Sex differences in social investigation: effects of androgen receptors, hormones and test partner

Sex differences in socioemotional behavior and changes in ventral hippocampal transcription across aging in C57Bl/6J mice

Socioemotional health is positively correlated with improved cognitive and physical aging. Despite known sex differences in socioemotional behaviors and the trajectory of aging, the interactive effects between sex and aging on socioemotional outcomes are poorly understood. We performed the most comprehensive assessment of sex differences in socioemotional behaviors in C57Bl/6J mice across aging to date. Compared to males, females exhibited decreased anxiety-like behavior and social preference but increased social recognition. With age, anxiety-like behavior, cued threat memory generalization, and social preference increased in both sexes. To investigate potential neural mechanisms underlying these behavioral changes, we analyzed transcriptional neuropathology markers in the ventral hippocampus and found age-related changes in genes related to activated microglia, angiogenesis, and cytokines. Sex differences emerged in the timing, direction, and magnitude of these changes, independent of reproductive senescence in aged females. Interestingly, female-specific upregulation of autophagy-related genes correlated with age-related behavioral changes selectively in females. These novel findings reveal critical sex differences in trajectories of ventral hippocampal aging that may contribute to sex- and age-related differences in socioemotional outcomes.

ZIP9 mediates the effects of DHT on learning, memory and hippocampal synaptic plasticity of male Tfm and APP/PS1 mice

Androgens are closely associated with functions of hippocampal learning, memory, and synaptic plasticity. The zinc transporter ZIP9 (SLC39A9) regulates androgen effects as a binding site distinct from the androgen receptor (AR). However, it is still unclear whether androgens regulate their functions in hippocampus of mice through ZIP9. Compared with wild-type (WT) male mice, we found that AR-deficient male testicular feminization mutation (Tfm) mice with low androgen levels had learning and memory impairment, decreased expression of hippocampal synaptic proteins PSD95, drebrin, SYP, and dendritic spine density. Dihydrotestosterone (DHT) supplementation significantly improved these conditions in Tfm male mice, although the beneficial effects disappeared after hippocampal ZIP9 knockdown. To explore the underlying mechanism, we first detected the phosphorylation of ERK1/2 and eIF4E in the hippocampus and found that it was lower in Tfm male mice than in WT male mice, it upregulated with DHT supplementation, and it downregulated after hippocampal ZIP9 knockdown. Next, we found that the expression of PSD95, p-ERK1/2, and p-eIF4E increased in DHT-treated mouse hippocampal neuron HT22 cells, and ZIP9 knockdown or overexpression inhibited or further enhanced these effects. Using the ERK1/2 specific inhibitor SCH772984 and eIF4E specific inhibitor eFT508, we found that DHT activated ERK1/2 through ZIP9, resulting in eIF4E phosphorylation, thus promoting PSD95 protein expression in HT22 cells. Finally, we found that ZIP9 mediated the effects of DHT on the expression of synaptic proteins PSD95, drebrin, SYP, and dendritic spine density in the hippocampus of APP/PS1 mice through the ERK1/2-eIF4E pathway and affected learning and memory. This study demonstrated that androgen affected learning and memory in mice through ZIP9, providing new experimental evidence for improvement in learning and memory in Alzheimer's disease with androgen supplementation.

Development of social recognition ability in female rats: Effect of pubertal ovarian hormones

The ability to recognize previously encountered conspecifics is crucial for social interaction. This social recognition ability is well characterized in adult rodents of both sexes but remains largely unexplored in juveniles. Using the social discrimination test of social recognition with short intervals (30 min and 1 h), we first found that juvenile female rats do not display a difference in investigation directed toward a novel vs. familiar stimulus rat. Using the social discrimination test with a 30-minute interval, we then showed that social recognition is established by the time of adolescence in female rats. Based on these findings, we hypothesized that social recognition is dependent on the initiation of ovarian hormone release during puberty. To test this, we ovariectomized females prior to puberty and found that prepubertal ovariectomy prevented the development of social recognition ability in adulthood. Administration of estradiol benzoate, 48 h prior to testing, to juvenile females or prepubertally ovariectomized adult females did not restore social recognition, suggesting that ovarian hormones organize the neural circuitry regulating this behavior during adolescence. These findings provide the first evidence of an effect of pubertal development on social recognition ability in female rats and highlight the importance of considering sex and age when interpreting results from behavioral paradigms initially designed for use in adult 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.

Neuroendocrine underpinning of social recognition in males and females

Social recognition is an essential skill for the expression of appropriate behaviors towards conspecifics in most social species. Several studies point to oxytocin (OT) and arginine vasopressin (AVP) as key mediators of social recognition in males and females. However, sex differences in social cognitive behaviors highlight an important interplay between OT, AVP and the sex steroids. Estrogens facilitate social recognition by regulating OT action in the hypothalamus and that of OT receptor in the medial amygdala. The role of OT in these brain regions appears to be essential for social recognition in both males and females. Conversely, social recognition in male rats and mice is more dependent on AVP release in the lateral septum than in females. The AVP system comprises a series of highly sexually dimorphic brain nuclei, including the bed nucleus of the stria terminalis, the amygdala and the lateral septum. Various studies suggest that testosterone and its metabolites, including estradiol, influence social recognition in males by modulating the activity of the AVP at V1a receptor. Intriguingly, both estrogens and androgens can affect social recognition very rapidly, through non-genomic mechanisms. In addition, the androgen metabolites, namely 3α-diol and 3β-diol, may also have an impact on social behaviors either by interacting with the estrogen receptors or through other mechanisms. Overall, the regulation of OT and AVP by sex steroids fine tunes social recognition and the behaviors that depend upon it (e.g., social bond, hierarchical organization, aggression) in a sex-dependent manner. Elucidating the sex-dependent interaction between sex steroids and neuroendocrine systems is essential for understanding sex differences in the normal and abnormal expression of social behaviors.

Four Core Genotypes and XY* mouse models: Update on impact on SABV research

The impact of two mouse models is reviewed, the Four Core Genotypes and XY* models. The models are useful for determining if the causes of sex differences in phenotypes are either hormonal or sex chromosomal, or both. Used together, the models also can distinguish between the effects of X or Y chromosome genes that contribute to sex differences in phenotypes. To date, the models have been used to uncover sex chromosome contributions to sex differences in a wide variety of phenotypes, including brain and behavior, autoimmunity and immunity, cardiovascular disease, metabolism, and Alzheimer's Disease. In some cases, use of the models has been a strategy leading to discovery of specific X or Y genes that protect from or exacerbate disease. Sex chromosome and hormonal factors interact, in some cases to reduce the effects of each other. Future progress will come from more extensive application of these models, and development of similar models in other species.

A Single Test to Study Social Behavior and Repetitive Self-grooming in Mice

The ability to recognize and interact with members of the same species is essential for social communication. Investigating the neural substrates of social interest and recognition may offer insights into the behavioral differences present in disorders affecting social behavior. Assays used to study social interest in rodents include the 3-chamber test, a partition test, and a social interaction test. Here, we present a single protocol that can be used to quantify the level of social interest displayed by mice, the ability to distinguish between different individual mice (social recognition), and the level of repetitive self-grooming displayed. In the first part of the protocol, a social habituation/dishabituation test, the time spent by a test mouse sniffing a stimulus mouse is quantified over 9 trials. In the first 8 interactions, the same stimulus mouse is used repeatedly; on the ninth trial, a novel stimulus mouse is presented. Intact social recognition is indicated by a progressive decrease in the investigation time over trials 1-8, and an increase in trial 9. The interval between each social trial is used to quantify self-grooming, a stereotyped repetitive behavior in mice. We also present a method for randomized, blinded analysis of these behaviors to increase rigor and reproducibility of results. Therefore, this single behavioral test enables ready assessment of phenotypes of both social and repetitive behaviors in an integrated manner in the same animals. This feature can be advantageous in understanding interactions between these behaviors and phenotypes in mouse models with genetic variants associated with autism and other neurodevelopmental or neuropsychiatric disorders, which are often characterized by these behavioral differences.

Transgenerational Bisphenol A Causes Deficits in Social Recognition and Alters Postsynaptic Density Genes in Mice

Bisphenol A (BPA) is a ubiquitous endocrine-disrupting chemical. Developmental exposure produces changes in behavior and gene expression in the brain. Here, we examined social recognition behaviors in mice from the third familial generation (F3) after exposure to gestational BPA. Second-generation mice were bred in one of four mating combinations to reveal whether characteristics in F3 were acquired via maternal or paternal exposures. After repeated habituation to the same mouse, offspring of dams from the BPA lineage failed to display increased investigation of a novel mouse. Genes involved in excitatory postsynaptic densities (PSDs) were examined in F3 brains using quantitative PCR. Differential expression of genes important for function and stability of PSDs were assessed at three developmental ages. Several related PSD genes-SH3 and multiple ankyrin repeat domains 1 (Shank1), Homer scaffolding protein 1c (Homer1c), DLG associated protein 1 (Gkap), and discs large MAGUK scaffold protein 4 (PSD95)-were differentially expressed in control- vs BPA-lineage brains. Using a second strain of F3 inbred mice exposed to BPA, we noted the same differences in Shank1 and PSD95 expression in C57BL/6J mice. In sum, transgenerational BPA exposure disrupted social interactions in mice and dysregulated normal expression of PSD genes during neural development. The fact that the same genetic effects were found in two different mouse strains and in several brain regions increased potential for translation. The genetic and functional relationship between PSD and abnormal neurobehavioral disorders is well established, and our data suggest that BPA may contribute in a transgenerational manner to neurodevelopmental diseases.

Individual differences in the biological basis of androphilia in mice and men

For nearly 60 years since the seminal paper from W.C Young and colleagues (Phoenix et al., 1959), the principles of sexual differentiation of the brain and behavior have maintained that female-typical sexual behaviors (e.g., lordosis) and sexual preferences (e.g., attraction to males) are the result of low androgen levels during development, whereas higher androgen levels promote male-typical sexual behaviors (e.g., mounting and thrusting) and preferences (e.g., attraction to females). However, recent reports suggest that the relationship between androgens and male-typical behaviors is not always linear - when androgen signaling is increased in male rodents, via exogenous androgen exposure or androgen receptor overexpression, males continue to exhibit male-typical sexual behaviors, but their sexual preferences are altered such that their interest in same-sex partners is increased. Analogous to this rodent literature, recent findings indicate that high level androgen exposure may contribute to the sexual orientation of a subset of gay men who prefer insertive anal sex and report more male-typical gender traits, whereas gay men who prefer receptive anal sex, and who on average report more gender nonconformity, present with biomarkers suggestive of low androgen exposure. Together, the evidence indicates that for both mice and men there is an inverted-U curvilinear relationship between androgens and sexual preferences, such that low and high androgen exposure increases androphilic sexual attraction, whereas relative mid-range androgen exposure leads to gynephilic attraction. Future directions for studying how individual differences in biological development mediate sexual behavior and sexual preferences in both mice and humans are discussed.

Object, spatial and social recognition testing in a single test paradigm

Animals have the ability to process information about an object or a conspecific's physical features and location, and alter its behavior when such information is updated. In the laboratory, the object, spatial and social recognition are often studied in separate tasks, making them unsuitable to study the potential dissociations and interactions among various types of recognition memories. The present study introduced a single paradigm to detect the object and spatial recognition, and social recognition of a familiar and novel conspecific. Specifically, male and female Sprague-Dawley adult (>75 days old) or preadolescent (25-28 days old) rats were tested with two objects and one social partner in an open-field arena for four 10-min sessions with a 20-min inter-session interval. After the first sample session, a new object replaced one of the sampled objects in the second session, and the location of one of the old objects was changed in the third session. Finally, a new social partner was introduced in the fourth session and replaced the familiar one. Exploration time with each stimulus was recorded and measures for the three recognitions were calculated based on the discrimination ratio. Overall results show that adult and preadolescent male and female rats spent more time exploring the social partner than the objects, showing a clear preference for social stimulus over nonsocial one. They also did not differ in their abilities to discriminate a new object, a new location and a new social partner from a familiar one, and to recognize a familiar conspecific. Acute administration of MK-801 (a NMDA receptor antagonist, 0.025 and 0.10 mg/kg, i.p.) after the sample session dose-dependently reduced the total time spent on exploring the social partner and objects in the adult rats, and had a significantly larger effect in the females than in the males. MK-801 also dose-dependently increased motor activity. However, it did not alter the object, spatial and social recognitions. These findings indicate that the new triple recognition paradigm is capable of recording the object, spatial location and social recognition together and revealing potential sex and age differences. This paradigm is also useful for the study of object and social exploration concurrently and can be used to evaluate cognition-altering drugs in various stages of recognition memories.

Genetic loss of diazepam binding inhibitor in mice impairs social interest

Neuropsychiatric disorders in which reduced social interest is a common symptom, such as autism, depression, and anxiety, are frequently associated with genetic mutations affecting γ-aminobutyric acid (GABA)ergic transmission. Benzodiazepine treatment, acting via GABA type-A receptors, improves social interaction in male mouse models with autism-like features. The protein diazepam binding inhibitor (DBI) can act as an endogenous benzodiazepine, but a role for DBI in social behavior has not been described. Here, we investigated the role of DBI in the social interest and recognition behavior of mice. The responses of DBI wild-type and knockout male and female mice to ovariectomized female wild-type mice (a neutral social stimulus) were evaluated in a habituation/dishabituation task. Both male and female knockout mice exhibited reduced social interest, and DBI knockout mice lacked the sex difference in social interest levels observed in wild-type mice, in which males showed higher social interest levels than females. The ability to discriminate between familiar and novel stimulus mice (social recognition) was not impaired in DBI-deficient mice of either sex. DBI knockouts could learn a rotarod motor task, and could discriminate between social and nonsocial odors. Both sexes of DBI knockout mice showed increased repetitive grooming behavior, but not in a manner that would account for the decrease in social investigation time. Genetic loss of DBI did not alter seminal vesicle weight, indicating that the social interest phenotype of males lacking DBI is not due to reduced circulating testosterone. Together, these studies show a novel role of DBI in driving social interest and motivation.

Neural Androgen Receptors Modulate Gene Expression and Social Recognition But Not Social Investigation

The role of sex and androgen receptors (ARs) for social preference and social memory is rather unknown. In this study of mice we compared males, females and males lacking ARs specifically in the nervous system, AR^NesDel, with respect to social preference, assessed with the three-chambered apparatus test, and social recognition, assessed with the social discrimination procedure. In the social discrimination test we also evaluated the tentative importance of the sex of the stimulus animal. Novel object recognition and olfaction were investigated to complement the results from the social tests. Gene expression analysis was performed to reveal molecules involved in the effects of sex and androgens on social behaviors. All three test groups showed social preference in the three-chambered apparatus test. In both social tests an AR-independent sexual dimorphism was seen in the persistence of social investigation of female conspecifics, whereas the social interest toward male stimuli mice was similar in all groups. Male and female controls recognized conspecifics independent of their sex, whereas AR^NesDel males recognized female but not male stimuli mice. Moreover, the non-social behaviors were not affected by AR deficiency. The gene expression analyses of hypothalamus and amygdala indicated that Oxtr, Cd38, Esr1, Cyp19a1, Ucn3, Crh, and Gtf2i were differentially expressed between the three groups. In conclusion, our results suggest that ARs are required for recognition of male but not female conspecifics, while being dispensable for social investigation toward both sexes. In addition, the AR seems to regulate genes related to oxytocin, estrogen and William’s syndrome.

Altered social cognition in male BDNF heterozygous mice and following chronic methamphetamine exposure

Growing clinical evidence suggests that persistent psychosis which occurs in methamphetamine users is closely related to schizophrenia. However, preclinical studies in animal models have focussed on psychosis-related behaviours following methamphetamine, and less work has been done to assess endophenotypes relevant to other deficits observed in schizophrenia. Altered social behaviour is a feature of both the negative symptoms and cognitive deficits in schizophrenia, and significantly impacts patient functioning. We recently found that brain-derived neurotrophic factor (BDNF) heterozygous mice show disrupted sensitization to methamphetamine, supporting other work suggesting an important role of this neurotrophin in the pathophysiology of psychosis and the neuronal response to stimulant drugs. In the current study, we assessed social and cognitive behaviours in methamphetamine-treated BDNF heterozygous mice and wildtype littermate controls. Following chronic methamphetamine exposure male wildtype mice showed a 50% reduction in social novelty preference. Vehicle-treated male BDNF heterozygous mice showed a similar impairment in social novelty preference, with a trend for no further disruption by methamphetamine exposure. Female mice were unaffected in this task, and no groups showed any changes in sociability or short-term spatial memory. These findings suggest that chronic methamphetamine alters behaviour relevant to disruption of social cognition in schizophrenia, supporting other studies which demonstrate a close resemblance between persistent methamphetamine psychosis and schizophrenia. Together these findings suggest that dynamic regulation of BDNF signalling is necessary to mediate the effects of methamphetamine on behaviours relevant to schizophrenia.

Immune deficiency influences juvenile social behavior and maternal behavior

Mice with severe combined immunodeficiency (SCID) lack functional T and B lymphocytes, and have impaired cognitive abilities. We assessed social behaviors in male SCID and C57BL/6 (B6) juvenile mice. In a social preference task, SCID mice spent more time than B6 mice investigating a novel adult male mouse. In a social recognition task, SCID mice habituated to a novel ovariectomized mouse, but failed to show dishabituation when presented with an unfamiliar individual. We hypothesized that partial immune restoration could normalize behaviors. SCID pups (postnatal Day 7) received either saline or splenocytes from normal donors. Splenocyte-replaced SCID mice spent less time interacting with a novel mouse than saline-injected SCID or B6 control mice. Again, control SCID mice failed to dishabituate to a novel mouse, but splenocyte-replaced SCID mice showed dishabituation. In both of these studies, B6 and SCID pairs were used to produce offspring that remained with their dams until weaning. There are no studies of maternal behavior in SCID dams; therefore to investigate the potential role for this factor, we quantified maternal behavior in SCID and B6 dams; several significant differences were found. To control for differences in maternal care, we mated heterozygous SCIDs to produce offspring. These homozygous SCID and wild-type offspring reared by dams of the same genotypes displayed similar responses to a novel mouse; however, in the social recognition task, SCID males did not display dishabituation to a novel mouse. Taken together, our data indicate that Gene × Environment interactions influence social interactions in immune deficient mice.

Effects of sex and gonadectomy on social investigation and social recognition in mice

Background

An individual’s ability to recognise and pay attention to others is crucial in order to behave appropriately in various social situations. Studies in humans have shown a sex bias in sociability as well as social memory, indicating that females have better face memory and gaze more at the eyes of others, but information about the factors that underpin these differences is sparse. Our aim was therefore to investigate if sociability and social recognition differ between female and male mice, and if so, to what extent gonadal hormones may be involved. Intact and gonadectomised male and female mice were assessed for sociability and social recognition using the three-chambered sociability paradigm, as well as the social discrimination test. Furthermore, we conducted a novel object recognition test, a locomotor activity test and an odour habituation/dishabituation test.

Results

The present study showed that the ability to recognise other individuals is intact in males with and without gonads, as well as in intact females, whereas it is hampered in gonadectomised females. Additionally, intact male mice displayed more persistent investigatory behaviour compared to the other groups, although the intact females showed elevated basal locomotor activity. In addition, all groups had intact object memory and habituated to odours.

Conclusions

Our results suggest that intact male mice investigate conspecifics more than females do, and these differences seem to depend upon circulating hormones released from the testis. As these results seem to contrast what is known from human studies, they should be taken into consideration when using the three-chambered apparatus, and similar paradigms as animal models of social deficits in e.g. autism. Other behavioural tests, and animal models, may be more suitable for translational studies between patients and experimental animals.

Social Novelty Investigation in the Juvenile Rat: Modulation by the μ-Opioid System

The drive to approach and explore novel conspecifics is inherent to social animals and may promote optimal social functioning. Juvenile animals seek out interactions with novel peers more frequently and find these interactions to be more rewarding than their adult counterparts. In the present study, we aimed to establish a behavioural paradigm to measure social novelty-seeking in juvenile rats and to determine the involvement of the opioid, dopamine, oxytocin and vasopressin systems in this behaviour. To this end, we developed the social novelty preference test to assess the preference of a juvenile rat to investigate a novel over a familiar (cage mate) conspecific. We show that across the juvenile period both male and female rats spend more time investigating a novel conspecific than a cage mate, independent of subject sex or repeated exposure to the test. We hypothesised that brain systems subserving social information processing and social motivation/reward (i.e. the opioid, dopamine, oxytocin, vasopressin systems) might support social novelty preference. To test this, receptor antagonists of each of these systems were administered i.c.v. prior to exposure to the social novelty preference test and, subsequently, to the social preference test, to examine the specificity of these effects. We find that μ-opioid receptor antagonism reduces novel social investigation in both the social novelty preference and social preference tests while leaving the investigation of a cage mate (social novelty preference test) or an object (social preference test) unaffected. In contrast, central blockade of dopamine D2 receptors (with eticlopride), oxytocin receptors (with des-Gly-NH2,d(CH2)5[Tyr(Me)2,Thr4]OVT) or vasopressin V1a receptors [with (CH2)5Tyr(Me2)AVP] failed to alter social novelty preference or social preference. Overall, we have established a new behavioural test to study social novelty-seeking behaviour in the juvenile rat and show that the μ-opioid system facilitates this behaviour, possibly by reducing risk avoidance and enhancing the hedonic and/or motivational value of social novelty.

Number of X-chromosome genes influences social behavior and vasopressin gene expression in mice

Sex differences in behavior are widespread and often caused by hormonal differences between the sexes. In addition to hormones, the composition and numbers of the sex chromosomes also affect a variety of sex differences. In humans, X-chromosome genes are implicated in neurobehavioral disorders (i.e. fragile-X, autism). To investigate the role of X-chromosome genes in social behavior, we used a mouse model that has atypical sex chromosome configurations resembling Turner (45, XO) and Klinefelter syndromes (47, XXY). We examined a number of behaviors in juvenile mice. Mice with only one copy of most X-chromosome genes, regardless of gonadal sex, were less social in dyadic interaction and social preference tasks. In the elevated plus maze, mice with one X-chromosome spent less time in the distal ends of the open arms as compared to mice with two copies of X-chromosome genes. Using qRTPCR, we noted that amygdala from female mice with one X-chromosome had higher expression levels of vasopressin (Avp) as compared to mice in the other groups. Finally, in plasma from girls with Turner syndrome we detected reduced vasopressin (AVP) concentrations as compared to control patients. These novel findings link sex chromosome genes with social behavior via concentrations of AVP in brain, adding to our understanding of sex differences in neurobehavioral disorders.

Relationships among sex, season and testosterone in the expression of androgen receptor mRNA and protein in the green anole forebrain

Sexual behavior in male green anole lizards is regulated by a seasonal increase in testosterone (T). However, T is much more effective at activating behavioral, morphological and biochemical changes related to reproduction in the breeding season (BS; spring) compared to nonbreeding season (NBS; fall). An increase in androgen receptor (AR) during the BS is one potential mechanism for this differential responsiveness. AR expression has not been investigated in specific brain regions across seasons in anoles. The present studies were designed to determine relative AR expression in areas important for male (preoptic area, ventromedial amygdala) and female (ventromedial hypothalamus) sexual behavior, as well as whether T upregulates AR in the anole brain. In situ hybridization and Western blot analyses were performed in unmanipulated animals across sex and season, as well as in gonadectomized animals with and without T treatment. Among hormone-manipulated animals, more cells expressing AR mRNA were detected in females than males in the amygdala. T treatment increased the volume of the ventromedial hypothalamus of gonadectomized animals in the BS, but not the NBS. AR protein in dissections of the hypothalamus and preoptic area was increased in males compared to females specifically in the BS. Additionally, among females, it was increased in the NBS compared to the BS. Collectively, these results indicate that differences in central AR expression probably do not facilitate a seasonal responsiveness to T. However, they are consistent with a role for AR in regulating some differences between sexes in the display of reproductive behaviors.

Early life seizures in female rats lead to anxiety-related behavior and abnormal social behavior characterized by reduced motivation to novelty and deficit in social discrimination

Previously, we demonstrated that male Wistar rats submitted to neonatal status epilepticus showed abnormal social behavior characterized by deficit in social discrimination and enhanced emotionality. Taking into account that early insult can produce different biological manifestations in a gender-dependent manner, we aimed to investigate the social behavior and anxiety-like behavior in female Wistar rats following early life seizures. Neonate female Wistar rats at 9 days postnatal were subject to pilocarpine-induced status epilepticus and the control received saline. Behavioral tests started from 60 days postnatal and were carried out only during the diestrus phase of the reproductive cycle. In sociability test experimental animals exhibited reduced motivation for social encounter and deficit in social discrimination. In open field and the elevated plus maze, experimental animals showed enhanced emotionality with no changes in basal locomotor activity. The results showed that female rats submitted to neonatal status epipepticus showed impaired social behavior, characterized by reduced motivation to novelty and deficit in social discrimination in addition to enhanced emotionality.

Ethanol induces conditioned social preference in male mice

BACKGROUND

Affiliative social interactions promote alcohol consumption, and alcohol also promotes affiliative behavior. Furthermore, for most species, moderate doses of ethanol (EtOH) and social affiliation are each rewarding. However, animal studies of drug and EtOH reward typically test individuals in isolation. To address social dimensions of EtOH reward, this study tested EtOH-induced conditioned social preference in male C57BL/6 mice with (ORCHX+T) and without (ORCHX) testosterone.

METHODS

ORCHX+T males received EtOH (0, 1, 2, or 3 g/kg) intraperitoneally and were paired 4× for 30 minutes each with 1 of 2 stimulus males: with the CS- stimulus male after saline injection and with the CS+ male following EtOH. After pairing, time spent with CS+ and CS- males was measured in a 10-minute test.

RESULTS

ORCHX+T test males showed conditioned preference for the CS+ male in response to 3 g/kg EtOH (change in preference: +71.3 ± 30.0 s/10 min, p < 0.05), but not for 0, 1, or 2 g/kg. By contrast, ORCHX males did not demonstrate conditioned preference for 3 g/kg EtOH (+16.0 ± 24.3 s/10 min, p > 0.05). In separate groups of mice, stimulus males (IS+) received EtOH during pairing to determine whether test mice prefer another intoxicated mouse. Both ORCHX+T and ORCHX test mice showed an increase in preference score for the IS+ mouse (ORCHX+T: +68.1 ± 24.0 seconds; ORCHX: +58.9 ± 19.6 seconds, p < 0.05).

CONCLUSIONS

These data demonstrate that EtOH promotes social preference in male mice, as it does in females. Testosterone enhances this effect.

Transgenerational effects of prenatal bisphenol A on social recognition

Bisphenol A (BPA) is a man-made endocrine disrupting compound used to manufacture polycarbonate plastics. It is found in plastic bottles, canned food linings, thermal receipts and other commonly used items. Over 93% of people have detectable BPA levels in their urine. Epidemiological studies report correlations between BPA levels during pregnancy and activity, anxiety, and depression in children. We fed female mice control or BPA-containing diets that produced plasma BPA concentrations similar to concentrations in humans. Females were mated and at birth, pups were fostered to control dams to limit BPA exposure to gestation in the first generation. Sibling pairs were bred to the third generation with no further BPA exposure. First (F1) and third (F3) generation juveniles were tested for social recognition and in the open field. Adult F3 mice were tested for olfactory discrimination. In both generations, BPA exposed juvenile mice displayed higher levels of investigation than controls in a social recognition task. In F3 BPA exposed mice, dishabituation to a novel female was impaired. In the open field, no differences were noted in F1 mice, while in F3, BPA lineage mice were more active than controls. No impairments were detected in F3 mice, all were able to discriminate different male urine pools and urine from water. No sex differences were found in any task. These results demonstrate that BPA exposure during gestation has long lasting, transgenerational effects on social recognition and activity in mice. These findings show that BPA exposure has transgenerational actions on behavior and have implications for human neurodevelopmental behavioral disorders.

Sex differences in oxytocin receptor binding in forebrain regions: correlations with social interest in brain region- and sex- specific ways

Social interest reflects the motivation to approach a conspecific for the assessment of social cues and is measured in rats by the amount of time spent investigating conspecifics. Virgin female rats show lower social interest towards unfamiliar juvenile conspecifics than virgin male rats. We hypothesized that the neuropeptide oxytocin (OT) may modulate sex differences in social interest because of the involvement of OT in pro-social behaviors. We determined whether there are sex differences in OT system parameters in the brain and whether these parameters would correlate with social interest. We also determined whether estrus phase or maternal experience would alter low social interest and whether this would correlate with changes in OT system parameters. Our results show that regardless of estrus phase, females have significantly lower OT receptor (OTR) binding densities than males in the majority of forebrain regions analyzed, including the nucleus accumbens, caudate putamen, lateral septum, bed nucleus of the stria terminalis, medial amygdala, and ventromedial hypothalamus. Interestingly, male social interest correlated positively with OTR binding densities in the medial amygdala, while female social interest correlated negatively with OTR binding densities in the central amygdala. Proestrus/estrus females showed similar social interest to non-estrus females despite increased OTR binding densities in several forebrain areas. Maternal experience had no immediate or long-lasting effects on social interest or OT brain parameters except for higher OTR binding in the medial amygdala in primiparous females. Together, these findings demonstrate that there are robust sex differences in OTR binding densities in multiple forebrain regions of rats and that OTR binding densities correlate with social interest in brain region- and sex-specific ways.