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The neuropeptide arginine vasopressin (AVP) plays significant roles in maintaining homeostasis and regulating social behavior. In vaginally delivered neonates, a surge of AVP is released into the bloodstream at levels exceeding release during life-threatening conditions such as hemorrhagic shock. It is currently unknown where the potential sites of action are in the neonate for these robust levels of circulating AVP at birth. The purpose of this study is to identify the location of AVP receptor 1a (AVPR1A) sites as potential peripheral targets of AVP in the neonatal mouse. RT-qPCR analysis of a sampling of tissues from the head demonstrated the presence of Avpr1a mRNA, suggesting local peripheral translation. Using competitive autoradiography in wildtype (WT) and AVPR1A knockout (KO) postnatal day 0 (P0) male and female mice on a C57BL/6J background, specific AVPR1A ligand binding was observed in the neonatal mouse periphery in sensory tissues of the head (eyes, ears, various oronasal regions), bone, spinal cord, adrenal cortex, and the uro-anogenital region in the neonatal AVPR1A WT mouse, as it was significantly reduced or absent in the control samples (AVPR1A KO and competition). AVPR1A throughout the neonatal periphery suggest roles for AVP in modulating peripheral physiology and development of the neonate.

Prader-Willi syndrome (PWS) is caused by deficient expression of the paternal copy of several contiguous genes on chromosome 15q11-q13 and affects multiple organ systems in the body, including the nervous system. Feeding and suckling deficits in infants with PWS are replaced with excessive feeding and obesity in childhood through adulthood. Clinical trials using intranasal oxytocin (OXT) show promise to improve feeding deficits in infants with PWS. The mechanism and location of action of exogenous OXT are unknown. We have recently shown in neonatal mice that OXT receptors (OXTR) are present in several regions of the face with direct roles in feeding. Here we show that the trigeminal ganglion, which provides sensory innervation to the face, is a rich source of Oxtr and a site of cellular co-expression with PWS gene transcripts. We also quantified OXTR ligand binding in mice deficient in Magel2, a PWS gene, within the trigeminal ganglion and regions that are anatomically relevant to feeding behavior and innervated by the trigeminal ganglion including the lateral periodontium, rostral periodontium, tongue, olfactory epithelium, whisker pads and brainstem. We found that peripheral OXTR ligand binding in the head is mostly intact in Magel2-deficient mice, although it is reduced in the lateral periodontium (gums) of neonatal Magel2-deficient mice compared to wild-type controls. These data suggest that OXT via orofacial OXTR may play a peripheral role to modulate sensory-motor reflexes necessary for suckling and may be part of the mechanism by which intranasal OXT shows promise for therapeutic benefit in PWS.

Social behaviors are foundational to society and quality of life while social behavior extremes are core symptoms in a variety of psychopathologies and developmental disabilities. Oxytocin (OXT) is a neuroactive hormone that regulates social behaviors through its receptor (OXTR), with all previously identified social behavior effects attributed to the central nervous system, which has developmental origins in the neural tube. However, OXTR are also present in neural crest-derived tissue including sensory ganglia of the peripheral nervous system. Avil encodes for the actin-binding protein ADVILLIN, is expressed in neural crest-derived cells, and was therefore used as a target in this study to knock out OXTR expression in neural-crest derived cells. Here, we tested if OXTRs specifically expressed in Avil positive neural crest-derived cells are necessary for species-typical adult social behaviors using a Cre-LoxP strategy. Genetically modified male and female mice lacking OXTR in Avil expressing cells (OXTRAvil KO) were tested for sociability and preference for social novelty. Males were also tested for resident intruder aggression. OXTRAvil KO males and females had reduced sociability compared to OXTRAvil WT controls. Additionally, OXTRAvil KO males had increased aggressive behaviors compared to controls. These data indicate that OXTRs in cells of neural crest origin are important regulators of typical social behaviors in C57BL/6J adult male and female mice and point to needed directions of future research.

Summary Spontaneous network activity shapes emerging neuronal circuits during early brain development prior to sensory perception. However, how neuromodulation influences this activity is not fully understood. Here, we report that the neuromodulator oxytocin differentially shapes spontaneous activity patterns across sensory cortices. In vivo, oxytocin strongly decreased the frequency and pairwise correlations of spontaneous activity events in the primary visual cortex (V1), but it did not affect the frequency of spontaneous network events in the somatosensory cortex (S1). Patch-clamp recordings in slices and RNAscope showed that oxytocin affects S1 excitatory and inhibitory neurons similarly, whereas in V1, oxytocin targets only inhibitory neurons. Somatostatin-positive (SST+) interneurons expressed the oxytocin receptor and were activated by oxytocin in V1. Accordingly, pharmacogenetic silencing of V1 SST+ interneurons fully blocked oxytocin’s effect on inhibition in vitro as well its effect on spontaneous activity patterns in vivo. Thus, oxytocin decreases the excitatory/inhibitory (E/I) ratio by recruiting SST+ interneurons and modulates specific features of V1 spontaneous activity patterns that are crucial for the wiring and refining of developing sensory circuits., Graphical Abstract, Highlights • Oxytocin modulates spontaneous activity event patterns in the developing V1 • Oxytocin increases inhibition by activating somatostatin+ interneurons • SST+ neuron activity reduces event frequency and correlations, but not amplitude • In S1, oxytocin increases excitation and inhibition and does not modulate frequency, Maldonado et al. uncover oxytocin’s role in developing sensory cortices. In vivo, they show that oxytocin decreases the frequency and correlations of spontaneous activity patterns in V1 by specifically activating somatostatin+ interneurons. In S1, oxytocin increases both excitation and inhibition and does not affect spontaneous activity frequency.

The oxytocin receptor (OTR) plays critical roles in social behavior development. Despite its significance, brain-wide quantitative understanding of OTR expression remains limited in postnatally developing brains. Here, we develop postnatal 3D template brains to register whole brain images with cellular resolution to systematically quantify OTR cell densities. We utilize fluorescent reporter mice (Otrvenus/+) and find that cortical regions show temporally and spatially heterogeneous patterns with transient postnatal OTR expression without cell death. Cortical OTR cells are largely glutamatergic neurons with the exception of cells in layer 6b. Subcortical regions show similar temporal regulation except the hypothalamus and two hypothalamic nuclei display sexually dimorphic OTR expression. Lack of OTR expression correlates with reduced dendritic spine densities in selected cortical regions of developing brains. Lastly, we create a website to visualize our high-resolution imaging data. In summary, our research provides a comprehensive resource for postnatal OTR expression in the mouse brain., The oxytocin receptor plays an important role in establishing mature neural circuits for social behavior during the early postnatal period. Here, the authors develop digital reference brains for different postnatal ages and provide a quantitative brain-wide map of oxytocin receptor expression in early postnatal and adult mouse brains.

The oxytocin receptor (OXTR) has been observed in the periphery of neonatal C57BL/6J mice (Mus musculus), including facial regions and the anogenital area. In those studies, ligand specificity was confirmed with a congenital OXTR knockout mouse as well as competitive binding techniques. The aim of this study was to determine if OXTR is present in the same peripheral sites in the neonatal prairie vole (Microtus ochrogaster) for cross-species comparisons. Receptor autoradiography was performed on 20 μm sagittal sections of whole postnatal day 0 (P0) male and female prairie voles using the 125iodinated-ornithine vasotocin ([125I]-OVTA) radioligand. A competition binding assay was used to assess the selectivity of [125I]-OVTA for peripheral OXTR. Radioactive ligand (0.05 nM [125I]-OVTA) was competed against concentrations of 0 and 1000 nM excess unlabeled oxytocin (OXT). Previously identified regions of significant OXTR ligand binding in the mouse were analyzed for comparison: rostral and lateral periodontium, olfactory epithelium, ciliary bodies of the eye, whisker pads, adrenal gland, and anogenital area. We also evaluated the liver and scapular brown adipose tissue, which displayed strong but non-specific signal on film in mice. While there were some areas that showed conserved OXTR ligand binding in the prairie vole (e.g., ciliary body of the eye and the anogenital area), areas showing OXTR ligand binding in the neonatal prairie vole were not identical to OXTR ligand binding in the periphery of the C57BL/6J neonatal mouse. Further, some of the regions measured in the prairie vole suggest sex differences in OXTR ligand binding. Collectively, as is well-established in the central nervous system, these data indicate that patterns of OXTR ligand binding in the infant periphery are species-specific.

Parental care and sensory stimulation are critical environmental factors that influence oxytocin (OXT) and its receptor (OXTR). Because developmental Oxt mRNA expression is enhanced by sensory-rich early life experience and reduced by sensory deprivation, we predicted that compared to wild-type (WT) littermates, mice with congenital loss of OXTR (OXTR KO), as a genetically induced deprivation, would show impaired Oxt mRNA expression in the offspring hypothalamus during development. Oxt mRNA levels of male and female OXTR KO mice were not different from WT littermates from postnatal day (P)0 to P6, although, by P8, OXTR KO showed significantly decreased Oxt mRNA expression in the hypothalamus compared to WT littermates. At P14, male and female OXTR KO mice had significantly decreased Oxt mRNA expression specifically in the paraventricular nucleus (PVN), but not the supraoptic nucleus (SON), compared to WT littermates. We investigated whether this effect persisted in adulthood (P90) and found a significant genotype by sex interaction where male OXTR KO mice displayed a reduction in Oxt expression specific to the PVN compared to male WT littermates. By contrast, male and female OXTR KO adults had increased Oxt mRNA levels in the SON. These findings suggest that OXTR plays a role in developmental Oxt mRNA expression with sex by genotype interactions apparent at adulthood. We then measured OXT and neural activation in the PVN and SON at P14. We observed more OXT-immunoreactive cells in the PVN of OXTR KO mice but significantly fewer c-Fos immunoreactive cells. There were no genotype differences in immunoreactivity for OXT and no c-Fos activity in the SON at P14. Combined, these data suggest that OXTR WT P14 mice have more PVN activity and are more likely to release OXT than OXTR KO mice. Future experiments are warranted to understand which OXTR-expressing neural circuits modulate the development of the PVN oxytocin system.

Oxytocin (OXT) signaling through the OXT receptor plays a significant role in a variety of physiological processes throughout the lifespan. OXT's effects depend on the tissue distribution of the receptor. This tissue specificity is dynamic and changes across development, and also varies with sex, experience, and species. The purpose of this review is to highlight these themes with examples from several life stages and several species. Important knowledge gaps will also be emphasized. Understanding the effective sites of action for OXT via its receptor will help refine hypotheses about the roles of this important neuropeptide in the experience-dependent development and expression of species-typical social behavior. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 143-157, 2017.

Oxytocin (OXT) regulates adult social behavior and has been implicated in its development. Because mammalian milk contains OXT and we have recently identified OXT receptors (OXTR) in the face and oronasal cavity of pre-weaning mice, we hypothesize that orally applied OXT may impact brain activity and acute behavior in developing mice. Oral OXT may have effects in the absence of sensory stimulation or perhaps by modulating sensory input, such as whisker stimulation. The present study investigates the acute c-Fos response in the paraventricular nucleus of the hypothalamus (PVN) and along whisker sensory processing brain regions (trigeminothalamocortical circuit) to orally applied OXT, compared to saline, with and without whisker stimulation in postnatal day (P) 14 and P21 male and female mice. Acute behavioral responses were also quantified after oral OXT with whisker stimulation in a non-social context. Oral OXT with and without whisker stimulation increased c-Fos activity in the PVN of males and decreased c-Fos in the ventroposterior medial thalamus in both males and females compared to saline. Additionally, oral OXT with whisker stimulation decreased c-Fos activity across whisker sensory processing brain regions in males and females and decreased c-Fos activity in the trigeminal motor nucleus of females. Lastly, oral OXT with whisker stimulation increased males' locomotor behavior and decreased females' oromotor behavior compared to saline-treated controls. These data indicate that orally applied OXT has acute brain and behavioral effects on developing mice. OXT-modulated sensory signals may bias brain and behavior development toward the social world.

Sleep is critical for proper sensory and social development in young prairie voles, an affiliative and monogamous rodent species., Across mammals, juveniles sleep more than adults, with rapid eye movement (REM) sleep at a lifetime maximum early in life. One function of REM sleep may be to facilitate brain development of complex behaviors. Here, we applied 1 week of early-life sleep disruption (ELSD) in prairie voles (Microtus ochrogaster), a highly social rodent species that forms lifelong pair bonds. Electroencephalographic recordings from juvenile voles during ELSD revealed decreased REM sleep and reduced γ power compared to baseline. ELSD impaired pair bond formation and altered object preference in adulthood. Furthermore, ELSD increased GABAergic parvalbumin immunoreactivity in the primary somatosensory cortex in adulthood, a brain region relevant to both affected behaviors. We propose that, early in life, sleep is crucial for tuning inhibitory neural circuits and the development of species-typical affiliative social behavior.

Arginine-vasopressin (AVP) and the vasopressin 1a receptor (V1aR) modulate social behavior and learning and memory in adult animals. Both functions depend upon the normal emergence of the balance of excitation and inhibition (E/I balance) in the neocortex. Here, we tested the hypothesis that V1aR signaling and E/I balance converge through the influence of the neuropeptide on interneuron number achieved in the neocortex. Postnatal mapping of forebrain V1aR binding in male and female mice revealed a transient expression of high levels of receptor in the neocortex and hippocampus in the second and third post-natal weeks. Receptor binding levels in these cortical structures fell dramatically in the adult, maintaining high levels of expression subcortically. Surprisingly, we observed sex differences in the number of calbindin interneurons, and a contribution of V1aR to the number of parvalbumin-immunoreactive neurons in the adult mouse neocortex. These data suggest that individual differences in developmentally transient V1aR signaling and even sex may alter the development of E/I balance in the neocortex, with long-lasting influence on information processing.

The neuronal transcription splicing factor, A2BP1, has been implicated in a variety of neurodevelopmental disorders; however, the role of A2BP1 in brain development and gene regulatory function remains to be explicated. Here, we map A2bp1 gene expression, focusing on the developing forebrain of the C57BL6J mouse. Early in forebrain development, A2bp1 expression is highly reminiscent of the expression of genes marking postmitotic GABAergic cells emanating from the ventral telencephalon during migration to the dorsal pallium. Ventral pallial expression remains low after the migratory period. Broader dorsal pallial expression becomes more evident late prenatally and early postnatally. This is paralleled by dense, restricted expression in the ventrobasal dorsal thalamic complex and mid-hypothalamic region. Outside of the forebrain, there is significant expression in motor pathways. These data indicate that A2BP1 mutations may clinically affect very selective forebrain neuron types from early periods of development.

Comparative studies in voles have suggested that a polymorphic microsatellite upstream of the Avpr1a locus contributes to the evolution of monogamy. A recent study challenged this hypothesis by reporting that there is no relationship between microsatellite structure and monogamy in 21 vole species. Although the study demonstrates that the microsatellite is not a universal genetic switch that determines mating strategy, the findings do not preclude a substantial role for Avpr1a in regulating social behaviors associated with monogamy.

Repetitive microsatellites mutate at relatively high rates and may contribute to the rapid evolution of species-typical traits. We show that individual alleles of a repetitive polymorphic microsatellite in the 5′ region of the prairie vole vasopressin 1a receptor ( avpr1a ) gene modify gene expression in vitro. In vivo, we observe that this regulatory polymorphism predicts both individual differences in receptor distribution patterns and socio-behavioral traits. These data suggest that individual differences in gene expression patterns may be conferred via polymorphic microsatellites in the cis-regulatory regions of genes and may contribute to normal variation in behavioral traits.

Arginine vasopressin modulates pairbond formation in the monogamous prairie vole (Microtus ochrogaster). Our laboratory has investigated the genetic and neural mechanisms by which vasopressin and its V1a receptor (V1aR) regulate social attachment between mates. Non-monogamous vole species show strikingly different distribution patterns of brain V1aR expression compared to monogamous species, and these patterns are thought to arise from species differences in the respective promoter sequences of the V1aR gene. Individual differences in prairie vole V1aR patterns may also reflect individual differences in promoter sequences. Pharmacological and genetic manipulation of the specific brain regions that express V1aR in the 'monogamous pattern' allows multilevel examination of the neural circuits that underlie pairbond formation in monogamous species. For example, V1aR are expressed in brain regions involved in reward circuitry in monogamous vole species and have been implicated in pairbonding. V1aR are also highly expressed in regions implicated in the olfactory processing of sociosexual behaviour. We hypothesize that both circuits of reward and olfactory memory underlie the cognitive mechanisms that control pairbonding. When used in conjuction, genetic and cellular analyses of a complex social behaviour can provide a coherent framework with which to examine the role of the vasopressin system in species evolution and neural control of behaviour.

Instability in highly repetitive microsatellite DNA located in the regulatory regions of genes may be a major factor producing diversity in both region-specific gene expression and the resulting phenotypes. Polymorphisms in promoter regions affecting expression of genes involved in regulating behaviour may play a role in generating individual variation in behaviour, including psychopathologies in humans, and probably are also important for the evolution of behaviour. Here we discuss the prairie vole vasopressin V1a receptor gene as a model that may be useful for understanding the evolution of promoter sequences and the relationship between gene sequence, expression and behavioural phenotype.

From a biologist's perspective, social behavior includes any behavior that involves at least two actors. By this definition, social behavior can include aggregation in slime molds, the colony structure of the eusocial insects, or the coordinated efforts of humans across vast distances to successfully land on the moon. The diversity of this range of behavior shares one driving force: natural selection. While natural selection acts at the level of phenotype (e.g., morphology, metabolism, behavior) the ultimate unit of natural selection is the gene contained in DNA-the object of inheritance. The relationship between DNA and social behavior is uncovered in the field of sociogenomics, defined as the mechanistic study of genes, gene products, and gene × gene interaction networks supporting emergent social behaviors.

Family relationships help shape species-typical social and emotional development, but our understanding of how this shaping occurs is still relatively limited. Prairie voles are a socially monogamous and biparental species that is well situated to complement traditional animal models, such as rats and mice, in investigating the effects of family experience. In this series of studies, we aimed to test hypotheses relating to how prairie vole families function under undisturbed, standard laboratory conditions. In the first study, we compared the parental behavior of primiparous biparental (BP) and single-mother (SM) prairie vole family units for 12 postnatal days and then tested for sex differences, behavioral coordination, and family structure effects. Under BP conditions, nest attendance was coordinated and shared equally by both sexes, while pup-directed and partner-directed licking and grooming (LG) were coordinated in a sex and social-context-dependent manner. Contrary to our expectations, SMs showed no evidence of strong parental compensation in response to the lack of the father, indicating a minimal effect of family structure on maternal behavior but a large effect on pup care. In the second study, we examined the effects of these BP and SM rearing conditions on family dynamics in the next generation and found that SM-reared adult parents exhibited lower rates of pup-directed LG in comparison to BP-reared counterparts. Situated in the context of human family dynamics and psychology, these results suggest that the study in prairie voles may help improve our understanding of family systems and how perturbations to these systems can affect adults and offspring.

Background In an effort to identify genes that specify the mammalian forebrain, we used a comparative approach to identify mouse homologs of transcription factors expressed in developing Caenorhabditis elegans GABAergic neurons. A cell-specific microarray profiling study revealed a set of transcription factors that are highly expressed in embryonic C. elegans GABAergic neurons. Results Bioinformatic analyses identified mouse protein homologs of these selected transcripts and their expression pattern was mapped in the mouse embryonic forebrain by in situ hybridization. A review of human homologs indicates several of these genes are potential candidates in neurodevelopmental disorders. Conclusions Our comparative approach has revealed several novel candidates that may serve as future targets for studies of mammalian forebrain development.

Background The arginine vasopressin V1a receptor (V1aR) modulates social cognition and behavior in a wide variety of species. Variation in a repetitive microsatellite element in the 5' flanking region of the V1aR gene (AVPR1A) in rodents has been associated with variation in brain V1aR expression and in social behavior. In humans, the 5' flanking region of AVPR1A contains a tandem duplication of two ~350 bp, microsatellite-containing elements located approximately 3.5 kb upstream of the transcription start site. The first block, referred to as DupA, contains a polymorphic (GT)25 microsatellite; the second block, DupB, has a complex (CT)4-(TT)-(CT)8-(GT)24 polymorphic motif, known as RS3. Polymorphisms in RS3 have been associated with variation in sociobehavioral traits in humans, including autism spectrum disorders. Thus, evolution of these regions may have contributed to variation in social behavior in primates. We examined the structure of these regions in six ape, six monkey, and one prosimian species. Results Both tandem repeat blocks are present upstream of the AVPR1A coding region in five of the ape species we investigated, while monkeys have only one copy of this region. As in humans, the microsatellites within DupA and DupB are polymorphic in many primate species. Furthermore, both single (lacking DupB) and duplicated alleles (containing both DupA and DupB) are present in chimpanzee (Pan troglodytes) populations with allele frequencies of 0.795 and 0.205 for the single and duplicated alleles, respectively, based on the analysis of 47 wild-caught individuals. Finally, a phylogenetic reconstruction suggests two alternate evolutionary histories for this locus. Conclusion There is no obvious relationship between the presence of the RS3 duplication and social organization in primates. However, polymorphisms identified in some species may be useful in future genetic association studies. In particular, the presence of both single and duplicated alleles in chimpanzees provides a unique opportunity to assess the functional role of this duplication in contributing to variation in social behavior in primates. While our initial studies show no signs of directional selection on this locus in chimps, pharmacological and genetic association studies support a potential role for this region in influencing V1aR expression and social behavior.

Most mammalian species are nonmonogamous: the female alone cares for the young and males and females do not share nest sites. Within the genus Microtus, there exists ample diversity in social structure for neuroethological and neurobiological investigation. Prairie voles (Microtus ochrogaster) are socially monogamous: both the males and females contribute to care of the young within a shared nest site as a breeding pair through multiple breeding seasons. Closely related species such as the montane (M. montanus) and meadow (M. pennsylvanicus) voles do not typically show these behaviors. Over a decade of research has demonstrated that species differences in neuropeptide systems play significant roles in the behavioral divergence of these species. In particular, species differences in regional gene expression patterns of neuropeptide receptors in the brain mediate some of the behavioral traits associated with the divergence in social structure. Differences in gene expression patterns of a key gene in mediating social behavior, the arginine vasopressin 1a receptor (avpr1a), appear to be due to species divergence in a repeat locus in the 5' regulatory region of avpr1a. This highly repetitive locus is prone to expansion and contraction over relatively short evolutionary timescales and may give rise to the rapid evolution of sociobehavioral traits.

Understanding the neurobiological substrates regulating normal social behaviours may provide valuable insights in human behaviour, including developmental disorders such as autism that are characterized by pervasive deficits in social behaviour. Here, we review the literature which suggests that the neuropeptides oxytocin and vasopressin play critical roles in modulating social behaviours, with a focus on their role in the regulation of social bonding in monogamous rodents. Oxytocin and vasopressin contribute to a wide variety of social behaviours, including social recognition, communication, parental care, territorial aggression and social bonding. The effects of these two neuropeptides are species-specific and depend on species-specific receptor distributions in the brain. Comparative studies in voles with divergent social structures have revealed some of the neural and genetic mechanisms of social-bonding behaviour. Prairie voles are socially monogamous; males and females form long-term pair bonds, establish a nest site and rear their offspring together. In contrast, montane and meadow voles do not form a bond with a mate and only the females take part in rearing the young. Species differences in the density of receptors for oxytocin and vasopressin in ventral forebrain reward circuitry differentially reinforce social-bonding behaviour in the two species. High levels of oxytocin receptor (OTR) in the nucleus accumbens and high levels of vasopressin 1a receptor (V1aR) in the ventral pallidum contribute to monogamous social structure in the prairie vole. While little is known about the genetic factors contributing to species-differences in OTR distribution, the species-specific distribution pattern of the V1aR is determined in part by a species-specific repetitive element, or ‘microsatellite’, in the 5′ regulatory region of the gene encoding V1aR ( avpr1a ). This microsatellite is highly expanded in the prairie vole (as well as the monogamous pine vole) compared to a very short version in the promiscuous montane and meadow voles. These species differences in microsatellite sequence are sufficient to change gene expression in cell culture. Within the prairie vole species, intraspecific variation in the microsatellite also modulates gene expression in vitro as well as receptor distribution patterns in vivo and influences the probability of social approach and bonding behaviour. Similar genetic variation in the human AVPR1A may contribute to variations in human social behaviour, including extremes outside the normal range of behaviour and those found in autism spectrum disorders. In sum, comparative studies in pair-bonding rodents have revealed neural and genetic mechanisms contributing to social-bonding behaviour. These studies have generated testable hypotheses regarding the motivational systems and underlying molecular neurobiology involved in social engagement and social bond formation that may have important implications for the core social deficits characterizing autism spectrum disorders.

Vasopressin regulates complex behaviors such as anxiety, parenting, social engagement and attachment and aggression in a species-specific manner. The capacity of vasopressin to modulate these behaviors is thought to depend on the species-specific distribution patterns of vasopressin 1a receptors (V1aRs) in the brain. There is considerable individual variation in the pattern of V1aR binding in the brains of the prairie vole species, Microtus ochrogaster. We hypothesize that this individual variability in V1aR expression levels is associated with individual variation in a polymorphic microsatellite in the 5' regulatory region of the prairie vole v1ar gene. Additionally, we hypothesize that individual variation in V1aR expression contributes to individual variation in vasopressin-dependent behaviors. To test these hypotheses, we first screened 20 adult male prairie voles for behavioral variation using tests that measure anxiety-related and social behaviors. We then assessed the brains of those animals for V1aR variability with receptor autoradiography and used polymerase chain reaction to genotype the same animals for the length of their 5' microsatellite polymorphism in the v1ar gene. In this report, we describe the results of this discovery-based experimental approach to identify potential gene, brain and behavior interrelationships. The analysis reveals that V1aR levels, in some but not all brain regions, are associated with microsatellite length and that V1aR levels in those and other brain regions correlate with anxiety-related and social behaviors. These results generate novel hypotheses regarding neural control of anxiety-related and social behaviors and yield insight into potential mechanisms by which non-coding gene polymorphisms may influence behavioral traits.

Forebrain vasopressin/vasotocin systems regulate a diverse set of complex social behaviors in a species-specific manner. Among mammals, vasopressin gene sequences and peptide distributions in the brain are highly conserved across species. In contrast, vasopressin V1a receptors (V1aR) are conserved at the protein level, but not at the level of gene structure or neuroanatomical distribution of the receptor. Here, we examine the functional role of a microsatellite segment in the 5' region of V1aR that differs significantly between monogamous and nonmonogamous vole species with divergent V1aR expression patterns. Using luciferase reporter assays, we demonstrate that this microsatellite plays a significant role in transcriptional regulation in a cell-type-specific manner. These results suggest that significant evolutionary changes in social behavior can occur through variation in regulatory regions of genes already involved in social behavior.