Sex differences in the regulation of social and anxiety-related behaviors: insights from vasopressin and oxytocin brain systems

Vasopressin regulates social play behavior in sex-specific ways through glutamate modulation in the lateral septum

Understanding the neural basis of social play in juvenile rats may ultimately help restore social play deficits in autistic children. We previously found that administration of a vasopressin (AVP) V1a receptor (V1aR) antagonist into the lateral septum (LS) increased social play behavior in male juvenile rats and decreased it in females. Here, we demonstrate that glutamate, but not GABA, is involved in this sex-specific regulation. First, we found a sex difference in extracellular LS glutamate/GABA ratio (lower in females) that was eliminated by V1aR antagonist infusion in the LS that caused an increase in glutamate release in females only. Second, infusion of the glutamate receptor agonist L-glutamic acid into the LS mimicked the V1aR antagonist-induced decrease in female social play while preventing the increase in male social play. Third, infusion of the glutamate receptor antagonists AP-5 and CNQX into the LS prevented the V1aR antagonist-induced decrease in female social play. Fourth, there were no sex differences in extracellular GABA release in the LS upon either V1aR antagonist infusion or in social play expression upon infusion of the GABA-A receptor agonist muscimol into the LS, suggesting that GABA is not involved in the sex-specific regulation of social play by the LS-AVP system. Last, we found no sex differences in the type (GAD1/2, somatostatin, calbindin 1, Sox9) of V1aR-expressing LS cells, suggesting other cellular mechanisms mediating the sex-specific effects on glutamate release in the LS by the LS-AVP system. In conclusion, we demonstrate that the LS-AVP system regulates social play sex-specifically via glutamatergic neurotransmission. These findings have relevance for potential sex-specific effects of AVP-based treatment of social deficits in children.

Altered vocal communication in adult vasopressin-deficient Brattleboro rats

The neuropeptide, arginine vasopressin (AVP), has been implicated in social communication across a diverse array of species. Many rodents communicate basic behavioral states with negative versus positive valence through high-pitched vocalizations above the human hearing range (ultrasonic vocalizations; USVs). Previous studies have found that Brattleboro (Bratt) rats, which have a mutation in the Avp gene, exhibit deficits in their USVs from the early postnatal period through adolescence, but the magnitude of this effect appears to decrease from the juvenile to adolescent phase. The present study tested whether Bratt rats continue to exhibit USV deficits in adulthood. USVs of adult male and female Bratt and wild type (WT) rats were recorded in two contexts: a novel environment (empty arena) and a social context (arena filled with bedding soiled by same-sex conspecifics). The number, frequency, and duration of 50 kHz USVs were quantified by DeepSqueak after validation with manual scoring. Twenty-two kHz measures were quantified by manual scoring because DeepSqueak failed to accurately detect USVs in this frequency range. Adult Bratt rats did not exhibit deficits in the number of 50 kHz USVs: male Bratt rats emitted similar 50 kHz USVs as male WT rats, whereas female Bratt rats emitted more USVs than female WT rats. USV frequency and duration were altered in adult Bratt rats, but in a context-dependent manner. Twenty-two kHz USVs were less affected by the Bratt mutation. The present study demonstrates how chronic AVP deficiency impacts social communication across the lifespan. The present findings reveal a complex role for AVP in vocal communication, whereby disruption to the Avp gene leads to sex-, context-, and developmental phase-specific effects on the quantity and spectrotemporal characteristics of rat USVs.

Like sisters but not twins - vasopressin and oxytocin excite BNST neurons via cell type-specific expression of oxytocin receptor to reduce anxious arousal

Interoceptive signals dynamically interact with the environment to shape appropriate defensive behaviors. Hypothalamic hormones arginine-vasopressin (AVP) and oxytocin (OT) regulate physiological states, including water and electrolyte balance, circadian rhythmicity, and defensive behaviors. Both AVP and OT neurons project to dorsolateral bed nucleus of stria terminalis (BNST DL ), which expresses oxytocin receptors (OTRs) and vasopressin receptors and mediates fear responses. However, understanding the integrated role of neurohypophysial hormones is complicated by the cross-reactivity of AVP and OT and their mutual receptor promiscuity. Here, we provide evidence that the effects of neurohypophysial hormones on BNST DL excitability are driven by input specificity and cell type-specific receptor selectivity. We show that OTR-expressing BNST DL neurons, excited by hypothalamic OT and AVP inputs, play a major role in regulating BNST DL excitability, overcoming threat avoidance, and reducing threat-elicited anxious arousal. Therefore, OTR-BNST DL neurons are perfectly suited to drive the dynamic interactions balancing external threat risk and physiological needs.

Graphical abstract

Highlights

Exogenous and light-evoked vasopressin peptide excites neurons of the bed nucleus of the stria terminalis (BNST) via oxytocin receptor (OTR) in male ratsThe dorsolateral BNST receives vasopressinergic inputs from suprachiasmatic, supraoptic, and paraventricular nuclei of the hypothalamus The majority of OTR- and Corticotropin-releasing factor (CRF) neurons of the BNST are classified as Type III neurons of the BNST DL and are excited by AVP OTR-expressing BNST neurons increase exploration of open spaces and reduce anxious arousal in fear-potentiated startle in male ratsInternal signal-sensitive hypothalamic inputs directly impact BNST excitability via OTR to balance interoceptive signals and defensive behaviors.

Sex-specific effects on elements of the social brain neural network in Wistar rats from perinatal exposure to FireMaster 550 or its components

Developmental exposure to chemical flame retardants (FRs) has been linked to a variety of neurodevelopmental disorders and abnormal socioemotional behaviors in human and laboratory animal studies. We have previously shown in Wistar rats that gestational and lactational exposure to the FR mixture Firemaster 550 (FM 550) or its brominated or organophosphate ester (OPFR) components (at 2000 µg, 1000 µg, and 1000 µg oral to the dam respectively (absolute and not by bodyweight)) results in increased anxiety-like behaviors in females and decreased sociality in both sexes. Using their siblings, this study characterized sex and chemical specific targets of disruption in brain regions underlying each behavioral phenotype. Offspring were exposed across gestation and lactation then prepared for either immunohistochemistry or autoradiography at postnatal day 90 to quantify expression of serotonin, estrogen receptor α (ERα), and oxytocin receptor (OTR) in multiple brain regions. No effect of exposure was found in males for any biological target. In females, serotonin innervation was increased in the medial amygdala of FM 550 exposed animals while ERα expression in the bed nucleus of the stria terminalis (BNST) was reduced by FM 550 and OPFR. Evidence of disrupted OTR was observed in males, particularly the BNST but considered an exploratory finding given the small sample size. These results begin to shed light on the mechanisms by which developmental FR exposure alters socioemotional behaviors of relevance to neurodevelopmental disorders.

The interplay of oxytocin and sex hormones

The neuropeptide oxytocin has historically been associated with reproduction and maternal behavior. However, more recent research has uncovered that oxytocin has a much wider range of roles in physiology and behavior. Despite the excitement surrounding potential therapeutical applications of intranasally administered oxytocin, the results of these intervention studies have been inconsistent. Various reasons for these mixed results have been proposed, which tend to focus on methodological issues, such as study design. While methodological issues are certainly important, emerging evidence suggests that the interaction between oxytocin and sex hormones may also account for these varied findings. To better understand the purpose and function of the interaction of oxytocin with sex hormones, with a focus on estrogens, progesterone, and testosterone, we conducted a comprehensive thematic review via four perspectives: evolutionary, developmental, mechanistic, and survival. Altogether, this synergistic approach highlights the critical function of sex hormone activity for accomplishing the diverse roles of oxytocin via the modulation of oxytocin release and oxytocin receptor activity, which is also likely to contribute to the heterogeneity of outcomes after oxytocin administration.

Effect of lateral septum vasopressin administration on reward system neurochemistry and amphetamine-induced addictive-like behaviors in female rats

Introduction: The chronic use of psychostimulants increases the risk of addiction and, there is no specific pharmacologic treatment for psychostimulant addiction. The vasopressin (AVP) system is a possible pharmacological target in drug addiction. Previous results obtained in our laboratory showed that amphetamine (AMPH) treatment decreases lateral septum (LS) AVP levels in male rats, and AVP microinjection in LS decreases addictive-like behavior. The aim of the present work was to investigate the effect of AMPH treatment on LS AVP levels and the effect of LS AVP administration on the expression of AMPH-conditioned place preference (CPP) in female rats. The secondary objectives were to study the effect of LS AVP administration on LS GABA and glutamate release in male and female rats and on nucleus accumbens (NAc) dopamine (DA) release in female rats. Methods: Female rats were conditioned with AMPH (1.5 mg/kg i.p.) or saline for 4 days. Results: Conditioning with AMPH did not change LS AVP content in females. However, AVP microinjection into the LS decreased the expression of conditioned place preference (CPP) to AMPH. Glutamate and GABA extracellular levels in the LS induced by AVP were studied in males and females. NAc GABA and DA extracellular levels induced by LS AVP microinjection in female rats were measured by microdialysis. In males, AVP perfusion produced a significant increase in LS GABA extracellular levels; however, a decrease in GABA extracellular levels was observed in females. Both in males and females, LS AVP perfusion did not produce changes in LS glutamate extracellular levels. Microinjection of AVP into the LS did not change GABA or DA extracellular levels in the NAc of females. Discussion: Therefore, AVP administration into the LS produces different LS-NAc neurochemical responses in females than males but decreases CPP to AMPH in both sexes. The behavioral response in males is due to a decrease in NAc DA levels, but in females, it could be due to a preventive increase in NAc DA levels. It is reasonable to postulate that, in females, the decrease in conditioning produced by AVP microinjection is influenced by other factors inherent to sex, and an effect on anxiety cannot be discarded.

A Transcriptomic Dataset of Embryonic Murine Telencephalon

Sex bias is known in the prevalence/pathology of neurodevelopmental disorders. Sex-dependent differences of the certain brain areas are known to emerge perinatally through the exposure to sex hormones, while gene expression patterns in the rodent embryonic brain does not seem to be completely the same between male and female. To investigate potential sex differences in gene expression and cortical organization during the embryonic period in mice, we conducted a comprehensive analysis of gene expression for the telencephalon at embryonic day (E) 11.5 (a peak of neural stem cell expansion) and E14.5 (a peak of neurogenesis) using bulk RNA-seq data. As a result, our data showed the existence of notable sex differences in gene expression patterns not obviously at E11.5, but clearly at E14.5 when neurogenesis has become its peak. These data can be useful for exploring potential contribution of genes exhibiting sex differences to the divergence in brain development. Additionally, our data underscore the significance of studying the embryonic period to gain a deeper understanding of sex differences in brain development.

Effect of chronic administration of ostruthin on depression-like behavior in chronically stressed mice

We have previously shown that a single dose of a TREK-1 channel activator, ostruthin, exhibited antidepressant and anxiolytic effects in acute behavioral test models in mice. To assess the potential clinical application, it is essential to evaluate the effects of long-term administration of ostruthin in a chronically stressed mouse model, which is considered to be similar to the clinical condition of major depression in humans. Here, we tested the effects of a single and a 7-day administration of ostruthin on mice that were subjected to chronic unpredictable mild stress (CUMS). A single administration of ostruthin showed antidepressive effects in the tail suspension and forced swim tests of CUMS-treated mice. Unexpectedly, the 7-day administration exhibited only insignificant antidepressive and anxiolytic effects. The 7-day regimen did not affect food intake or body-weight gain, suggesting the absence of apparent cytotoxicity. The mice receiving the 7-day administration had significantly lower blood concentrations of ostruthin compared to those receiving a single dose, suggesting an upregulation of drug-metabolizing activities. These findings suggest that there is a need for stable TREK-1 channel activators that are not affected by drug metabolism.

Effects of arginine vasopressin on human anxiety and associations with sex, dose, and V1a-receptor genotype

RATIONALE

Arginine vasopressin (AVP) has dose- and sex-specific effects on social behavior, and variation in social responses is related to variation in the V1a receptor gene in animals. Whether such complexity also characterizes AVP effects on anxiety in humans, or whether V1a genotype is related to anxiety and/or AVP's ability to affect it, remains to be determined.

OBJECTIVE

To test if AVP has dose-dependent effects on anxiety in men and/or women and if a particular allele within the RS3 promoter region of the V1a receptor gene is associated with anxiety and/or AVP effects on anxiety.

METHOD

Men and women self-administered 20 IU or 40 IU intranasal arginine vasopressin (AVP) and placebo in a double-blind, within-subjects design, and State (SA) and Trait (TA) anxiety were measured 60 min later. PCR was used to identify allelic variation within the RS3 region of the V1a receptor gene.

RESULTS

AVP decreased SA in men across both doses, whereas only the lower dose had the same effect, across sexes, in individuals who carry at least one copy of a previously identified "risk" allele in the RS3 promoter of the V1a receptor gene. Additionally, after placebo, women who carried a copy of the allele displayed lower TA than women who did not, and AVP acutely increased TA scores in those women.

CONCLUSIONS

Exogenous AVP has modest sex- and dose-dependent effects on anxiety/affect in humans. Further, allelic variation in the V1a promoter appears associated with responsiveness to AVP's effects and, at least in women, to stable levels of anxiety/affect.

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.

Beyond the binary: Characterizing the relationships between sex and neuropeptide receptor binding density measures in the rat brain

Sex differences exist in numerous parameters of the brain. Yet, sex-related factors are part of a large set of variables that interact to affect many aspects of brain structure and function. This raises questions regarding how to interpret findings of sex differences at the level of single brain measures and the brain as a whole. In the present study, we reanalyzed two datasets consisting of measures of oxytocin, vasopressin V1a, and mu opioid receptor binding densities in multiple brain regions in rats. At the level of single brain measures, we found that sex differences were rarely dimorphic and were largely persistent across estrous stage and parental status but not across age or context. At the level of aggregates of brain measures showing sex differences, we tested whether individual brains are 'mosaics' of female-typical and male-typical measures or are internally consistent, having either only female-typical or only male-typical measures. We found mosaicism for measures showing overlap between females and males. Mosaicism was higher a) with a larger number of measures, b) with smaller effect sizes of the sex difference in these measures, and c) in rats with more diverse life experiences. Together, these results highlight the limitations of the binary framework for interpreting sex effects on the brain and suggest two complementary pathways to studying the contribution of sex to brain function: (1) focusing on measures showing dimorphic and persistent sex differences and (2) exploring the relations between specific brain mosaics and specific endpoints.

Early life adversity reduces affiliative behavior with a stressed cagemate and leads to sex-specific alterations in corticosterone responses in adult mice

Experiencing early life adversity (ELA) alters stress physiology and increases the risk for developing psychiatric disorders. The social environment can influence dynamics of stress responding and buffer and/or transfer stress across individuals. Yet, the impact of ELA on sensitivity to the stress of others and social behavior following stress is unknown. Here, to test the impact of ELA on social and physiological responses to stress, circulating blood corticosterone (CORT) and social behaviors were assessed in adult male and female mice reared under limited bedding and nesting (LBN) or control conditions. To induce stress, one cagemate of a pair-housed cage underwent a footshock paradigm and was then returned to their unshocked partner. CORT was measured in both groups of mice 20 or 90 min after stress exposure, and social behaviors were recorded and analyzed. ELA rearing influenced the CORT response to stress in a sex-specific manner. In males, both control and ELA-reared mice exhibited similar stress transfer to unshocked cagemates and similar CORT dynamics. In contrast, ELA females showed a heightened stress transfer to unshocked cagemates, and sustained elevation of CORT relative to controls, indicating enhanced stress contagion and a failure to terminate the stress response. Behaviorally, ELA females displayed decreased allogrooming and increased investigative behaviors, while ELA males showed reduced huddling. Together, these findings demonstrate that ELA influenced HPA axis dynamics, social stress contagion and social behavior. Further research is needed to unravel the underlying mechanisms and long-term consequences of ELA on stress systems and their impact on behavioral outcomes.

Male rat hypothalamic extraretinal photoreceptor Opsin3 is sensitive to osmotic stimuli and light

The light-sensitive protein Opsin 3 (Opn3) is present throughout the mammalian brain; however, the role of Opn3 in this organ remains unknown. Since Opn3 encoded mRNA is modulated in the supraoptic and paraventricular nucleus of the hypothalamus in response to osmotic stimuli, we have explored by in situ hybridization the expression of Opn3 in these nuclei. We have demonstrated that Opn3 is present in the male rat magnocellular neurones expressing either the arginine vasopressin or oxytocin neuropeptides and that Opn3 increases in both neuronal types in response to osmotic stimuli, suggesting that Opn3 functions in both cell types and that it might be involved in regulating water balance. Using rat hypothalamic organotypic cultures, we have demonstrated that the hypothalamus is sensitive to light and that the observed light sensitivity is mediated, at least in part, by Opn3. The data suggests that hypothalamic Opn3 can mediate a light-sensitive role to regulate circadian homeostatic processes.

Social anxiety disorder-associated gut microbiota increases social fear

Social anxiety disorder (SAD) is a crippling psychiatric disorder characterized by intense fear or anxiety in social situations and their avoidance. However, the underlying biology of SAD is unclear and better treatments are needed. Recently, the gut microbiota has emerged as a key regulator of both brain and behaviour, especially those related to social function. Moreover, increasing data supports a role for immune function and oxytocin signalling in social responses. To investigate whether the gut microbiota plays a causal role in modulating behaviours relevant to SAD, we transplanted the microbiota from SAD patients, which was identified by 16S rRNA sequencing to be of a differential composition compared to healthy controls, to mice. Although the mice that received the SAD microbiota had normal behaviours across a battery of tests designed to assess depression and general anxiety-like behaviours, they had a specific heightened sensitivity to social fear, a model of SAD. This distinct heightened social fear response was coupled with changes in central and peripheral immune function and oxytocin expression in the bed nucleus of the stria terminalis. This work demonstrates an interkingdom basis for social fear responses and posits the microbiome as a potential therapeutic target for SAD.

Prenatal allergic inflammation in rats confers sex-specific alterations to oxytocin and vasopressin innervation in social brain regions

Prenatal exposure to inflammation via maternal infection, allergy, or autoimmunity increases one's risk for developing neurodevelopmental and psychiatric disorders. Many of these disorders are associated with altered social behavior, yet the mechanisms underlying inflammation-induced social impairment remain unknown. We previously found that a rat model of acute allergic maternal immune activation (MIA) produced deficits like those found in MIA-linked disorders, including impairments in juvenile social play behavior. The neuropeptides oxytocin (OT) and arginine vasopressin (AVP) regulate social behavior, including juvenile social play, across mammalian species. OT and AVP are also implicated in neuropsychiatric disorders characterized by social impairment, making them good candidate regulators of social deficits after MIA. We profiled how acute prenatal exposure to allergic MIA changed OT and AVP innervation in several brain regions important for social behavior in juvenile male and female rat offspring. We also assessed whether MIA altered additional behavioral phenotypes related to sociality and anxiety. We found that allergic MIA increased OT and AVP fiber immunoreactivity in the medial amygdala and had sex-specific effects in the nucleus accumbens, bed nucleus of the stria terminalis, and lateral hypothalamic area. We also found that MIA reduced ultrasonic vocalizations in neonates and increased the stereotypical nature of self-grooming behavior. Overall, these findings suggest that there may be sex-specific mechanisms underlying MIA-induced behavioral impairment and underscore OT and AVP as ideal candidates for future mechanistic studies.

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.

Determining the neuronal ensembles underlying sex-specific social impairments following adolescent intermittent ethanol exposure

Binge drinking during adolescence can have behavioral and neurobiological consequences. We have previously found that adolescent intermittent ethanol (AIE) exposure produces sex-specific social alterations indexed via decreases of social investigation and/or social preference in rats. The prelimbic cortex (PrL) regulates social interaction, and alterations within the PrL resulting from AIE may contribute to social alterations. The current study sought to determine whether AIE-induced PrL dysfunction underlies decreases in social interaction evident in adulthood. We first examined social interaction-induced neuronal activation of the PrL and several other regions of interest (ROIs) implicated in social interaction. Adolescent male and female cFos-LacZ rats were exposed to water (control) or ethanol (4 g/kg, 25% v/v) via intragastric gavage every other day between postnatal day (P) 25 and 45 (total 11 exposures). Since cFos-LacZ rats express β-galactosidase (β-gal) as a proxy for Fos, activated cells that express of β-gal can be inactivated by Daun02. In most ROIs, expression of β-gal was elevated in socially tested adult rats relative to home cage controls, regardless of sex. However, decreased social interaction-induced β-gal expression in AIE-exposed rats relative to controls was evident only in the PrL of males. A separate cohort underwent PrL cannulation surgery in adulthood and was subjected to Daun02-induced inactivation. Inactivation of PrL ensembles previously activated by social interaction reduced social investigation in control males, with no changes evident in AIE-exposed males or females. These findings highlight the role of the PrL in male social investigation and suggest an AIE-associated dysfunction of the PrL that may contribute to reduced social investigation following adolescent ethanol exposure.

Social Interaction Is Less Rewarding in Adult Female than in Male Mice

(1) Background: Positive social relationships are essential for mental and physical health. However, not all individuals experience social interaction as a rewarding activity. (2) Methods: Social interaction reward in mice can be assessed by social conditioned place preference (CPP). The aim of this study is to investigate sex-dependent differences in the neurological underpinnings underlying social versus non-social phenotypes, using adult male and female C57BL/6J mice. (3) Results: Adult female mice expressed significantly less social reward than males from the same strain. Accordingly, pairs of male mice spent more time interacting as compared to female pairs. Subsequently, we analyzed neuropeptides previously reported to be important regulators of social behavior such as oxytocin, vasopressin, and orexin, in addition to Ca2+/calmodulin-dependent protein kinase II (αCaMKII), shown to be involved in social reward. Levels of neuropeptides and αCaMKII were comparable between males and females in all investigated regions. Yet, a significant negative correlation was found between endogenous oxytocin expression and social reward in female pairs. (4) Conclusions: Sex differences in the prevalence of many mental health disorders might at least in part be due to sex differences in social reward. Therefore, more research is needed to unravel the candidate(s) underlying this behavioral difference.

Four-week intranasal oxytocin administration reduces attachment avoidance in older women

The neuropeptide oxytocin (OT) serves as a critical modulator of social cognition and social behavior. Adult attachment is an affiliative process crucial for social interaction across adulthood. Insecure adult attachment comprises two broad dimensions, attachment anxiety and attachment avoidance. Both these dimensions of attachment are currently understudied regarding OT modulation, and especially in older adults. The present study determined the effects of chronic intranasal OT administration on adult attachment in generally healthy older women and men (aged 55-95 years). Embedded in a larger project, participants were randomly assigned to self-administer 24 international units of either OT or a placebo (P) intranasally twice daily for four weeks. The Experiences in Close Relationships Scale assessed adult attachment (anxiety and avoidance) pre- and post-treatment. There was no significant pre- to post-treatment change in attachment avoidance overall, but the treatment x timepoint x sex interaction was significant, in that women (but not men) in the OT (vs. P) group reported decreased attachment avoidance. No comparable effects were observed for attachment anxiety. Results suggest that older women may benefit from chronic intranasal OT treatment by experiencing less attachment avoidance in their adult relationships.

Sex differences in resting-state functional networks in awake rats

Sex-related differences can be found in many brain disorders and psychophysiological traits, highlighting the importance to systematically understand the sex differences in brain function in humans and animal models. Despite emerging effort to address sex differences in behaviors and disease models in rodents, how brain-wide functional connectivity (FC) patterns differ between male and female rats remains largely unknown. Here, we used resting-state functional magnetic resonance imaging (rsfMRI) to investigate regional and systems-level differences between female and male rats. Our data show that female rats display stronger hypothalamus connectivity, whereas male rats exhibit more prominent striatum-related connectivity. At the global scale, female rats demonstrate stronger segregation within the cortical and subcortical systems, while male rats display more prominent cortico-subcortical interactions, particularly between the cortex and striatum. Taken together, these data provide a comprehensive framework of sex differences in resting-state connectivity patterns in the awake rat brain, and offer a reference for studies aiming to reveal sex-related FC differences in different animal models of brain disorders.

Perinatal opioid exposure leads to decreased social play in adolescent male and female rats: Potential role of oxytocin signaling in brain regions associated with social reward

Over the last two decades, the number of infants exposed to opioids in utero has quadrupled in the United States, with some states reporting rates as high as 55 infants per 1000 births. Clinical studies report that children previously exposed to opioids during gestation show significant deficits in social behavior, including an inability to form friendships or other social relationships. To date, the neural mechanisms whereby developmental opioid exposure disrupts social behavior remain unknown. Using a novel paradigm of perinatal opioid administration, we tested the hypothesis that chronic opioid exposure during critical developmental periods would disrupt juvenile play. As oxytocin is a major regulator of sociability, the impact of perinatal morphine exposure on oxytocin peptide expression was also examined. Juvenile play was assessed in vehicle- or morphine-exposed male and female rats at P25, P35, and P45. Classical features of juvenile play were measured, including time spent engaged in social play, time not in contact, number of pins, and number of nape attacks. We report that morphine-exposed males and females spend less time engaged in play behavior than control males and females, with a corresponding increase in time spent alone. Morphine-exposed males and females also initiated fewer pins and nape attacks. Together, these data suggest that male and female rats exposed to morphine during critical developmental periods are less motivated to participate in social play, potentially due to alterations in oxytocin-mediated reward signaling.

Perturbation of maternal gut microbiota in mice during a critical perinatal window influences early neurobehavioral outcomes in offspring

The gut microbiota is increasingly recognized as a key environmental factor that shapes host development and physiology, including neural circuits formation and function. Concurrently, there has been growing concern that early-life antibiotic exposure may alter brain developmental trajectories, increasing the risk for neurodevelopmental disorders such as autism spectrum disorder (ASD). Here, we assessed whether perturbation of the maternal gut microbiota in mice during a narrow critical perinatal window (last week of pregnancy and first three postnatal days), induced by exposure to a commonly used broad-spectrum oral antibiotic (ampicillin), influences offspring neurobehavioral outcomes relevant to ASD. Our results demonstrate that neonatal offspring from antibiotic-treated dams display an altered pattern of ultrasonic communication, which was more pronounced in males. Moreover, juvenile male, but not female, offspring from antibiotic-treated dams showed reduced social motivation and social interaction, as well as context-dependent anxiety-like behavior. However, no changes were observed in locomotor or exploratory activity. This behavioral phenotype of exposed juvenile males was associated with reduced gene expression of the oxytocin receptor (OXTR) and several tight-junction proteins in the prefrontal cortex, a key region involved in the regulation of social and emotional behaviors, as well as a mild inflammatory response in the colon. Further, juvenile offspring from exposed dams also showed distinct alterations in several gut bacterial species, including, Lactobacillus murinus, and Parabacteroides goldsteinii. Overall, this study highlights the importance of the maternal microbiome in early-life, and how its perturbation by a widely used antibiotic could contribute to atypical social and emotional development of offspring in a sex-dependent manner.

Male-selective effects of oxytocin agonism on alcohol intake: behavioral assessment in socially housed prairie voles and involvement of RAGE

Targeting the oxytocin (OXT) peptide system has emerged as a promising new approach for the treatment of alcohol use disorder (AUD). However, further advancements in this development depend on properly modeling various complex social aspects of AUD and its treatment. Here we examined behavioral and molecular underpinnings of OXT receptor (OXTR) agonism in prairie voles, a rodent species with demonstrated translational validity for neurobiological mechanisms regulating social affiliations. To further improve translational validity of these studies, we examined effects of intranasal (IN) OXT administration in male and female prairie voles socially housed in the presence of untreated cagemates. IN OXT selectively inhibited alcohol drinking in male, but not female, animals. Further, we confirmed that exogenously administered OXT penetrates the prairie vole brain and showed that Receptor for Advanced Glycation End-products assists this penetration after IN, but not intraperitoneal (IP), OXT administration. Finally, we demonstrated that IP administration of LIT-001, a small-molecule OXTR agonist, inhibits alcohol intake in male, but not female, prairie voles socially housed in the presence of untreated cagemates. Taken together, results of this study support the promise of selectively targeting OXTR for individualized treatment of AUD.

Acute intranasal oxytocin dose enhances social preference for parents over peers in male but not female peri-adolescent California mice (Peromyscus californicus)

Peri-adolescence is a critical developmental stage marked by profound changes in the valence of social interactions with parents and peers. We hypothesized that the oxytocin (OXT) and vasopressin (AVP) systems, known for influencing social behavior, would be involved in the maintenance and breaking of bonding behavior expressed by very early peri-adolescent males and females. In rodents, OXT is associated with mother-pup bonding and may promote social attachment to members of the natal territory. AVP, on the other hand, can act in contrasting ways to OXT and has been associated with aggression and territoriality. Specifically, we predicted that in peri-adolescent male and female juveniles of the biparental and territorial California mouse (Peromyscus californicus), a) OXT would increase the social preferences for the parents over unfamiliar age-matched peers (one male and one female), and b) AVP would break the parent-offspring bond and either increase time in the neutral chamber and/or approach to their unfamiliar and novel peers. We examined anxiety and exploratory behavior using an elevated plus maze and a novel object task as a control. Peri-adolescent mice were administered an acute intranasal (IN) treatment of 0.5 IU/kg IN AVP, 0.5 IU/kg IN OXT, or saline control; five minutes later, the behavioral tests were conducted. As predicted, we found that IN OXT enhanced social preference for parents; however, this was only in male and not female peri-adolescent mice. IN AVP did not influence social preference in either sex. These effects appear specific to social behavior and not anxiety, as neither IN OXT nor AVP influenced behavior during the elevated plus maze or novel object tasks. To our knowledge, this is the first evidence indicating that OXT may play a role in promoting peri-adolescent social preferences for parents and delaying weaning in males.

The role of androgens and estrogens in social interactions and social cognition

Gonadal hormones are becoming increasingly recognized for their effects on cognition. Estrogens, in particular, have received attention for their effects on learning and memory that rely upon the functioning of various brain regions. However, the impacts of androgens on cognition are relatively under investigated. Testosterone, as well as estrogens, have been shown to play a role in the modulation of different aspects of social cognition. This review explores the impact of testosterone and other androgens on various facets of social cognition including social recognition, social learning, social approach/avoidance, and aggression. We highlight the relevance of considering not only the actions of the most commonly studied steroids (i.e., testosterone, 17β-estradiol, and dihydrotestosterone), but also that of their metabolites and precursors, which interact with a plethora of different receptors and signalling molecules, ultimately modulating behaviour. We point out that it is also essential to investigate the effects of androgens, their precursors and metabolites in females, as prior studies have mostly focused on males. Overall, a comprehensive analysis of the impact of steroids such as androgens on behaviour is fundamental for a full understanding of the neural mechanisms underlying social cognition, including that of humans.

“The two voices,” or more? Music and gender from myth and conquests to the neurosciences

Music is a unique phenomenon, constantly eliciting interest from a variety of viewpoints, several of which intersect the universal trait of musicality with sex/gender studies and the neurosciences. Its unparalleled power and physical, social, aesthetic, as well as cognitive, emotional and clinical ramifications make it a specially promising terrain for studies and reflections on sex and gender differences and their impact. This overview wishes to enhance awareness of such issues, also fostering an interdisciplinary exchange between the natural sciences, the humanities, and the arts. Over the centuries, different associations of music with the feminine gender have contributed to a pendulum between progressive recognition and stereotypical setbacks requiring to be overcome. Against this backdrop, music-related neurophysiological and psychological studies on sex and gender specificities are reviewed in their multiple approaches and results, exposing or questioning differences in structural, auditory, hormonal, cognitive, and behavioral areas, also in relation to abilities, treatment, and pedagogy. Thus, the bridging potential of music as universal yet diverse language, art, and practice, recommends its gender-aware integration into education, protective endeavors, and therapeutic interventions, to promote equality and well-being.

Determining the neuronal ensembles underlying sex-specific social impairments following adolescent intermittent ethanol exposure

Binge drinking during adolescence can have behavioral and neurobiological consequences. We have previously found that adolescent intermittent ethanol (AIE) exposure produces a sex-specific social impairment in rats. The prelimbic cortex (PrL) regulates social behavior, and alterations within the PrL resulting from AIE may contribute to social impairments. The current study sought to determine whether AIE-induced PrL dysfunction underlies social deficits in adulthood. We first examined social stimulus-induced neuronal activation of the PrL and several other regions of interest implicated in social behavior. Male and female cFos-LacZ rats were exposed to water (control) or ethanol (4 g/kg, 25% v/v) via intragastric gavage every other day between postnatal day (P) 25 and 45 (total 11 exposures). Since cFos-LacZ rats express β-galactosidase (β-gal) as a proxy for cFos, activated cells that express of β-gal can be inactivated by Daun02. β-gal expression in most ROIs was elevated in socially tested adult rats relative to home cage controls, regardless of sex. However, differences in social stimulus-induced β-gal expression between controls and AIE-exposed rats was evident only in the PrL of males. A separate cohort underwent PrL cannulation surgery in adulthood and were subjected to Daun02-induced inactivation. Inactivation of PrL ensembles previously activated by a social stimulus led to a reduction of social behavior in control males, with no changes evident in AIE-exposed males or females. These findings highlight the role of the PrL in male social behavior and suggest an AIE-associated dysfunction of the PrL may contribute to social deficits following adolescent ethanol exposure.

Sex differences in resting-state functional networks in awake rats

Sex-related differences can be found in many brain disorders and psychophysiological traits, highlighting the importance to systematically understand the sex differences in brain function in humans and animal models. Despite emerging effort to address sex differences in behaviors and disease models in rodents, how brain-wide functional connectivity (FC) patterns differ between male and female rats remains largely unknown. Here we used resting-state functional magnetic resonance imaging (rsfMRI) to investigate regional and systems-level differences between female and male rats. Our data show that female rats display stronger hypothalamus connectivity, whereas male rats exhibit more prominent striatum-related connectivity. At the global scale, female rats demonstrate stronger segregation within the cortical and subcortical systems, while male rats display more prominent cortico-subcortical interactions, particularly between the cortex and striatum. Taken together, these data provide a comprehensive framework of sex differences in resting-state connectivity patterns in the awake rat brain, and offer a reference for studies aiming to reveal sex-related FC differences in different animal models of brain disorders.

Alleviating anxiety and taming trauma: Novel pharmacotherapeutics for anxiety disorders and posttraumatic stress disorder

Psychiatric disorders associated with psychological trauma, stress and anxiety are a highly prevalent and increasing cause of morbidity worldwide. Current therapeutic approaches, including medication, are effective in alleviating symptoms of anxiety disorders and posttraumatic stress disorder (PTSD), at least in some individuals, but have unwanted side-effects and do not resolve underlying pathophysiology. After a period of stagnation, there is renewed enthusiasm from public, academic and commercial parties in designing and developing drug treatments for these disorders. Here, we aim to provide a snapshot of the current state of this field that is written for neuropharmacologists, but also practicing clinicians and the interested lay-reader. After introducing currently available drug treatments, we summarize recent/ongoing clinical assessment of novel medicines for anxiety and PTSD, grouped according to primary neurochemical targets and their potential to produce acute and/or enduring therapeutic effects. The evaluation of putative treatments targeting monoamine (including psychedelics), GABA, glutamate, cannabinoid, cholinergic and neuropeptide systems, amongst others, are discussed. We emphasize the importance of designing and clinically assessing new medications based on a firm understanding of the underlying neurobiology stemming from the rapid advances being made in neuroscience. This includes harnessing neuroplasticity to bring about lasting beneficial changes in the brain rather than - as many current medications do - produce a transient attenuation of symptoms, as exemplified by combining psychotropic/cognitive enhancing drugs with psychotherapeutic approaches. We conclude by noting some of the other emerging trends in this promising new phase of drug development.

Oxytocin receptors in the Magel2 mouse model of autism: Specific region, age, sex and oxytocin treatment effects

The neurohormone oxytocin (OXT) has been implicated in the regulation of social behavior and is intensively investigated as a potential therapeutic treatment in neurodevelopmental disorders characterized by social deficits. In the Magel2-knockout (KO) mouse, a model of Schaaf-Yang Syndrome, an early postnatal administration of OXT rescued autistic-like behavior and cognition at adulthood, making this model relevant for understanding the actions of OXT in (re)programming postnatal brain development. The oxytocin receptor (OXTR), the main brain target of OXT, was dysregulated in the hippocampus of Magel2-KO adult males, and normalized upon OXT treatment at birth. Here we have analyzed male and female Magel2-KO brains at postnatal day 8 (P8) and at postnatal day 90 (P90), investigating age, genotype and OXT treatment effects on OXTR levels in several regions of the brain. We found that, at P8, male and female Magel2-KOs displayed a widespread, substantial, down-regulation of OXTR levels compared to wild type (WT) animals. Most intriguingly, the postnatal OXT treatment did not affect Magel2-KO OXTR levels at P8 and, consistently, did not rescue the ultrasonic vocalization deficits observed at this age. On the contrary, the postnatal OXT treatment reduced OXTR levels at P90 in male Magel2-KO in a region-specific way, restoring normal OXTR levels in regions where the Magel2-KO OXTR was upregulated (central amygdala, hippocampus and piriform cortex). Interestingly, Magel2-KO females, previously shown to lack the social deficits observed in Magel2-KO males, were characterized by a different trend in receptor expression compared to males; as a result, the dimorphic expression of OXTR observed in WT animals, with higher OXTR expression observed in females, was abolished in Magel2-KO mice. In conclusion, our data indicate that in Magel2-KO mice, OXTRs undergo region-specific modifications related to age, sex and postnatal OXT treatment. These results are instrumental to design precisely-timed OXT-based therapeutic strategies that, by acting at specific brain regions, could modify the outcome of social deficits in Schaaf-Yang Syndrome patients.

Perinatal Opioid Exposure Leads to Decreased Social Play in Adolescent Male and Female Rats: Potential Role of Oxytocin Signaling in Brain Regions Associated with Social Reward

Over the last two decades, the number of infants exposed to opioids in utero has quadrupled in the United States, with some states reporting rates as high as 55 infants per 1000 births. Clinical studies report that children previously exposed to opioids during gestation show significant deficits in social behavior, including an inability to form friendships or other social relationships. To date, the neural mechanisms whereby developmental opioid exposure disrupts social behavior remain unknown. Using a novel paradigm of perinatal opioid administration, we tested the hypothesis that chronic opioid exposure during critical developmental periods would disrupt juvenile play. As oxytocin is a major regulator of sociability, the impact of perinatal morphine exposure on oxytocin peptide and receptor expression was also examined. Juvenile play was assessed in vehicle- or morphine-exposed male and female rats at P25, P35, and P45. Classical features of juvenile play were measured, including time spent engaged in social play, time not in contact, number of pins, and number of nape attacks. We report that morphine-exposed females spend less time engaged in play behavior than control males and females, with a corresponding increase in time spent alone. Morphine-exposed females also initiated fewer pins and nape attacks. Oxytocin receptor binding was reduced in morphine-exposed females in the nucleus accumbens, a brain region critical for social reward. Together, these data suggest that females exposed to morphine during critical developmental periods are less motivated to participate in social play, potentially due to alterations in oxytocin-mediated reward signaling.

Sex Differences in Inflammation and Muscle Wasting in Aging and Disease

Only in recent years, thanks to a precision medicine-based approach, have treatments tailored to the sex of each patient emerged in clinical trials. In this regard, both striated muscle tissues present significant differences between the two sexes, which may have important consequences for diagnosis and therapy in aging and chronic illness. In fact, preservation of muscle mass in disease conditions correlates with survival; however, sex should be considered when protocols for the maintenance of muscle mass are designed. One obvious difference is that men have more muscle than women. Moreover, the two sexes differ in inflammation parameters, particularly in response to infection and disease. Therefore, unsurprisingly, men and women respond differently to therapies. In this review, we present an up-to-date overview on what is known about sex differences in skeletal muscle physiology and disfunction, such as disuse atrophy, age-related sarcopenia, and cachexia. In addition, we summarize sex differences in inflammation which may underly the aforementioned conditions because pro-inflammatory cytokines deeply affect muscle homeostasis. The comparison of these three conditions and their sex-related bases is interesting because different forms of muscle atrophy share common mechanisms; for instance, those responsible for protein dismantling are similar although differing in terms of kinetics, severity, and regulatory mechanisms. In pre-clinical research, exploring sexual dimorphism in disease conditions could highlight new efficacious treatments or recommend implementation of an existing one. Any protective factors discovered in one sex could be exploited to achieve lower morbidity, reduce the severity of the disease, or avoid mortality in the opposite sex. Thus, the understanding of sex-dependent responses to different forms of muscle atrophy and inflammation is of pivotal importance to design innovative, tailored, and efficient interventions.

Amygdala AVPR1A mediates susceptibility to chronic social isolation in females

Females are more sensitive to social exclusion, which could contribute to their heightened susceptibility to anxiety disorders. Chronic social isolation stress (CSIS) for at least 7 weeks after puberty induces anxiety-related behavioral adaptations in female mice. Here, we show that Arginine vasopressin receptor 1a ( Avpr1a )-expressing neurons in the central nucleus of the amygdala (CeA) mediate these sex-specific effects, in part, via projections to the caudate putamen. Loss of function studies demonstrate that AVPR1A signaling in the CeA is required for effects of CSIS on anxiety-related behaviors in females but has no effect in males or group housed females. This sex-specificity is mediated by AVP produced by a subpopulation of neurons in the posterodorsal medial nucleus of the amygdala that project to the CeA. Estrogen receptor alpha signaling in these neurons also contributes to preferential sensitivity of females to CSIS. These data support new therapeutic applications for AVPR1A antagonists in women.

Modulation of social behavior by distinct vasopressin sources

The neuropeptide arginine-vasopressin (AVP) is well known for its peripheral effects on blood pressure and antidiuresis. However, AVP also modulates various social and anxiety-related behaviors by its actions in the brain, often sex-specifically, with effects typically being stronger in males than in females. AVP in the nervous system originates from several distinct sources which are, in turn, regulated by different inputs and regulatory factors. Based on both direct and indirect evidence, we can begin to define the specific role of AVP cell populations in social behavior, such as, social recognition, affiliation, pair bonding, parental behavior, mate competition, aggression, and social stress. Sex differences in function may be apparent in both sexually-dimorphic structures as well as ones without prominent structural differences within the hypothalamus. The understanding of how AVP systems are organized and function may ultimately lead to better therapeutic interventions for psychiatric disorders characterized by social deficits.

The BDNF Val68Met polymorphism causes a sex specific alcohol preference over social interaction and also acute tolerance to the anxiolytic effects of alcohol, a phenotype driven by malfunction of BDNF in the ventral hippocampus of male mice

BACKGROUND

The brain-derived neurotrophic factor (BDNF) Valine 66 to Methionine human polymorphism results in impaired activity-dependent BDNF release and has been linked to psychiatric disorders including depression and anxiety. We previously showed that male knock-in mice carrying the mouse Methionine homolog (Met68BDNF) exhibit excessive and compulsive alcohol drinking behaviors as compared to the wild-type Val68BDNF mice.

OBJECTIVE

Here, we set out to determine the potential mechanism for the heightened and compulsive alcohol drinking phenotypes detected in Met68BDNF mice.

RESULTS

We found that male, but not female Met68BDNF mice exhibit social anxiety-like behaviors. We further show that male Met68BDNF mice exhibit a preference for alcohol over social interaction. In contrast, alcohol place preference without an alternative social reward, is similar in male Met68BDNF and Val68BDNF mice. Since the Met68BDNF mice show social anxiety phenotypes, we tested whether alcohol reliefs anxiety similarly in Met68BDNF and Val68BDNF mice and found that male, but not female Met68BDNF mice are insensitive to the acute anxiolytic action of alcohol. Finally, we show that this acute tolerance to alcohol-dependent anxiolysis can be restored by overexpressing wild-type Val68BDNF in the ventral hippocampus (vHC) of Met68BDNF mice.

CONCLUSIONS

Together, our results suggest that excessive alcohol drinking in the Met68BDNF may be attributed, in part, to heighted social anxiety and a lack of alcohol-dependent anxiolysis, a phenotype that is associated with malfunction of BDNF signaling in the vHC of male Met68BDNF mice.

Local CRF and oxytocin receptors correlate with female experience-driven avoidance change and hippocampal neuronal plasticity

Understanding how experiences affect females' behaviors and neuronal plasticity is essential for uncovering the mechanism of neurodevelopmental disorders. The study explored how neonatal maternal deprivation (MD) and post-weaning environmental enrichment (EE) impacted the CA1 and DG's neuronal plasticity in the dorsal hippocampus, and its relationships with passive avoidance, local corticotrophin-releasing factor (CRF) levels, and oxytocin receptor (OTR) levels in female BALB/c mice. The results showed that MD damaged passive avoidance induced by foot shock and hotness, and EE restored it partially. In the CA1, MD raised CRF levels and OTR levels. Parallelly, MD increased synaptic connection levels but reduced the branches' numbers of pyramidal neurons. Meanwhile, in the DG, MD increased OTR levels but lowered CRF levels, DNA levels, and spine densities. EE did not change the CA1 and DG's CRF and OTR levels. However, EE added DG's dendrites of granular cells. The additive of MD and EE raised CA1's synaptophysin and DG's postsynaptic density protein-95 and OTR levels, and meanwhile, shaped avoidance behaviors primarily similar to the control. The results suggest that experience-driven avoidance change and hippocampal neuronal plasticity are associated with local CRF and OTR levels in female mice.

Vasopressin as a Possible Link between Sleep-Disturbances and Memory Problems

Normal biological rhythms, including sleep, are very important for a healthy life and their disturbance may induce-among other issues-memory impairment, which is a key problem of many psychiatric pathologies. The major brain center of circadian regulation is the suprachiasmatic nucleus, and vasopressin (AVP), which is one of its main neurotransmitters, also plays a key role in memory formation. In this review paper, we aimed to summarize our knowledge on the vasopressinergic connection between sleep and memory with the help of the AVP-deficient Brattleboro rat strain. These animals have EEG disturbances with reduced sleep and impaired memory-boosting theta oscillation and show memory impairment in parallel. Based upon human and animal data measuring AVP levels, haplotypes, and the administration of AVP or its agonist or antagonist via different routes (subcutaneous, intraperitoneal, intracerebroventricular, or intranasal), V1a receptors (especially of hippocampal origin) were implicated in the sleep-memory interaction. All in all, the presented data confirm the possible connective role of AVP between biological rhythms and memory formation, thus, supporting the importance of AVP in several psychopathological conditions.

The central extended amygdala guides survival-relevant tradeoffs: Implications for understanding common psychiatric disorders

To thrive in challenging environments, individuals must pursue rewards while avoiding threats. Extensive studies in animals and humans have identified the central extended amygdala (EAc)-which includes the central nucleus of the amygdala (Ce) and bed nucleus of the stria terminalis (BST)-as a conserved substrate for defensive behavior. These studies suggest the EAc influences defensive responding and assembles fearful and anxious states. This has led to the proliferation of a view that the EAc is fundamentally a defensive substrate. Yet mechanistic work in animals has implicated the EAc in numerous appetitive and consummatory processes, yielding fresh insights into the microcircuitry of survival- and emotion-relevant response selection. Coupled with the EAc's centrality in a conserved network of brain regions that encode multisensory environmental and interoceptive information, these findings suggest a broader role for the EAc as an arbiter of survival- and emotion-relevant tradeoffs for action selection. Determining how the EAc optimizes these tradeoffs promises to improve our understanding of common psychiatric illnesses such as anxiety, depression, alcohol- and substance-use disorders, and anhedonia.

Oro-mucosal administration of oxytocin using medicated lollipops alters social attention, similar to intranasal and lingual routes: Implications for therapeutic use

A key functional effect of intranasal administration of the neuropeptide oxytocin is on top-down control of social attention. However, an oro-mucosal administration route may be better tolerated for chronic therapeutic use and evidence suggests that some functional effects of oxytocin can be mediated via peripheral routes. The current study investigated if oxytocin administered orally using medicated lollipops can both increase blood oxytocin concentrations and influence social attention and state anxiety. In a randomized, double-blind, clinical trial adult male participants received oral oxytocin (24IU) or placebo 30-min before completing a well-established anti-saccade paradigm which can assess treatment effects on both top-down and bottom-up attention. Oxytocin administration modulated top-down social attentional processing by increasing anti-saccade error rates on both social and non-social stimuli although it only increased response latencies for social cues. Anti-saccade errors were also positively associated with the proportionate increase in plasma oxytocin concentrations. A comparison analysis showed that oral oxytocin administration increased blood concentrations to a similar degree as given by lingual spray, although less than when given intranasally. Importantly, attentional and anxiolytic effects of oxytocin in the anti-saccade task were similar across intranasal, lingual, and oral administration routes. These findings demonstrate that oral administration of oxytocin, similar to via intranasal and lingual routes, can modulate top-down social attention and state anxiety and support its potential for therapeutic use. They also provide further evidence that functional effects of exogenously administered oxytocin can be mediated indirectly either by crossing the blood brain barrier or producing receptor mediated vagal stimulation, as opposed to via direct entry into the brain.

Ablation of the Presynaptic Protein Mover Impairs Learning Performance and Decreases Anxiety Behavior in Mice

The presynaptic protein Mover/TPRGL/SVAP30 is absent in Drosophila and C. elegans and differentially expressed in synapses in the rodent brain, suggesting that it confers specific functions to subtypes of presynaptic terminals. In order to investigate how the absence of this protein affects behavior and learning, Mover knockout mice (KO) were subjected to a series of established learning tests. To determine possible behavioral and cognitive alterations, male and female 8-week-old KO and C57Bl/6J wildtype (WT) control mice were tested in a battery of memory and anxiety tests. Testing included the cross maze, novel object recognition test (NOR), the Morris water maze (MWM), the elevated plus maze (EPM), and the open field test (OF). Mover KO mice showed impaired recognition memory in the NOR test, and decreased anxiety behavior in the OF and the EPM. Mover KO did not lead to changes in working memory in the cross maze or spatial reference memory in the MWM. However, a detailed analysis of the swimming strategies demonstrated allocentric-specific memory deficits in male KO mice. Our data indicate that Mover appears to control synaptic properties associated with specific forms of memory formation and behavior, suggesting that it has a modulatory role in synaptic transmission.

Oxytocin, Vasopressin, and Social Behavior: From Neural Circuits to Clinical Opportunities

Oxytocin and vasopressin are peptide hormones secreted from the pituitary that are well known for their peripheral endocrine effects on childbirth/nursing and blood pressure/urine concentration, respectively. However, both peptides are also released in the brain, where they modulate several aspects of social behaviors. Oxytocin promotes maternal nurturing and bonding, enhances social reward, and increases the salience of social stimuli. Vasopressin modulates social communication, social investigation, territorial behavior, and aggression, predominantly in males. Both peptides facilitate social memory and pair bonding behaviors in monogamous species. Here we review the latest research delineating the neural circuitry of the brain oxytocin and vasopressin systems and summarize recent investigations into the circuit-based mechanisms modulating social behaviors. We highlight research using modern molecular genetic technologies to map, monitor activity of, or manipulate neuropeptide circuits. Species diversity in oxytocin and vasopressin effects on social behaviors are also discussed. We conclude with a discussion of the translational implications of oxytocin and vasopressin for improving social functioning in disorders with social impairments, such as autism spectrum disorder.

OXTR DNA methylation differentiates men on the obesity spectrum with and without binge eating disorder

BACKGROUND

The neuropeptide oxytocin (OXT) plays a role in the regulation of eating behavior and metabolism. OXT functioning is altered in patients with eating and weight disorders, and a variant of the oxytocin receptor gene (OXTR) has been associated with impulsive eating behavior as it is seen in patients with binge eating disorder (BED). Gene × environment interactions could play a role in BED. One mechanism mediating this interaction is the epigenetic alteration of gene expression. We therefore investigated if DNA methylation of the OXTR differs between individuals with obesity depending on a comorbid BED. We analyzed DNA methylation of the OXTR in peripheral blood of 227 individuals on the obesity spectrum (mean age: 40.3 ± 13.1 yrs; mean BMI: 38.6 ± 7.3 kg/m²), 130 of which were diagnosed with BED.

RESULTS

There were no overall differences in OXTR methylation between participants with and those without BED (p > 0.05), while both subgroups were comparable regarding age and body mass index (BMI), but significantly differed in sex distribution (p = 0.035). We found no relationship between mean DNA methylation and BMI or self-reported eating disorder (ED) pathology. Analyzing potential sex differences revealed a significantly lower OXTR DNA methylation in male participants with BED as compared to those without BED (p = 0.017). No such difference was found in the female subsample (p > 0.05).

CONCLUSIONS

Clinically significant binge eating pathology might be associated with lower OXTR DNA methylation exclusively in males. The differential DNA methylation of OXTR in males with BED supports the view that BED represents a phenotype within the obesity spectrum that is characterized by specific vulnerability factors. A better understanding of the epigenetic underpinnings of the OXT system might contribute to the refinement of OXT administration approaches as potential interventions in eating and weight disorders.

Impact of adolescent intermittent ethanol exposure in male and female rats on social drinking and neuropeptide gene expression

BACKGROUND

Alcohol use during adolescence can alter maturational changes that occur in brain regions associated with social and emotional responding. Our previous studies have shown that adult male, but not female rats demonstrate social anxiety-like alterations and enhanced sensitivity to ethanol-induced social facilitation following adolescent intermittent ethanol exposure (AIE). These consequences of AIE may influence adult social drinking in a sex-specific manner.

METHODS

To test the effects of AIE on social drinking, male and female Sprague-Dawley rats exposed to water or ethanol (0 or 4 g/kg, intragastrically, every other day, between postnatal day [P] 25 and 45) were tested as adults (P72-83) in a social drinking paradigm (30-minute access to a 10% ethanol solution in supersac or supersac alone in groups of three same-sex littermates across two 4-day cycles separated by 4 days off). Social behavior was assessed during the last drinking session, along with assessment of oxytocin (OXT), oxytocin receptor (OXTR), vasopressin (AVP), and vasopressin receptors 1a and 1b (AVPR1a, AVPR1b) in the hypothalamus and lateral septum.

RESULTS

Males exposed to AIE consumed more ethanol than water-exposed controls during the second drinking cycle, whereas AIE did not affect supersac intake in males. AIE-exposed females consumed less ethanol and more supersac than water-exposed controls. Water-exposed females drinking ethanol showed more social investigation and significantly higher hypothalamic OXTR, AVP, and AVPR1b gene expression than their counterparts ingesting supersac and AIE females drinking ethanol. In males, hypothalamic AVPR1b gene expression was affected by drinking solution, with significantly higher expression evident in males drinking ethanol than those consuming supersac.

CONCLUSIONS

Collectively, these findings provide new evidence regarding sex-specific effects of AIE on social drinking and suggest that the hypothalamic OXT and AVP systems are implicated in the effects of ingested ethanol on social behavior in a sex- and adolescent-exposure-dependent manner.

Brain systems in cocaine abstinence-induced anxiety-like behavior in rodents: A review

Cocaine use disorder (CUD) is a significant public health issue that generates substantial personal, familial, and economic burdens. Still, there are no FDA-approved pharmacotherapies for CUD. Cocaine-dependent individuals report anxiety during withdrawal, and alleviation of anxiety and other negative affective states may be critical for maintaining drug abstinence. However, the neurobiological mechanisms underlying abstinence-related anxiety in humans or anxiety-like behavior in rodents are not fully understood. This review summarizes investigations regarding anxiety-like behavior in mice and rats undergoing cocaine abstinence, as assessed using four of the most common anxiety-related assays: the elevated plus (or its derivative, the elevated zero) maze, open field test, light-dark transition test, and defensive burying task. We first summarize available evidence that cocaine abstinence generates anxiety-like behavior that persists throughout protracted abstinence. Then, we examine investigations concerning neuropeptide, neurotransmitter, and neuromodulator systems in cocaine abstinence-induced anxiety-like behavior. Throughout, we discuss how differences in sex, rodent strain, cocaine dose and dosing strategy and abstinence duration interact to generate anxiety-like behavior.

Hypermethylation of the oxytocin receptor gene (OXTR) in obsessive-compulsive disorder: further evidence for a biomarker of disease and treatment response

Obsessive-compulsive disorder (OCD) has recently been linked to increased methylation levels in the oxytocin receptor (OXTR) gene, and OXTR hypermethylation has predicted a worse treatment response to cognitive-behavioural therapy (CBT). Furthermore, OCD is associated with childhood trauma and stressful life events, which have both been shown to affect OXTR methylation. Here, we aimed to replicate findings of increased OXTR methylation as a predictor of disease and worse treatment response in an independent sample that received treatment within the public health care system. In addition, we aimed to extend previous findings by examining associations between OXTR hypermethylation, environmental stressors, OCD diagnosis, and treatment response. Methylation levels at two CpGs within OXTR exon III were compared between n = 181 OCD patients and n = 199 healthy controls using linear regression analysis. In a subsample of OCD patients (n = 98) with documented treatment data, we examined associations between methylation and treatment response to CBT. Childhood adversity and stressful life events were assessed using Childhood Trauma Questionnaire and Life Experience Survey, respectively. OCD patients exhibited significant hypermethylation at CpG site cg04523291 compared to controls, and increased methylation was associated with impaired treatment response. Moreover, hypermethylation at cg04523291 was associated with stressful life events in OCD patients, and with childhood adversity in controls. Yet, there were no significant mediation effects. In conclusion, we replicated the association between OXTR hypermethylation and OCD in the largest sample, so far. Furthermore, our findings support the role of OXTR methylation as a promising biomarker for treatment response in OCD.

Behavioral alterations induced by intermittent ethanol intake and noise exposure in adolescent rats

Alcohol intake and exposure to noise are common activities of human adolescents performed in entertainment contexts worldwide that can induce behavioral disturbances. Therefore, the aim of the present work was to investigate in an experimental model of adolescent animals whether noise exposure and intermittent ethanol intake, when present individually or sequentially, might be able to modify different behaviors. Adolescent Wistar rats of both sexes were subjected to voluntary intermittent ethanol intake for 1 week followed by exposure to noise for 2 h and tested in a battery of behavioral tasks. Data show that males exposed to noise experienced a deficit in associative memory (AM), increase in anxiety-like behaviors (ALB) and altered reaction to novelty (RN) when compared with sham animals, whereas females also showed an increase in risk assessment behaviors (RAB) and a decrease in exploratory activity (EA). In contrast, ethanol intake induced an increase in RAB and RN in males and females, whereas females also showed a deficit in AM and EA as well as an increase in ALB. When ethanol was ingested before noise exposure, most parameters were counteracted both in male and females, but differed among sexes. In consequence, it could be hypothesized that an environmental acute stressor like noise might trigger a behavioral counteracting induced by a previous repeated exposure to a chemical agent such as ethanol, leading to a compensation of a non-adaptive behavior and reaching a better adjustment to the environment.

The Sexual Dimorphic Synapse: From Spine Density to Molecular Composition

A synaptic sexual dimorphism is relevant in the context of multiple neurodevelopmental, neurodegenerative, and neuropsychiatric disorders. Many of these disorders show a different prevalence and progression in woman and man. A similar variance is also present in corresponding animal models. To understand and characterize this dimorphism in pathologies it is important to first understand sex differences in unaffected individuals. Therefore, sexual differences have been studied since 1788, first focusing on brain weight, size, and volume. But as these measures are not directly related to brain function, the investigation of sexual dimorphism also expanded to other organizational levels of the brain. This review is focused on sexual dimorphism at the synaptic level, as these specialized structures are the smallest functional units of the brain, determining cell communication, connectivity, and plasticity. Multiple differences between males and females can be found on the levels of spine density, synaptic morphology, and molecular synapse composition. These differences support the importance of sex-disaggregated data. The specificity of changes to a particular brain region or circuit might support the idea of a mosaic brain, in which each tile individually lies on a continuum from masculinization to feminization. Moreover, synapses can be seen as the smallest tiles of the mosaic determining the classification of larger areas.

Oxytocin and love: Myths, metaphors and mysteries

Oxytocin is a peptide molecule with a multitude of physiological and behavioral functions. Based on its association with reproduction - including social bonding, sexual behavior, birth and maternal behavior - oxytocin also has been called "the love hormone." This essay specifically examines association and parallels between oxytocin and love. However, many myths and gaps in knowledge remain concerning both. A few of these are described here and we hypothesize that the potential benefits of both love and oxytocin may be better understood in light of interactions with more ancient systems, including specifically vasopressin and the immune system. Oxytocin is anti-inflammatory and is associated with recently evolved, social solutions to a variety of challenges necessary for mammalian survival and reproduction. The shared functions of oxytocin and love have profound implications for health and longevity, including the prevention and treatment of excess inflammation and related disorders, especially those occurring in early life and during periods of chronic threat or disease.

Sex-dependent features of social behavior differ between distinct laboratory mouse strains and their mixed offspring

The survival of individuals of gregarious species depends on their social interactions. In humans, atypical social behavior is a hallmark of several psychopathological conditions, many of which have sex-specific manifestations. Various laboratory mouse strains are used to reveal the mechanisms mediating typical and atypical social behavior in mammals. Here, we used three social discrimination tests to characterize social behavior in males and females of three widely used laboratory mouse strains (C57BL/6J, BALB/c, and ICR). We found marked sex- and strain-specific differences in the behavior exhibited by subjects, in a test-dependent manner. Interestingly, some characteristics were strain-dependent, while others were sex-dependent. We then crossbred C57BL/6J and BALB/c mice and found that offspring of such crossbreeding exhibit social behavior which differs from both parental strains and depends on the specific combination of parental strains. Thus, social behavior of laboratory mice is sex- and strain-specific and depends on both genetic and environmental factors.

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Social investigation behavior of laboratory mice is highly strain- and sex-specific

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Some behavioral aspects are either strain- or sex-specific, but not both

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Mixed offspring of distinct strains behave differently from both parental strains

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The behavior of mixed offspring depends on the specific combination of parents

Rescue of Vasopressin Synthesis in Magnocellular Neurons of the Supraoptic Nucleus Normalises Acute Stress-Induced Adrenocorticotropin Secretion and Unmasks an Effect on Social Behaviour in Male Vasopressin-Deficient Brattleboro Rats

The relevance of vasopressin (AVP) of magnocellular origin to the regulation of the endocrine stress axis and related behaviour is still under discussion. We aimed to obtain deeper insight into this process. To rescue magnocellular AVP synthesis, a vasopressin-containing adeno-associated virus vector (AVP-AAV) was injected into the supraoptic nucleus (SON) of AVP-deficient Brattleboro rats (di/di). We compared +/+, di/di, and AVP-AAV treated di/di male rats. The AVP-AAV treatment rescued the AVP synthesis in the SON both morphologically and functionally. It also rescued the peak of adrenocorticotropin release triggered by immune and metabolic challenges without affecting corticosterone levels. The elevated corticotropin-releasing hormone receptor 1 mRNA levels in the anterior pituitary of di/di-rats were diminished by the AVP-AAV-treatment. The altered c-Fos synthesis in di/di-rats in response to a metabolic stressor was normalised by AVP-AAV in both the SON and medial amygdala (MeA), but not in the central and basolateral amygdala or lateral hypothalamus. In vitro electrophysiological recordings showed an AVP-induced inhibition of MeA neurons that was prevented by picrotoxin administration, supporting the possible regulatory role of AVP originating in the SON. A memory deficit in the novel object recognition test seen in di/di animals remained unaffected by AVP-AAV treatment. Interestingly, although di/di rats show intact social investigation and aggression, the SON AVP-AAV treatment resulted in an alteration of these social behaviours. AVP released from the magnocellular SON neurons may stimulate adrenocorticotropin secretion in response to defined stressors and might participate in the fine-tuning of social behaviour with a possible contribution from the MeA.