Hormones and Behavior

Disruptions to maternal behaviors that emerge during the peripartum period have been shown to have lasting physiological and behavioral consequences for offspring. In addition to effects on offspring, disrupted maternal behaviors have been associated with peripartum mood and anxiety disorders. Therefore, it is critical for the wellbeing of both mother and offspring to identify upstream risk factors for the disruption of maternal behavior. We have previously found that pubertal stress leads to a blunted hypothalamic-pituitary-adrenal (HPA) axis response in peripartum humans and mice. Given that dysfunction of the HPA axis is associated with both PMADs and disrupted maternal behavior, we examined how pubertal stress influenced maternal behavior throughout peripartum in mice using a pup retrieval test. We found that pubertal stress led to faster pup retrieval, but a less predictable pattern of maternal behavior, as well as a blunted HPA axis response during pregnancy. We also examined whether maternal pubertal stress influenced offspring behavior in adolescence and adulthood. We found sex-specific differences in risk-taking behavior during adolescence that are no longer present in adulthood. Finally, we used in situ hybridization to examine gene expression during pregnancy in the medial preoptic area of the hypothalamus, a region implicated in maternal behavior. Following pubertal stress, we found cell-type specific changes in the expression of genes necessary for the expression of maternal behavior. Collectively, these findings contribute to our understanding of upstream risk factors for peripartum disruptions to maternal behavior and the lasting effects of pubertal stress on both mother and offspring.

Courtship is an essential component of reproductive success for many species and many courtship behaviors, such as vocalization, are energetically demanding. In order to successfully balance investment in courtship with feeding and foraging, individuals must be aware of their current energy balance, and hormonal signals of energetic state have been found to influence social signal effort across a variety of species. Ghrelin is one hormone that plays an important role in regulating energy balance by signaling hunger and promoting feeding. Previous studies have investigated the role of ghrelin in courtship, aggression, and mating behavior. In this study, we build on prior work by investigating the effects of ghrelin on ultrasonic vocalizations (USV) and other courtship behaviors of male mice. We expand on previous research by observing ghrelin's effects over longer interactions, allowing us to understand how ghrelin impacts the dynamics of USV production over time. Our results show that while males initially vocally court females at a high rate regardless of treatment, ghrelin reduces overall USV production by increasing the rate of decline of vocalization. Surprisingly, despite its effects on vocal courtship, we found no significant differences in the production or timing of other, non-vocal, courtship behaviors. This study deepens our understanding of the role of hormones traditionally associated with controlling hunger and feeding in regulating social behaviors.

Oxytocin (OT) and vasopressin (AVP) are neuropeptide hormones involved in regulating animal social behavior and a broad spectrum of physiological processes. Although their distributions are well documented in neuroendocrine regions of the forebrain and midbrain, their expression in the hindbrain remains poorly understood. Here, we used immunohistochemistry to quantify OT and AVP immunoreactive puncta within three auditory brainstem nuclei, the lateral superior olive (LSO), the medial superior olive (MSO), and the medial nucleus of the trapezoid body (MNTB) in six wild-caught rodent species differing in sociality. We also quantified the volume of these nuclei and examined variation in total brain volume across species and sociality. OT and AVP puncta count differed among species and social groups. Group-living species exhibited higher OT and AVP puncta counts than monogamous and solitary species in the LSO and MNTB. In the MSO, OT puncta counts did not differ among social groups, whereas AVP puncta counts were higher in group-living than in monogamous and solitary species. Total brain volume and the volumes of the MNTB and MSO differed among species, but not across social groups, whereas LSO volume did not differ among species or sociality. These findings revealed sociality-related variation in OT and AVP immunoreactive puncta within auditory brainstem circuits and suggest that neuropeptide signaling within early auditory brainstem pathways may contribute to the neural integration of social and auditory information.

Social bonds are fundamental to health and well-being, and their disruption through partner separation is associated with significant physiological and psychological consequences. The kappa opioid receptor (KOR) system has been proposed as a key modulator of oxytocin (OT) release during partner separation, with prolonged separation hypothesized to trigger KOR downregulation in the paraventricular nucleus of the hypothalamus that disinhibits OT release over time (Bales & Rogers, 2022). However, this model has been difficult to assess non-invasively in primates. The present study used positron emission tomography (PET) with the KOR-selective radiotracer [11C]GR103545 to examine KOR availability in vivo across brain regions implicated in social bonding and separation distress in 16 pair-bonded titi monkeys using a within-subject two-week separation paradigm. Plasma OT, cerebrospinal fluid OT, and plasma cortisol were collected at each scan as complementary indices of peripheral and central OT signaling and physiological stress. We hypothesized that long-term separation would downregulate KORs in the hypothalamus and pituitary, indexed by reduced non-displaceable binding potential (BPND), consistent with the Bales and Rogers model, and increase plasma OT consistent with KOR downregulation disinhibiting OT release. Partner separation significantly elevated plasma cortisol in both sexes, confirming the physiological stress of the manipulation. A significant Condition x Sex interaction was observed for plasma OT, reflecting a crossover pattern in which males, who had significantly higher plasma OT than females at baseline, showed a significant decrease during separation while females showed a non-significant increase, though the sex difference during separation did not reach significance. KOR availability was significantly reduced in the nucleus accumbens during separation, with a non-significant trend toward reduction in the anterior cingulate cortex, while no significant condition effects were observed in the remaining a priori chosen regions. No significant sex effects or Condition x Sex interactions were observed in any a priori chosen PET region. Together, these findings provide the first in vivo neuroimaging evidence of KOR system engagement during partner separation in a pair-bonded primate species, and reveal a sex-dependent OT response to separation that extends and adds nuance to the Bales and Rogers (2022) framework.

RationaleThe -opioid receptor (MOR) is widely expressed across tissues and plays crucial roles in pain and stress responses, social behaviour, and immune regulation. Recent evidence indicates seasonal variation in in vivo MOR signalling; for example, short photoperiods are associated with reduced central MOR availability, increased MOR expression in brown adipose tissue (BAT), and strengthened brain-BAT interactions. However, despite this coupling with photoperiod, it remains unclear whether static daylength and dynamically changing photoperiods exert distinct effects, as adaptation to photoperiod transitions may itself induce stress-related modulation of the MOR system. Elucidating how seasonal, stress-related adaptations influence MOR signalling is essential for advancing our understanding of seasonal fluctuations in mood and stress regulation. MethodsWe compared rats housed under seasonal photoperiod cycling with those maintained under constant photoperiod conditions, using ex vivo radioligand binding to directly assess MOR density in central and peripheral tissues. ResultsRats exposed to seasonal photoperiod cycling showed markedly reduced inter-individual variability in MOR density in both the brain (including the cerebellum and striatum) and peripheral tissues (adrenal glands), whereas no tissues exhibited substantially increased variability. ConclusionsThese findings demonstrate that seasonal photoperiod cycling stabilizes MOR dynamics at the population level, suggesting stress-related synchronization of MOR signalling. The findings deepen our understanding of seasonal effects on endogenous MOR signalling, and further underscore the role of seasonal light variation in modulating mood-related processes.

In mammals, sex differences in the brain arise from genetic and hormonal factors, including organizational effects of perinatal testosterone. Epigenetic mechanisms including DNA methylation and demethylation have emerged as critical mediators of brain masculinization; specifically, their regulatory enzymes are upregulated in neonatal mice during the critical period of sexual differentiation, with their inhibition abolishing sex-specific cellular phenotypes. Here, we assessed sex differences in gene expression of the DNA demethylation machinery (Tet1, Tet2, Tet3, Gadd45a, Gadd45b and Tdg) during and after the critical period, and examined how these differences relate to the oxytocinergic system. mRNA expression was measured in the prefrontal cortex (PFC), preoptic area (POA) and paraventricular nucleus of the hypothalamus (PVN) at postnatal day (P) 7 and P18. At P7, males showed higher expression of all six genes than females in PFC, with no differences in POA or PVN; by P18, no regional differences remained. Oxytocin (OXT) immunoreactivity was surveyed across periventricular nucleus (Pe), anteroventral periventricular nucleus (AVPe), POA, PVN and supraoptic nucleus (SON). OXT was undetectable in the POA, AVPe and Pe at P7, and no sex differences were found in PVN or SON at either age, or in AVPe at P18. At P18, females showed higher OXT-immunoreactivity in the Pe and POA, than males. For Oxtr, qPCR revealed higher mRNA expression in the PFC of males at P7, with no other regional differences and none remaining at P18. Together, these findings suggest that sex differences in oxytocinergic regions arise from sex-specific epigenetic regulation during the critical period, and that perinatal testosterone may program DNA methylation dynamics underlying sex-specific gene expression in the developing brain. Our results support a model in which testosterone-dependent epigenetic mechanisms contribute to the sexual differentiation of neuroendocrine circuits, linking hormonal signals to long-term brain organization.

Prenatal stress influences brain development; however, its long-term, region-specific effects on brain aging in males and females remain insufficiently characterized. This study examined the impact of unpredictable mild prenatal stress on behavior, cognition, and maternal care in C57BL/6J mice at middle (12 months) and old (18 months) ages. Stressed dams showed fragmented, unpredictable maternal behaviors, creating a stressful postnatal environment without impairing caregiving capacity. Both male and female offspring were born with lower birth weights and showed rapid postnatal growth, a trajectory associated with central insulin resistance and hippocampal signaling deficits. Sex-specific behavioral differences emerged with age. Middle-aged stressed males exhibited anhedonia, which progressed to hyperactivity, stereotypy, and persistent spatial memory deficits in old age. These outcomes corresponded with accelerated fronto-striatal decline, likely mediated by insulin resistance and increased rigidity of medial prefrontal cortex structures due to diminished local estrogenic activity. In contrast, middle-aged stressed females displayed hypoactivity and reduced anxiety, later developing anhedonia in old age while maintaining hippocampus-dependent memory. In females, this pattern supports a model in which a neuroestrogen - and growth factor-dependent feedback loop transiently preserves hippocampal plasticity but compromises dopaminergic function in reward circuits. This balance may deteriorate with reproductive senescence. Both sexes retained cognitive flexibility, indicating domain-specific rather than global cognitive impairment. These findings demonstrate that excessive prenatal glucocorticoid exposure and unpredictable postnatal care produce a combined hormonal and metabolic insult, resulting in sexually divergent trajectories of brain aging. The results underscore the necessity of incorporating sex as a biological variable in fetal programming research across the lifespan.

Male-biased cooperative behaviours that produce public goods (male services) are widespread in primates. Recent behavioural studies suggest that male services may function beyond paternal investment, either as displays of competitive ability or as honest signals eliciting female choice. Because these hypotheses make contrasting predictions about the physiological state of service providers, endocrine measures offer a complementary approach for distinguishing between them. We investigated whether long-term testosterone and cortisol concentrations, measured from hair samples, were associated with four male services in wild vervet monkeys: alarm calling, participation in between-group conflicts (BGCs), leading river crossings, and sentinelling. Testosterone and cortisol concentrations increased with male competitive status, measured as a combination of dominance rank and recent rank trajectory, particularly during the mating period, establishing the endocrine profile associated with competition. In contrast, most male services showed few relationships with hormone concentrations: participation in BGCs was associated with lower cortisol concentrations and, to a lesser extent, lower testosterone concentrations. Because BGC participation is the strongest predictor of male mating frequency in this population, these findings indicate that males contributing to BGCs present an endocrine profile distinct from that associated with competitive state and instead support the prediction that high-quality males, irrespective of their dominance rank, can perform costly cooperative behaviours while maintaining relatively low physiological costs. More broadly, our results provide physiological support for reputation-based partner choice as a mechanism contributing to the maintenance of male services in primates.

AimThe aim of the present study was to determine whether pharmacological inhibition of aldosterone synthesis during the stress-hyporesponsive period (SHRP) affects behaviour and adrenocortical stress responsiveness later in development and whether these effects differ between males and females. MethodsNewborn Wistar rat pups (males n=40, females n=40) were treated with aldosterone synthase inhibitor FAD286 (30 mg/kg per day, orally) or vehicle from PND3 to PND9. To verify the pharmacodynamic action of FAD286, serum and adrenal glands from 10-day-old pups were analysed. The remaining pups were weaned on PND21 and underwent open-field (PND23), elevated plus-maze (PND29) and salt-preference testing. At PND46, half of each group was exposed to restraint stress for 120 min. ResultsIn 10-day-old pups, treatment with FAD286 resulted in increased gene expression of CYP11B2 (aldosterone synthase) and CYP11B1 (11-beta-hydroxylase) in the adrenal glands, increased serum levels of corticosterone, and decreased concentrations of serum aldosterone. FAD286 did not modify the general locomotor activity assessed in juvenile rats. Inhibition of aldosterone synthase by FAD286 resulted in altered anxiety-like behaviour in a sex-dependent manner. Postnatal FAD286 treatment led to increased anxiety-like behaviour in female, but not male rats. During adolescence, early FAD286 treatment increased overall aldosterone concentrations without altering the aldosterone response to restraint. Basal corticosterone concentrations were unchanged, whereas the response to restraint was enhanced. ConclusionsThe present study demonstrates that transient inhibition of aldosterone synthesis during the SHRP led to alterations in anxiety-related behaviour and adrenocortical regulation later in development, with some behavioural effects being sex-dependent.

Social behaviors are critical for survival and change dramatically over the lifespan. Adolescence is a critical period of development during which social novelty seeking peaks before declining into adulthood. Adolescence is also a time of pronounced neural circuit refinement as excess synapses are eliminated. One critical mechanism supporting this maturation of neural circuits is microglial pruning of synapses through the classical complement signaling cascade. However, it remains unclear how microglial pruning of the neural circuitry supporting social novelty preference shapes the trajectory of this behavior during adolescence. To address this, we blocked microglial complement-dependent pruning during adolescence by injecting neutrophil inhibitory factor (NIF; blocks the adhesion of ligands to CD11b/C3 receptor) in the lateral septum (LS), a key node in the social circuitry supporting social novelty preference, in male mice. We found that NIF administration into the LS during adolescence increased preference for the novel social chamber over the familiar as compared to control PBS administration. LS-NIF treatment had no impact on anxiety-like behavior in the light-dark box test and no effect on sociability. LS-NIF treatment also decreased the expression of immune-related genes in the LS as compared to PBS treatment. These data support the hypothesis that complement-dependent microglial synaptic elimination in the LS is critical for the developmental progression of social novelty preference.

Stressors experienced during the postnatal period may increase vulnerability to mental health disorders, including postpartum depression and anxiety. In rodents, maternal separation (MS) has been shown to alter behaviours in dams, but these observations have been made almost exclusively in rats and thus robust mouse models of postpartum mental health disorders using this stressor remain limited. Here we first examined, in mice, the effects of MS on maternal caregiving and on anxiety- and depressive-like behaviours. As stress-induced inflammatory activation in the gut-brain axis has been associated with behavioural alterations in non-postpartum contexts, changes in pro-inflammatory cytokines and tight junction proteins in the brain and intestinal tract were also examined. Female C57BL/6N mice were assigned to a No Separation (NS) or a MS condition that consisted of 3-hour daily separation sessions from postnatal days (P) 2 to 14. Maternal care behaviours were assessed on P3 and P7, followed by anxiety- and depressive-like behaviours on P22 and P23, and the collection of the medial prefrontal cortex (mPFC) and colon on P24 to determine the expression of selected genes. Caregiving patterns in MS dams fluctuated throughout the early postnatal period. Although behaviours and gene expression outcomes remained unchanged by MS, grooming time in the splash test was correlated with the expression of different genes in the mPFC. These findings suggest that C57BL/6 mouse dams may be less sensitive to the actions of MS on behaviour and on brain and intestinal markers of inflammation and barrier permeability, at least when examined shortly after weaning.

Fear conditioning studies have historically relied on freezing as the primary measure of conditioned fear despite evidence that defensive responding is behaviorally diverse and sexually dimorphic. The endogenous opioid system, particularly mu-opioid receptor (MOR) signaling, is known to regulate fear learning and conditioned analgesia, yet its role in alternative fear-related behaviors and sex differences remains unclear. Here, we investigated the effects of systemic naloxone administration prior to auditory fear conditioning on freezing, darting, shock responsivity, and ultrasonic vocalizations (USVs) in male and female rats. Adult Sprague Dawley rats received naloxone (5 mg/kg, i.p.) or saline prior to conditioning and underwent fear recall testing 24 hours later. Naloxone produced sex- and behavior-specific effects across conditioning and recall. During conditioning, naloxone increased freezing in males during baseline and early tone presentations, while females exhibited reduced shock-response velocity and increased post-shock freezing. Naloxone did not significantly alter darting or USV production during conditioning. During recall, freezing behavior did not differ across groups. Naloxone-treated females, however, exhibited a distinct alarm-calling pattern, with fewer callers overall but increased call output among those that vocalized. These findings suggest that MOR antagonism differentially alters distinct components of fear expression in a sex-dependent manner and support the idea that freezing and alarm calling may reflect separable aspects of fear processing.

Stressful experiences are a major risk factor for the development of neuropsychiatric disorders in vulnerable individuals. Identifying features that can distinguish stress-susceptible from resilient individuals remains a central goal in stress neurobiology. Due to the routine exclusion of female subjects from stress research or the use of male-defined criteria in behavioral characterization of subjects post-stress, female stress responses and vulnerability profiles remain poorly understood. This work aimed to gain a better understanding of sex-specific stress responses to social defeat stress. Here, we used a novel paired male-female social defeat paradigm and tracked subjects longitudinally in a ''two-hit'' design to evaluate responses to both acute social defeat stress (ASDS) and chronic social defeat stress (CSDS), and to determine how prior stress exposure influences subsequent vulnerability. We found that both ASDS and CSDS induces changes in social avoidance/approach behavior in males but not females, as measured by a classic social interaction ratio. Prior ASDS exposure enhanced susceptibility to subsequent CSDS most clearly in males, with females displaying specific changes in corner zone occupancy. Furthermore, we observed divergent anxiety profiles between males and females in a post-stress behavioral battery. Finally, females exhibited specific stress-related locomotor responses following ASDS. Together, these findings suggest that females may adopt distinct behavioral strategies following social defeat stress.

Social animals must identify, evaluate, and appropriately respond to other individuals, often relying on multiple sources of information to guide context-dependent behavior. While individual recognition is thought to be widespread and critical for many social interactions (e.g. territoriality, dominance hierarchies), convincing demonstrations across animals beyond class-level recognition remain rare. Further, the cues animals use to recognize individuals remains poorly understood, especially in natural environments where they are exposed to numerous cues which may require cue integration. Here, we examine how socially dominant males of the African cichlid fish, Astatotilapia burtoni, use individual recognition to modulate aggression and whether this process depends on the spatial context. Using naturalistic experimental setups, we exposed males to familiar and unfamiliar neighbors while systematically manipulating spatial location and presenting a neighbor either singly or simultaneously to simulate competing social cues. Additionally, we measured circulating testosterone to assess endocrine correlates of recognition and aggression. We found that focal males habituated to familiar neighbors only when they remained in a consistent territorial location, demonstrating that spatial context is important for recognition. Further, when familiar and unfamiliar neighbors were presented simultaneously, males preferentially aggressed toward unfamiliar rival and adjust their aggressive response to the perceived threat of their neighbors, indicating that identity-based threat assessment is maintained under competing social demands. Together, our results show that recognition is a flexible, multi-faceted process that depends on the integration of identity and contextual information to guide territorial decision-making under dynamic social conditions.

Early-life stress (ELS) has been associated with increases in obesity and anxiety and affects males and females in different ways. Animal and human studies indicate that ELS has maladaptive effects on brain development due, in part, to disruptions in the expression of genes that include brain-derived neurotrophic factor (BDNF). Our previous studies identified a cis-regulatory element (CRE, BE5.1) within BDNF intron-3 that harbours a SNP associated with obesity and anxiety. We used maternal separation (MS) to examine the role of BE5.1 in controlling resilience to the maladaptive effects of ELS. At 9-11 weeks, BE5.1KO mice experience a delay in weight gain compared to WT mice, a phenotype partly reversed by MS in BE5.1KO females. The effects of either MS or BE5.1KO decreased anxiety-like behaviour in males whereas MS had little effect in females who displayed increased anxiety-like behaviour in animals lacking BE5.1. We also found that social behaviours are influenced by BE5.1 deletion in females but are more influenced by MS in males. Furthermore, deletion of BE5.1 and MS together significantly decreased marble burying behaviour in male mice, an effect negated by diazepam. RNA-seq analyses suggest that, in hypothalamus, BE5.1 is required to stabilize or down-regulate the transcription of 26 key genes, with diverse neuroregulatory roles, in response to MS as these 26 genes are strongly upregulated in the absence of BE5.1. We also provide evidence that three of these genes; Prkcg, Foxg1 and Mef2c, modulate BE5.1 activity in an allele-specific manner. Taken together, these results suggest that the BE5.1CRE acts as a buffer element that protects against the maladaptive effects of MS on gene expression and later life behaviours in a sex-dependent manner.

Objective: Women with premenstrual syndrome (PMS) experience affective lability, irritability, depressed mood, and anxiety during the late luteal phase of the menstrual cycle. Stress reactivity may contribute to the development of these symptoms, yet neural correlates remain unexplored. We examined neural, behavioral and endocrine stress responses across menstrual cycle phases in women with and without PMS. Methods: 26 women with PMS and 24 women without PMS participated in two fMRI sessions, during the mid-follicular (days 5 to 11) and late-luteal phases (days -7 to -1). Participants completed the Montreal Imaging Stress Task (MIST). Subjective stress ratings and salivary cortisol were collected at six time points before and after stress induction. Stress-related brain activation was assessed using whole-brain and region-of-interest analyses. Results: Subjective stress ratings increased as expected from before to after the MIST, with no group or phase differences. Salivary cortisol was significantly higher during the mid-follicular phase, with no group effect or significant pre-post MIST difference. While the stress task elicited activation patterns in stress-related regions, whole-brain analysis revealed no significant effects of group (PMS vs. no PMS) or menstrual cycle phase (follicular vs. luteal) on the neural stress response. Considering premenstrual symptom severity as a predictor revealed significant group-by-symptom severity interactions in the right inferior frontal gyrus and the right superior temporal gyrus. Conclusion: Using a within-subject repeated-measures design, we found neural responses to psychosocial stress to be stable across menstrual cycle phases. Individual differences in symptom severity may nevertheless be associated with differences in stress-related brain activation.

The integration of separate memories sharing overlapping elements allows for inferring relationships between events that have never been experienced together. Recent findings indicate that stress impairs this process of mnemonic inference, which may have important implications for stress-related psychopathologies. However, the mechanisms underlying such impairments remain largely unknown. To elucidate the neuroendocrine mechanisms by which stress affects mnemonic inference, mice were first trained on two sets of auditory visual cue associations. Afterwards, one of the visual cues was paired with reward. Mnemonic inference was probed by examining reward seeking behavior in response to the auditory cues alone. Control mice successfully inferred the auditory cue outcome association, selectively seeking reward in response to the auditory cue associated with the rewarded visual cue. In contrast, systemic administration of the stress hormone corticosterone before testing impaired inference accuracy, leading mice to seek reward to both auditory cues. Corticosterone administration was accompanied by increased noradrenergic activity, and stimulation of noradrenergic signaling with yohimbine similarly disrupted inference accuracy. Conversely, the beta adrenoceptor antagonist propranolol prevented the corticosterone induced impairment, indicating that corticosterone effects depend on concurrent noradrenergic activation. At the neural level, the corticosterone induced mnemonic inference impairment was associated with enhanced GABAergic inhibition of pyramidal neurons in the hippocampal CA3 region. Furthermore, hippocampal administration of the GABAA receptor antagonist bicuculline prevented the corticosterone induced impairment in mnemonic inference. Together, these findings identify a glucocorticoid noradrenergic mechanism that disrupts mnemonic inference through enhanced GABAergic inhibition in hippocampal CA3, providing an account of how stress hormones impair inferential memory.

Early-life psychosocial adversity increases vulnerability to stress-related disorders and may begin as early as prior to conception via maternal stress. Consequently, early-life stress (ELS) in offspring may accumulate across early development. The short-allele variant of the serotonin transporter (SERT) gene has been implicated in depression risk and higher anxiety sensitivity following stress exposure, but for cumulative ELS it is unknown whether behavioral effects depend on the SERT genotype. In this study, we used heterozygous SERT knockout (SERT+/-) rats to model reduced SERT expression similar to human short-allele carriers. To investigate the effects of cumulative ELS on offspring behavioral phenotype, dams were exposed to stress before, during and after pregnancy, combined with offspring postnatal maternal separation. Cognitive, affective, and social behaviors were assessed in wild-type (WT) and SERT+/- (HET) male and female adults. Maternal care and anhedonia-like behaviors in dams were also assessed. Dams exposed to the cumulative stress (STR) displayed increased arched-back licking and grooming compared to controls (CTR). In the offspring, HET rats showed increased social investigation and tended to display hyperactivity compared to WT. Anxiety-like behavior was higher in HET females compared to WT females, with no genotype differences in males. Independent of genotype, STR rats consumed less sucrose and showed impaired object recognition compared to CTR; however, HET-STR rats performed better in the object recognition than WT-STR rats. A significant SERT genotype x cumulative ELS x sex interaction revealed opposing, sex-dependent effects on anxiety-like behavior. HET-STR females showed more anxiety-like responses relative to HET-CTR and WT-STR females, as well as HET-STR males. In contrast, HET-STR males were less anxious than HET-CTR and WT-STR males. Reduced SERT expression is linked to more social investigation alongside increased anxiety, particularly in SERT+/- females. While cumulative ELS did not induce robust anxiety-like and depressive-like phenotypes, overall, it impaired memory performance, an effect partially mitigated in SERT+/- rats. Notably, the SERT genotype differentially modulated anxiety-like behavior in male versus female offspring, increasing vulnerability in SERT+/- females while reducing it in SERT+/- males, an effect further amplified by exposure to cumulative ELS. These results underscore sex as a critical determinant in the interaction between genetic susceptibility and cumulative exposure to early adversity in shaping affective outcomes.

Early life adversity (ELA) is a leading preventable contributor to morbidity and mortality, increasing risk for mental and physical illness later in life. However, mechanisms linking ELA to comorbid outcomes within both the brain and body remain poorly understood. We tested whether ELA disrupts functional and molecular development of vagal circuitry, a key pathway for brain-body communication, using the limited bedding and nesting (LBN) mouse model of unpredictable maternal care. We measured vagally mediated autonomic stress responses longitudinally using three noninvasive measures of heart rate variability (HRV). This is the first time the development of the vagally-mediated autonomic stress response has been measured in mice. We also performed single-nucleus RNA sequencing of the vagal medulla immediately after LBN and in adulthood, followed by spatial mapping of high-confidence differentially expressed genes. ELA altered trajectories of all HRV measures, with pronounced sex differences. ELA females showed precocious maturation followed by adult declines, whereas males initially exhibited blunted responses but recovered to control levels. Transcriptomic changes were also sex dependent, with female neurons exhibiting signatures of mitochondrial dysfunction, while males showed adaptive mitochondrial responses. Spatial mapping revealed rostro-caudal organization, localizing adaptive male responses to the rostral and intermediate vagal medulla and maladaptive female responses to the intermediate vagal medulla and loose nucleus ambiguus. These findings demonstrate enduring, sex-specific alterations in vagal circuit development centered on mitochondrial pathways.

Menopause is a major neuroendocrine transition characterised by substantial changes in endocrine milieu, physiological, psychological, and psychosexual health. Although menopausal symptoms are common, their range and severity vary considerably between individuals, suggesting that menopause is a multifaceted process. Endocrine markers (luteinising, follicle-stimulating & anti-Mullerian hormone), together with perceived well-being, may contribute to this variability. Thus, the aim was to capture the complex impact of endocrine and well-being markers on psychosexual health and menopausal symptoms. Therefore, we first applied principal component analyses to identify individual endocrine and well-being profiles, to then assess their association with psychosexual health and menopausal symptoms in pre- and post-menopausal females. Post- compared to pre-menopausal females report reduced psychosexual health and greater urogenital and psychological menopausal symptom burden. Endocrine and well-being profiles interact with reproductive status: Post-menopausal females with lower subjective well-being and a stronger menopause-like endocrine milieu report decreased overall psychosexual health and more sexual related pain. Additionally, endocrine milieu interacted with reproductive status on urogenital symptoms: Post-menopausal females with a stronger menopause-like endocrine milieu report less urogenital symptoms. Together, these findings suggest that endocrine factors and subjective well-being jointly influence psychosexual health and menopausal symptoms after menopause. No association is seen before menopause. Therefore, females after menopause need to be considered separately in research and clinic. Multivariate analyses capture patterns that are not identified using individual biomarkers and conventional univariate approaches. Our findings highlight the value of integrative multivariate approaches for improving the assessment of menopausal health and characterising individual variability across the menopausal transition.