT) and vasopressin (AVP), are poorly characterized. We evaluated adaptive behaviors in socially isolated mice, including anxiety-like, social, and defensive behaviors, along with OXT and AVP neural profiles in relevant brain regions. Social isolation from postnatal day (P-)22 to P-48 induced enhanced defensive and exploratory behaviors, in nonsocial and social contexts. Unlike OXT neurons, AVP+ cell density in the paraventricular nucleus of the hypothalamus increases with age in males. Social isolation also modulated gene expression in the medial amygdala (MeA), including the upregulation of OXT receptors in males and the downregulation of AVP1a receptors in both sexes. Socially isolated mice showed an enhanced defensive, anogenital approach toward a novel adult female during direct social interactions. Subsequent c-Fos mapping revealed diminished neural activity in restricted brain areas, including the MeA, lateral septum, and posterior intralaminar nucleus of the thalamus, in socially isolated mice. These data indicate that neural signals arising from daily social interactions invoke region-specific modification of neuropeptide expression that coordinates with altered defensiveness and neural responsivities, including OXT- and AVP-projecting regions. The present findings indicate an involvement of OXT and AVP circuits in adolescent neural and behavioral plasticity that is tuned by daily social interaction.

Exploring the influence of stress on aggressive behavior and sexual function: Role of neuromodulator pathways and epigenetics

Stress is a complex and multifaceted phenomenon that can significantly influence both aggressive behavior and sexual function. This review explores the intricate relationship between stress, neuromodulator pathways, and epigenetics, shedding light on the various mechanisms that underlie these connections. While the role of stress in both aggression and sexual behavior is well-documented, the mechanisms through which it exerts its effects are multifarious and not yet fully understood. The review begins by delving into the potential influence of stress on the Hypothalamic-Pituitary-Adrenal (HPA) axis, glucocorticoids, and the neuromodulators involved in the stress response. The intricate interplay between these systems, which encompasses the regulation of stress hormones, is central to understanding how stress may contribute to aggressive behavior and sexual function. Several neuromodulator pathways are implicated in both stress and behavior regulation. We explore the roles of norepinephrine, serotonin, oxytocin, and androgens in mediating the effects of stress on aggression and sexual function. It is important to distinguish between general sexual behavior, sexual motivation, and the distinct category of "sexual aggression" as separate constructs, each necessitating specific examination. Additionally, epigenetic mechanisms emerge as crucial factors that link stress to changes in gene expression patterns and, subsequently, to behavior. We then discuss how epigenetic modifications can occur in response to stress exposure, altering the regulation of genes associated with stress, aggression, and sexual function. While numerous studies support the association between epigenetic changes and stress-induced behavior, more research is necessary to establish definitive links. Throughout this exploration, it becomes increasingly clear that the relationship between stress, neuromodulator pathways, and epigenetics is intricate and multifaceted. The review emphasizes the need for further research, particularly in the context of human studies, to provide clinical significance and to validate the existing findings from animal models. By better understanding how stress influences aggressive behavior and sexual function through neuromodulator pathways and epigenetic modifications, this research aims to contribute to the development of innovative protocols of precision medicine and more effective strategies for managing the consequences of stress on human behavior. This may also pave way for further research into risk factors and underlying mechanisms that may associate stress with sexual aggression which finds application not only in neuroscience, but also law, ethics, and the humanities in general.

An integrated single-cell RNA-seq atlas of the mouse hypothalamic paraventricular nucleus links transcriptomic and functional types

The hypothalamic paraventricular nucleus (PVN) is a highly complex brain region that is crucial for homeostatic regulation through neuroendocrine signaling, outflow of the autonomic nervous system, and projections to other brain areas. In the past years, single-cell datasets of the hypothalamus have contributed immensely to the current understanding of the diverse hypothalamic cellular composition. While the PVN has been adequately classified functionally, its molecular classification is currently still insufficient. To address this, we created a detailed atlas of PVN transcriptomic cell types by integrating various PVN single-cell datasets into a recently published hypothalamus single-cell transcriptome atlas. Furthermore, we functionally profiled transcriptomic cell types, based on relevant literature, existing retrograde tracing data, and existing single-cell data of a PVN-projection target region. Finally, we validated our findings with immunofluorescent stainings. In our PVN atlas dataset, we identify the well-known different neuropeptide types, each composed of multiple novel subtypes. We identify Avp-Tac1, Avp-Th, Oxt-Foxp1, Crh-Nr3c1, and Trh-Nfib as the most important neuroendocrine subtypes based on markers described in literature. To characterize the preautonomic functional population, we integrated a single-cell retrograde tracing study of spinally projecting preautonomic neurons into our PVN atlas. We identify these (presympathetic) neurons to cocluster with the Adarb2+ clusters in our dataset. Further, we identify the expression of receptors for Crh, Oxt, Penk, Sst, and Trh in the dorsal motor nucleus of the vagus, a key region that the pre-parasympathetic PVN neurons project to. Finally, we identify Trh-Ucn3 and Brs3-Adarb2 as some centrally projecting populations. In conclusion, our study presents a detailed overview of the transcriptomic cell types of the murine PVN and provides a first attempt to resolve functionality for the identified populations.

Male-specific vasotocin expression in the medaka tuberal hypothalamus: Androgen dependence and probable role in aggression

Terrestrial vertebrates have a population of androgen-dependent vasotocin (VT)-expressing neurons in the extended amygdala that are more abundant in males and mediate male-typical social behaviors, including aggression. Teleosts lack these neurons but instead have novel male-specific VT-expressing neurons in the tuberal hypothalamus. Here we found in medaka that vt expression in these neurons is dependent on post-pubertal gonadal androgens and that androgens can act on these neurons to directly stimulate vt transcription via the androgen receptor subtype Ara. Furthermore, administration of exogenous VT induced aggression in females and alterations in the androgen milieu led to correlated changes in the levels of tuberal hypothalamic vt expression and aggression in both sexes. However, genetic ablation of vt failed to prevent androgen-induced aggression in females. Collectively, our results demonstrate a marked androgen dependence of male-specific vt expression in the teleost tuberal hypothalamus, although its relevance to male-typical aggression needs to be further validated.

A vasopressin circuit that modulates sex-specific social interest and anxiety-like behavior in mice

One of the largest sex differences in brain neurochemistry is the male-biased expression of the neuropeptide arginine vasopressin (AVP) within the vertebrate social brain. Despite the long-standing implication of AVP in social and anxiety-like behavior, the precise circuitry and anatomical substrate underlying its control are still poorly understood. By employing optogenetic manipulation of AVP cells within the bed nucleus of the stria terminalis (BNST), we have unveiled a central role for these cells in promoting social investigation, with a more pronounced role in males relative to females. These cells facilitate male social investigation and anxiety-like behavior through their projections to the lateral septum (LS), an area with the highest density of sexually-dimorphic AVP fibers. Blocking the vasopressin 1a receptor (V1aR) in the LS eliminated stimulation-mediated increases in these behaviors. Together, these findings establish a distinct BNST AVP → LS V1aR circuit that modulates sex-specific social interest and anxiety-like behavior.