Genetic influences on aggressive behaviors and arousability in animals

Sex Differences in Social Cognition

In this review we explore the sex differences underlying various types of social cognition. Particular focus will be placed on the behaviors of social recognition, social learning, and aggression. Known similarities and differences between sexes in the expressions of these behaviors and the known brain regions where these behaviors are mediated are discussed. The role that the sex hormones (estrogens and androgens) have as well as possible interactions with other neurochemicals, such as oxytocin, vasopressin, and serotonin is reviewed as well. Finally, implications about these findings on the mediation of social cognition are mediated and the sex differences related to humans are considered.

Functions of habenula in reproduction and socio-reproductive behaviours

Habenula is an evolutionarily conserved structure in the brain of vertebrates. Recent reports have drawn attention to the habenula as a processing centre for emotional decision-making and its role in psychiatric disorders. Emotional decision-making process is also known to be closely associated with reproductive conditions. The habenula receives innervations from reproductive centres within the brain and signals from key reproductive neuroendocrine regulators such as gonadal sex steroids, gonadotropin-releasing hormone (GnRH), and kisspeptin. In this review, based on morphological, biochemical, physiological, and pharmacological evidence we discuss an emerging role of the habenula in reproduction. Further, we discuss the modulatory role of reproductive endocrine factors in the habenula and their association with socio-reproductive behaviours such as mating, anxiety and aggression.

Expression of ESR1 and ESR2 oestrogen receptor encoding gene and personality traits - preliminary study

INTRODUCTION

The main objective of the study is to examine the hypothesis claiming a correlation between personality traits measured with the use of the Minnesota Multiphasic Personality Inventory (MMPI-2) personality questionnaire and the expression of the ERα (ESR1) and ERβ (ESR2) encoding gene in patients suffering from depression.

MATERIAL AND METHODS

The experiment was carried out on a group of 44 individuals with depression. The Polish variant of the MMPI-2 was applied with the aim of assessing personality traits. Furthermore, the authors evaluated the expression of the genes encoding the oestrogen receptors (ERα and ERβ) at the mRNA level and protein level in the studied population.

RESULTS

No significant differences in the expression of ERα and ERβ encoding genes were found and confirmed in the patients with the first episode of depression and those suffering from subsequent episodes of the disease. No differences were found between women and men, either. In women a positive relationship was found between the scale of psychopathy (p = 0.04), paranoia (p = 0.01), and mania (p = 0.03) and expression for the ERα encoding gene at the mRNA level. A negative relationship was found between the mania scale and ERβ encoding gene expression at mRNA (p = 0.03) and protein (p = 0.04) levels. In males a positive relationship between anxiety as a personality trait and expression of the ERβ receptor encoding gene at mRNA level (p = 0.03) and protein level (p = 0.03) was found.

CONCLUSIONS

Personality traits may be linked with the expression of genes encoding oestrogen receptors (ERα and ERβ) among patients with depressive disorders.

Strain differences in intermale aggression and possible factors regulating increased aggression in Japanese quail

The National Institute for Environmental Studies (NIES) of Japan established a strain of Japanese quail (Coturnix japonica) known as NIES-L by rotation breeding in a closed colony for over 35years; accordingly, the strain has highly inbred-like characteristics. Another strain called NIES-Brn has been maintained by randomized breeding in a closed colony to produce outbred-like characteristics. The current study aimed to characterize intermale aggressive behaviors in both strains and to identify possible factors regulating higher aggression in the hypothalamus, such as sex hormone and neuropeptide expression. Both strains displayed a common set of intermale aggressive behaviors that included pecking, grabbing, mounting, and cloacal contact behavior, although NIES-Brn quail showed significantly more grabbing, mounting, and cloacal contact behavior than did NIES-L quail. We examined sex hormone levels in the blood and diencephalon in both strains. Testosterone concentrations were significantly higher in the blood and diencephalon of NIES-Brn quail compared to NIES-L quail. We next examined gene expression in the hypothalamus of both strains using an Agilent gene expression microarray and real-time RT-PCR and found that gene expression of mesotocin (an oxytocin homologue) was significantly higher in the hypothalamus of NIES-Brn quail compared to NIES-L quail. Immunohistochemistry of the hypothalamus revealed that numbers of large cells (cell area>500μm²) expressing mesotocin were significantly higher in the NIES-Brn strain compared to the NIES-L strain. Taken together, our findings suggest that higher testosterone and mesotocin levels in the hypothalamus may be responsible for higher aggression in the NIES-Brn quail strain.

Absence of M-Ras modulates social behavior in mice

Background

The molecular mechanisms that determine social behavior are poorly understood. Pheromones play a critical role in social recognition in most animals, including mice, but how these are converted into behavioral responses is largely unknown. Here, we report that the absence of the small GTPase M-Ras affects social behavior in mice.

Results

In their interactions with other males, Mras^−/− males exhibited high levels of territorial aggression and social investigations, and increased fear-related behavior. They also showed increased mating behavior with females. Curiously, increased aggression and mating behaviors were only observed when Mras^−/− males were paired with Mras^−/− partners, but were significantly reduced when paired with wild-type (WT) mice. Since mice use pheromonal cues to identify other individuals, we explored the possibility that pheromone detection may be altered in Mras^−/− mice. Unlike WT mice, Mras^−/− did not show a preference for exploring unfamiliar urinary pheromones or unfamiliar isogenic mice. Although this could indicate that vomeronasal function and/or olfactory learning may be compromised in Mras^−/− mice, these observations were not fully consistent with the differential behavioral responses to WT and Mras^−/− interaction partners by Mras^−/− males. In addition, induction of c-fos upon pheromone exposure or in response to mating was similar in WT and Mras^−/− mice, as was the ex vivo expansion of neural progenitors with EGF. This indicated that acute pheromone detection and processing was likely intact. However, urinary metabolite profiles differed between Mras^−/− and WT males.

Conclusions

The changes in behaviors displayed by Mras^−/− mice are likely due to a complex combination of factors that may include an inherent predisposition to increased aggression and sexual behavior, and the production of distinct pheromones that could override the preference for unfamiliar social odors. Olfactory and/or social learning processes may thus be compromised in Mras^−/− mice.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-015-0209-8) contains supplementary material, which is available to authorized users.

Mapping of Genetic Factors That Elicit Intermale Aggressive Behavior on Mouse Chromosome 15: Intruder Effects and the Complex Genetic Basis

Despite high estimates of the heritability of aggressiveness, the genetic basis for individual differences in aggression remains unclear. Previously, we showed that the wild-derived mouse strain MSM/Ms (MSM) exhibits highly aggressive behaviors, and identified chromosome 15 (Chr 15) as the location of one of the genetic factors behind this escalated aggression by using a panel of consomic strains of MSM in a C57BL/6J (B6) background. To understand the genetic effect of Chr 15 derived from MSM in detail, this study examined the aggressive behavior of a Chr 15 consomic strain towards different types of opponent. Our results showed that both resident and intruder animals had to have the same MSM Chr 15 genotype in order for attack bites to increase and attack latency to be reduced, whereas there was an intruder effect of MSM Chr 15 on tail rattle behavior. To narrow down the region that contains the genetic loci involved in the aggression-eliciting effects on Chr 15, we established a panel of subconsomic strains of MSM Chr 15. Analysis of these strains suggested the existence of multiple genes that enhance and suppress aggressive behavior on Chr 15, and these loci interact in a complex way. Regression analysis successfully identified four genetic loci on Chr 15 that influence attack latency, and one genetic locus that partially elicits aggressive behaviors was narrowed down to a 4.1-Mbp region (from 68.40 Mb to 72.50 Mb) on Chr 15.

Estrogen involvement in social behavior in rodents: Rapid and long-term actions

This article is part of a Special Issue ("Estradiol and cognition"). Estrogens have repeatedly been shown to influence a wide array of social behaviors, which in rodents are predominantly olfactory-mediated. Estrogens are involved in social behavior at multiple levels of processing, from the detection and integration of socially relevant olfactory information to more complex social behaviors, including social preferences, aggression and dominance, and learning and memory for social stimuli (e.g. social recognition and social learning). Three estrogen receptors (ERs), ERα, ERβ, and the G protein-coupled ER 1 (GPER1), differently affect these behaviors. Social recognition, territorial aggression, and sexual preferences and mate choice, all requiring the integration of socially related olfactory information, seem to primarily involve ERα, with ERβ playing a lesser, modulatory role. In contrast, social learning consistently responds differently to estrogen manipulations than other social behaviors. This suggests differential ER involvement in brain regions important for specific social behaviors, such as the ventromedial and medial preoptic nuclei of the hypothalamus in social preferences and aggression, the medial amygdala and hippocampus in social recognition, and the prefrontal cortex and hippocampus in social learning. While the long-term effects of ERα and ERβ on social behavior have been extensively investigated, our knowledge of the rapid, non-genomic, effects of estrogens is more limited and suggests that they may mediate some social behaviors (e.g. social learning) differently from long-term effects. Further research is required to compare ER involvement in regulating social behavior in male and female animals, and to further elucidate the roles of the more recently described G protein-coupled ERs, both the GPER1 and the Gq-mER.

Preliminary genetic imaging study of the association between estrogen receptor-α gene polymorphisms and harsh human maternal parenting

A failure of neural changes initiated by the estrogen surge in late pregnancy to reverse the valence of infant stimuli from aversive to rewarding is associated with dysfunctional maternal behavior in nonhuman mammals. Estrogen receptor-α plays the crucial role in mediating these neural effects of estrogen priming. This preliminary study examines associations between estrogen receptor-α gene polymorphisms and human maternal behavior. Two polymorphisms were associated with human negative maternal parenting. Furthermore, hemodynamic responses in functional magnetic resonance imaging to child stimuli in neural regions associated with social cognition fully mediated the association between genetic variation and negative parenting. This suggests testable hypotheses regarding a biological pathway between genetic variants and dysfunctional human maternal parenting.

Estrogenic involvement in social learning, social recognition and pathogen avoidance

Sociality comes with specific cognitive skills that allow the proper processing of information about others (social recognition), as well as of information originating from others (social learning). Because sociality and social interactions can also facilitate the spread of infection among individuals the ability to recognize and avoid pathogen threat is also essential. We review here various studies primarily from the rodent literature supporting estrogenic involvement in the regulation of social recognition, social learning (socially acquired food preferences and mate choice copying) and the recognition and avoidance of infected and potentially infected individuals. We consider both genomic and rapid estrogenic effects involving estrogen receptors α and β, and G-protein coupled estrogen receptor 1, along with their interactions with neuropeptide systems in the processing of social stimuli and the regulation and expression of these various socially relevant behaviors.

Effects of an estrogen receptor alpha agonist on agonistic behaviour in intact and gonadectomized male and female mice

Gonadal hormones mediate both affiliative and agonistic social interactions. Research in estrogen receptor alpha (ERα) or beta (ERβ) knockout (KO) mice suggests that ERα increases and ERβ decreases male aggression, while the opposite is found for female ERαKO and ERβKO mice. Using a detailed behavioural analysis of the resident-intruder test, we have shown that the ERβ selective agonist WAY-200070 increased agonistic behaviours, such as aggressive grooming and pushing down a gonadectomized (gonadex) intruder, in gonadally intact but not gonadex male and female resident mice, while leaving attacks unaffected. The role of acute activation of ERα in agonistic behaviour in adult non-KO CD1 mice is presently unknown. The current study assesses the effects of the ERα selective agonist 1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole (PPT) on the social and agonistic responses of gonadally intact and gonadex male and female CD1 mice to a gonadex, same-sex intruder. PPT had few effects in gonadally intact mice, but seems to increase sex-typical aggression (i.e., attacks in males, other dominance-related behaviours in females) in gonadex mice. In untreated mice, we confirmed our previous findings that gonadally intact males attacked the intruder more than females, but females spent more time engaged in agonistic behaviour than males. As in our previous results, we observed that gonadex mice generally show behaviour patterns more like those of the gonadally intact opposite sex, while leaving overall levels of agonistic behaviour unaffected. Taken together, our current and previous results show that exogenous activation of ERα had no effects in gonadally intact mice, but increased sex-typical agonistic behaviour in gonadex mice, while ERβ had no effects in gonadex mice, but increased non-attack agonistic behaviour in gonadally intact animals. This suggests that, as in social recognition, ERα may be necessary for the activation of agonistic responses, while ERβ may play a modulatory role.

Positive selection shaped the convergent evolution of independently expanded kallikrein subfamilies expressed in mouse and rat saliva proteomes

We performed proteomics studies of salivas from the genome mouse (C57BL/6 strain) and the genome rat (BN/SsNHsd/Mcwi strain). Our goal was to identify salivary proteins with one or more of three characteristics that may indicate that they have been involved in adaptation: 1) rapid expansion of their gene families; 2) footprints of positive selection; and/or 3) sex-limited expression. The results of our proteomics studies allow direct comparison of the proteins expressed and their levels between the sexes of the two rodent species. Twelve members of the Mus musculus species-specific kallikrein subfamily Klk1b showed sex-limited expression in the mouse saliva proteomes. By contrast, we did not find any of the Rattus norvegicus species-specific kallikrein subfamily Klk1c proteins in male or female genome rat, nor transcripts in their submandibular glands. On the other hand, we detected expression of this family as transcripts in the submandibular glands of both sexes of Sprague-Dawley rats. Using the CODEML program in the PAML package, we demonstrate that the two rodent kallikrein subfamilies have apparently evolved rapidly under the influence of positive selection that continually remodeled the amino acid sites on the same face in the members of the subfamilies. Thus, although their kallikrein subfamily expansions were independent, this evolutionary pattern has occurred in parallel in the two rodent species, suggesting a form of convergent evolution at the molecular level. On the basis of this new data, we suggest that the previous speculative function of the species-specific rodent kallikreins as important solely in wound healing in males be investigated further. In addition to or instead of that function, we propose that their sex-limited expression, coupled with their rapid evolution may be clues to an as-yet-undetermined interaction between the sexes.

Minireview: estrogen receptor-initiated mechanisms causal to mammalian reproductive behaviors

While estrogen-facilitated changes in gene expression constitute some of the best-analyzed biochemical phenomena in the regulation of transcription, there have been at least two aspects of this topic that have led to much experimental work about estrogen actions on brain and behavior. The first task has required parsing various behavioral and neurochemical functions according to whether they depend on estrogen receptor-α or estrogen receptor-β. The second task has been the formulation of how nuclear actions of estrogens comport with membrane-initiated actions. With respect to these issues, applications of molecular endocrine approaches to lordosis behavior came first. Currently, the last in the chain of reproductive behaviors, maternal behavior, and an entire range of neural and cognitive functions even more complex in their determinants, must be analyzed using current molecular techniques. This minireview of estrogen actions on the chain of female reproductive behaviors highlights challenging new questions about estrogen actions on cells in the brain, questions that have important practical applications far beyond traditionally studied sex behaviors.

Distribution of estrogen receptor β containing cells in the brains of bacterial artificial chromosome transgenic mice

In the brain, estrogen receptor beta (ERbeta) plays important roles in autonomic functions, stress reactivity and learning and memory processes. However, understanding the function of ERbeta has been restricted by the limited availability of specific antisera, by difficulties discriminating the discrete localization of ERbeta-immunoreactivity (ir) at the light microscopic level in many brain regions and the identification of ERbeta-containing neurons in neurophysiological and molecular studies. Here, we demonstrate that a Esr2 bacterial artificial chromosome (BAC) transgenic mouse line that expresses ERbeta identified by enhanced green fluorescent protein (EGFP) overcomes these shortcomings. Throughout the brain, ERbeta-EGFP was detected in the nuclei and cytoplasm of cells, the majority of which resembled neurons. EGFP often extended into dendritic processes and could be identified either natively or following intensification of EGFP using immunolabeling. The distribution of ERbeta-EGFP cells in brain closely corresponded to that reported for ERbeta protein and mRNA. In particular, ERbeta-EGFP cells were found in autonomic brain regions (i.e., hypothalamic paraventricular nucleus, rostral ventrolateral medulla and nucleus of the solitary tract), in regions associated with anxiety and stress behaviors (i.e., bed nucleus of the stria terminalis, amygdala, periaqueductal gray, raphe and parabrachial nuclei) and in regions involved in learning and memory processes (i.e., basal forebrain, cerebral cortex and hippocampus). Additionally, dual label light and electron microscopic studies in select brain areas demonstrate that cell containing ERbeta-EGFP colocalize with both nuclear and extranuclear ERbeta-immunoreactivity. These findings support the utility of Esr2 BAC transgenic reporter mice for future studies understanding the role of ERbeta in CNS function.

Agonistic behavior in males and females: effects of an estrogen receptor beta agonist in gonadectomized and gonadally intact mice

Affiliative and agonistic social interactions are mediated by gonadal hormones. Research with estrogen receptor alpha (ERalpha) or beta (ERbeta) knockout (KO) mice show that long-term inactivation of ERalpha decreases, while inactivation of ERbeta increases, male aggression. Opposite effects were found in female alphaERKO and betaERKO mice. The role of acute activation of ERalpha or ERbeta in the agonistic responses of adult non-KO mice is unknown. We report here the effects of the ERbeta selective agonist WAY-200070 on agonistic and social behavior in gonadally intact and gonadectomized (gonadex) male and female CD-1 mice towards a gonadex, same-sex intruder. All 15min resident-intruder tests were videotaped for comprehensive behavioral analysis. Separate analyses assessed: (1) effects of WAY-200070 on each sex and gonadal condition; (2) differences between sexes, and between gonadally intact and gonadex mice, in untreated animals. Results show that in gonadally intact male and female mice, WAY-200070 increased agonistic behaviors such as pushing down the intruder and aggressive grooming, while leaving attacks unaffected. In untreated mice, males attacked more than females, and gonadex animals showed less agonistic behavior than same-sex, gonadally intact mice. Overall, our detailed behavioral analysis suggested that in gonadally intact male and female mice, ERbeta mediates patterns of agonistic behavior that are not directly involved in attacks. This suggests that specific aspects of aggressive behavior are acutely mediated by ERbeta in adult mice. Our results also showed that, in resident-intruder tests, female mice spend as much time in intrasexual agonistic interactions as males, but use agonistic behaviors that involve extremely low levels of direct attacks. This non-attack aggression in females is increased by acute activation of ERbeta. Thus, acute activation of ERbeta similarly mediates agonistic behavior in adult male and female CD-1 mice.

Conceptualizing the role of estrogens and serotonin in the development and maintenance of bulimia nervosa

Serotonergic dysregulation is thought to underlie much of the pathology in bulimia nervosa (BN). The purpose of this review is to expand the serotonergic model by incorporating specific and nonspecific contributions of estrogens to the development and maintenance of bulimic pathology in order to guide research from molecular genetics to novel therapeutics for BN. Special emphasis is given to the organizing theory of general brain arousal which allows for integration of specific and nonspecific effects of these systems on behavioral endpoints such as binge eating or purging as well as arousal states such as fear, novelty seeking, or sex. Regulation of the serotonergic system by estrogens is explored, and genetic, epigenetic, and environmental estrogen effects on bulimic pathology and risk factors are discussed. Genetic and neuroscientific research support this two-system conceptualization of BN with both contributions to the developmental and maintenance of the disorder. Implications of an estrogenic-serotonergic model of BN are discussed as well as guidelines and suggestions for future research and novel therapeutic targets.

Mechanisms underlying sexual and affiliative behaviors of mice: relation to generalized CNS arousal

The field of social neuroscience has grown dramatically in recent years and certain social responses have become amenable to mechanistic investigations. Toward that end, there has been remarkable progress in determining mechanisms for a simple sexual behavior, lordosis behavior. This work has proven that specific hormone-dependent biochemical reactions in specific parts of the mammalian brain regulate a biologically important behavior. On one hand, this sex behavior depends on underlying mechanisms of CNS arousal. On the other hand, it serves as a prototypical social behavior. The same sex hormones and the genes that encode their receptors as are involved in lordosis, also affect social recognition. Here we review evidence for a micronet of genes promoting social recognition in mice and discuss their biological roles.

Mutant mouse models: genotype-phenotype relationships to negative symptoms in schizophrenia

Negative symptoms encompass diminution in emotional expression and motivation, some of which relate to human attributes that may not be accessible readily in animals. Additionally, their refractoriness to treatment precludes therapeutic validation of putative models. This review considers critically the application of mutant mouse models to the study of the pathobiology of negative symptoms. It focuses on 4 main approaches: genes related to the pathobiology of schizophrenia, genes associated with risk for schizophrenia, neurodevelopmental-synaptic genes, and variant approaches from other areas of neurobiology. Despite rapid advances over the past several years, it is clear that we continue to face substantive challenges in applying mutant models to better understand the pathobiology of negative symptoms: the majority of evidence relates to impairments in social behavior, with only limited data relating to anhedonia and negligible data concerning avolition and other features; even for the most widely examined feature, social behavior, studies have used diverse assessments thereof; modelling must proceed in cognizance of increasing evidence that genes and pathobiologies implicated in schizophrenia overlap with other psychotic disorders, particularly bipolar disorder. Despite the caveats and challenges, several mutant lines evidence a phenotype for at least one index of social behavior. Though this may suggest superficially some shared relationship to negative symptoms, it is not yet possible to specify either the scope or the pathobiology of that relationship for any given gene. The breadth and depth of ongoing studies in mutants hold the prospect of addressing these shortcomings.

Contributions of estrogen receptor-α and estrogen receptor-ß to the regulation of behavior

Studies of the mechanisms by which estrogens influence brain function and behavior have advanced from the explication of individual hormone receptors, neural circuitry and individual gene expression. Now, we can report patterns of estrogen receptor subtype contributions to patterns of behavior. Moreover, new work demonstrates important contributions of nuclear receptor coactivator expression in the central nervous system. In this paper, our current state of knowledge is reviewed.

Genetic mapping of social interaction behavior in B6/MSM consomic mouse strains

Genetic studies are indispensable for understanding the mechanisms by which individuals develop differences in social behavior. We report genetic mapping of social interaction behavior using inter-subspecific consomic strains established from MSM/Ms (MSM) and C57BL/6J (B6) mice. Two animals of the same strain and sex, aged 10 weeks, were introduced into a novel open-field for 10 min. Social contact was detected by an automated system when the distance between the centers of the two animals became less than ~12 cm. In addition, detailed behavioral observations were made of the males. The wild-derived mouse strain MSM showed significantly longer social contact as compared to B6. Analysis of the consomic panel identified two chromosomes (Chr 6 and Chr 17) with quantitative trait loci (QTL) responsible for lengthened social contact in MSM mice and two chromosomes (Chr 9 and Chr X) with QTL that inhibited social contact. Detailed behavioral analysis of males identified four additional chromosomes associated with social interaction behavior. B6 mice that contained Chr 13 from MSM showed more genital grooming and following than the parental B6 strain, whereas the presence of Chr 8 and Chr 12 from MSM resulted in a reduction of those behaviors. Longer social sniffing was observed in Chr 4 consomic strain than in B6 mice. Although the frequency was low, aggressive behavior was observed in a few pairs from consomic strains for Chrs 4, 13, 15 and 17, as well as from MSM. The social interaction test has been used as a model to measure anxiety, but genetic correlation analysis suggested that social interaction involves different aspects of anxiety than are measured by open-field test.

Estrogen masculinizes neural pathways and sex-specific behaviors

Sex hormones are essential for neural circuit development and sex-specific behaviors. Male behaviors require both testosterone and estrogen, but it is unclear how the two hormonal pathways intersect. Circulating testosterone activates the androgen receptor (AR) and is also converted into estrogen in the brain via aromatase. We demonstrate extensive sexual dimorphism in the number and projections of aromatase-expressing neurons. The masculinization of these cells is independent of AR but can be induced in females by either testosterone or estrogen, indicating a role for aromatase in sexual differentiation of these neurons. We provide evidence suggesting that aromatase is also important in activating male-specific aggression and urine marking because these behaviors can be elicited by testosterone in males mutant for AR and in females subjected to neonatal estrogen exposure. Our results suggest that aromatization of testosterone into estrogen is important for the development and activation of neural circuits that control male territorial behaviors.

The organizational-activational hypothesis as the foundation for a unified theory of sexual differentiation of all mammalian tissues

The 1959 publication of the paper by Phoenix et al. was a major turning point in the study of sexual differentiation of the brain. That study showed that sex differences in behavior, and by extension in the brain, were permanently sexually differentiated by testosterone, a testicular secretion, during an early critical period of development. The study placed the brain together in a class with other major sexually dimorphic tissues (external genitalia and genital tracts), and proposed an integrated hormonal theory of sexual differentiation for all of these non-gonadal tissues. Since 1959, the organizational-activational theory has been amended but survives as a central concept that explains many sex differences in phenotype, in diverse tissues and at all levels of analysis from the molecular to the behavioral. In the last two decades, however, sex differences have been found that are not explained by such gonadal hormonal effects, but rather because of the primary action of genes encoded on the sex chromosomes. To integrate the classic organizational and activational effects with the more recently discovered sex chromosome effects, we propose a unified theory of sexual differentiation that applies to all mammalian tissues.

Differential effects of estrogen receptor alpha and beta specific agonists on social learning of food preferences in female mice

There is an evolutionary advantage to learning food preferences from conspecifics, as social learning allows an individual to bypass the risks associated with trial and error individual learning. The social transmission of food preferences (STFP) paradigm examines this advantage. Females in the proestrus and diestrus phases of the estrous cycle show a prolonged preference for the demonstrated food relative to estrus and ovariectomized females. Additionally, both estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta) knockout mice show impaired social recognition, which suggests that both receptors may be involved in other types of socially dependent learning, including the STFP. The present study investigated the effect of the ERalpha selective agonist PPT (1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole) and the ERbeta selective agonist WAY-200070 (7-Bromo-2-(4-hydroxyphenyl)-1,3-benzoxazol-5-ol) on the STFP. Results showed that ovariectomized (ovx) mice treated with PPT failed to learn the socially acquired preference, while WAY-200070-treated ovx mice showed a two-fold prolonged preference for the food eaten by their demonstrator. The effects of PPT on the socially acquired food preference cannot be explained by effects on the total food intake of the groups or on the type of interaction with the demonstrator mouse. The effects of WAY-200070 may be partially due to effects on Submissive Behavior. The higher WAY-200070 doses produced prolonged preferences similar to those seen previously in intact female mice during the proestrus and diestrus phases. This suggests that the estrous cycle's effects on social learning may be due to the action of ERbeta on Submissive Behavior, or to ERbeta countering that of ERalpha.

Involvement of estrogen receptor ?, ? and oxytocin in social discrimination: a detailed behavioral analysis with knockout female mice

Social recognition, processing, and retaining information about conspecific individuals is crucial for the development of normal social relationships. The neuropeptide oxytocin (OT) is necessary for social recognition in male and female mice, with its effects being modulated by estrogens in females. In previous studies, mice whose genes for the estrogen receptor-alpha (alpha-ERKO) and estrogen receptor-beta (beta-ERKO) as well as OTKO were knocked out failed to habituate to a repeatedly presented conspecific and to dishabituate when the familiar mouse is replaced by a novel animal (Choleris et al. 2003, Proc Natl Acad Sci USA 100, 6192-6197). However, a binary social discrimination assay, where animals are given a simultaneous choice between a familiar and a previously unknown individual, offers a more direct test of social recognition. Here, we used alpha-ERKO, beta-ERKO, and OTKO female mice in the binary social discrimination paradigm. Differently from their wild-type controls, when given a choice, the KO mice showed either reduced (beta-ERKO) or completely impaired (OTKO and alpha-ERKO) social discrimination. Detailed behavioral analyses indicate that all of the KO mice have reduced anxiety-related stretched approaches to the social stimulus with no overall impairment in horizontal and vertical activity, non-social investigation, and various other behaviors such as, self-grooming, digging, and inactivity. Therefore, the OT, ER-alpha, and ER-beta genes are necessary, to different degrees, for social discrimination and, thus, for the modulation of social behavior (e.g. aggression, affiliation).

Behavioral styles in European rabbits: social interactions and responses to experimental stressors

The existence and consistency of individual behavioral types in response to challenging situations is of increasing interest in behavioral biology. In our study on European rabbits (Oryctolagus cuniculus), we (1) investigated correlations between social behavior during early development and responses to experimental stressors during later life, and (2) tested for consistencies in these responses across different situations. For this, we observed juveniles living in field enclosures in early summer and recorded agonistic and positive social interactions. In autumn, the animals were (a) introduced singly into a novel environment and were (b) confronted with predator (red fox Vulpes vulpes) odor. We recorded behavioral and physiological stress responses. In addition, we evaluated the predator odor test with an independent sample of animals. These latter results showed a correlation between the animals' behavioral and physiological response: Individuals, which reacted to the presence of fox odor by low scanning rates showed a high increase in serum corticosterone challenge concentrations, whilst the levels in high scanners remained stable. Overall, we found correlations among social behavior displayed during early development and behavioral responses in the two experimental tests, however the correlations between the different traits of social behavior and the responses during the two different experimental tests were not consistent. Animals which were involved in more agonistic interactions during their early development started to explore faster when entered into the novel environment. During the second test we found that rabbits which previously showed a higher frequency of positive social behavior responded to the presence of predator odor by more scanning. Moreover, the behavioral responses during both experimental tests were not correlated: fast explorers in the novel environment test did not show a more active response during the predator odor test. Due to this lack of consistent behavioral styles across both tests we conclude that the study fails to support the existence of domain-general behavioral phenotypes in European rabbits.

Sex and estrogenic effects on coexpression of mRNAs in single ventromedial hypothalamic neurons

Regulated gene expression in single neurons can be linked to biophysical events and behavior in the case of estrogen-regulated gene expression in neurons in the ventrolateral portion of the ventromedial nucleus (VMN) of the hypothalamus. These cells are essential for lordosis behavior. What genes are coexpressed in neurons that have high levels of mRNAs for estrogen receptors (ERs)? We have been able to isolate and measure certain mRNAs from individual VMN neurons collected from rat hypothalamus. Large numbers of neurons express mRNA for ERalpha, but these neurons are not identical with the population of VMN neurons expressing the likely gene duplication product, ERbeta. An extremely high proportion of neurons expressing either ER also coexpress mRNA for the oxytocin receptor (OTR). This fact matches the known participation of oxytocin binding and signaling in sexual and affiliative behaviors. In view of data that ER and OTR can signal through PKCs, we looked at coexpression of selected PKCs in the same individual neurons. The most discriminating analysis was for triple coexpression of ERs, OTR, and each selected PKC isoform. These patterns of triple coexpression were significantly different for male vs. female VMN neurons. Further, individual neurons expressing ERalpha could distribute their signaling across the various PKC isoforms differently in different cells, whereas the reverse was not true. These findings and this methodology establish the basis for systematic linkage of the brain's hormone-sensitive signaling pathways to biophysical and behavioral mechanisms in a well studied mammalian system.