Zuoxin Wang - US grants

The major goal of the proposed research is to analyze the neurochemical substrates underlying pair bonding formation and social attachment in a monogamous rodent, the prairie vole (Microtus ochrogaster). Pair bonding formation is a behavioral characteristic of monogamous mammals such as prairie voles, and is rare in polygynous species such as montane voles (M. montanus) and meadow voles (M. pennsylvanicus) (19). The development of partner preferences and selective aggression toward strangers is used here as an operational definition of a pair bonding. Previous research has implicated arginine vasopressin (AVP) in the appearance of both partner preferences and selective aggression in male prairie voles (45). However, such effects have only been examined in males, and the specific brain areas in which AVP has influences on pair bonding have not been identified, since AVP was infused into the lateral ventricle. Sex differences exist in the expression of the behavioral characteristics of monogamy in the central AVP pathways, and mating-induced activity of these pathways in prairie voles (2,3,38). The propose research will compare male and female prairie voles to examine their behavioral differences in the effects of AVP in specific brain areas.

DESCRIPTION (provided by applicant): The transition to parenthood is a major life event associated with changes in physiological and psychosocial functioning that can have a profound impact on mental health. Although research on this topic has traditionally focused on women, a small but growing number of studies have investigated the transition to parenthood in men. Men, like women, demonstrate an early and strong motivation to care for their infants/children and to form strong, rewarding attachments to them. Fatherhood can influence paternal mental health, and although it typically results in positive outcomes, it has been found to precipitate negative ones (i.e., postnatal depression and paternal psychosis). Further, the disruption of father-child interactions/attachments that results from paternal depression or loss of paternal custody after divorce has been consistently associated with decreased physical health and increased psychological distress in fathers. Indeed, paternal involvement in childcare has become increasingly recognized as equally important as maternal influences for child development and health as well as for the prevention and effective treatment of problem behaviors such as anxiety, attention- deficit/hyperactivity disorder (ADHD), substance use, and criminal behavior. Our knowledge about the neurobiology of parental behavior is almost exclusively derived from studies of maternal behavior, mainly because only ~3-5% of mammalian species display paternal behavior, and thus, an animal model has not yet been fully developed. In recent years, the socially monogamous prairie vole (Microtus ochrogaster) has emerged as an excellent animal model to study the neurobiology of complex social behaviors especially pair bonding behavior. As male prairie voles also display spontaneous paternal behavior and this behavior can be influenced by prior social experience with a female or by pharmacological manipulation of neurotransmitters including dopamine (DA), this animal model may provide an opportunity to study the neurobiology of paternal behavior. In this application, we will use male prairie voles as an animal model to test the hypothesis that the mesolimbic DA system regulates paternal behavior in a brain region-, receptor-, and behavior- specific manner. We will first compare paternal behaviors in male voles that have different social experiences with a female to establish correlations between variations of paternal behaviors and the level of DA marker expression in the brain. We will then examine changes of neuronal activation in DA-producing cells as well as changes in DA content, release, and receptor expression in selected brain areas during paternal behavior. Finally, we will pharmacologically manipulate DA receptors or the intracellular signaling cascades to reveal the functional role of central DA in paternal behavior. Together, data from these studies will shed light on the DA regulation of paternal behavior and firmly establish the prairie vole model for the study of paternal behavior. This, in turn, will facilitate the investigation of the neurobiology of paternal behavior - a scienific question that has been understudied despite its high translational value for human health.

DESCRIPTION (provided by applicant): In addition to the dentate gyrus of the hippocampus (DG) and the anterior portion of the subventricular zone (SVZ) , newly proliferated cells are found in other brain areas, including the amygdala--an area implicated in many physiological and behavioral functions. In our recent study in female prairie voles (Microtus ochrogaster), cells labeled by a proliferation marker, 5-bromo-2'-deoxyuridine (BrdU), were found in the amygdala, and male exposure and mating induced an enduring increase in the number of BrdU labeled cells in the amygdala. As male exposure and mating induce social attachment between female and male prairie voles, and the amygdala is important for the social attachment formation, we hypothesize that the stimuli associated with male exposure increase the number of newly proliferated cells in the amygdala, which, in turn, play a functional role in social attachment formation in female prairie voles. To test this hypothesis, we first study the effects of stimuli associated with male-exposure, such as an increased level of estrogen and mating behavior, on cell proliferation and cell death in the amygdala of female prairie voles. Thereafter, we treat animals with an anti-mitotic drug in general or site-specifically into the amygdala to examine the effects on cell proliferation and social attachment. These data will not only broaden our understanding of the functional significance of newly proliferated cells in general, but also provide valuable information regarding involvement of new cells of the amygdala in social attachment formation in particular.

DESCRIPTION (provided by applicant): It is believed that drugs of abuse usurp neural circuitry that initially evolved to mediate behavioral processes essential for fitness. Therefore, the take over of this circuitry by drugs of abuse usually exerts powerful control over the behavior and this is a tremendous problem for many humans. One important factor contributing to drug abuse is social environment. It has been suggested that social attachments formed in adulthood may have significant impact on drug addictions. Unfortunately, investigation into this topic is very limited partially because the vast majority of addiction research is conducted on traditional laboratory rats and mice that do not form adult-adult social attachments. Here we propose a novel line of research using a unique animal model to address fundamental questions regarding the interaction of social and drug reward and the underlying neural mechanisms. The monogamous prairie vole (Microtus ochrogaster) displays mating-induced pair bonding between mates, and this behavior is mediated by dopamine (DA) in the nucleus accumbens (NAcc). Recently, we also found that the prairie vole displays amphetamine (AMPH)-induced conditioned place preference (CPP) and pre-treatment of the DA receptor antagonist blocked this behavior. As natural reward and maladaptive drug reward are both regulated by DA, we hypothesized that these overlapping neural mechanisms will result in behavioral and neurobiological interactions between pair bonding and drug addiction. Here, we propose four studies by taking advantage of the vole model to systematically address interactions between pair bonding and drug reward and to study NAcc DA involvement in the regulation of such interactions. In Specific Aim 1, we will firmly establish the vole model for drug reward by performing detailed dose response curves for AMPH induced CPP and behavioral sensitization. In Specific Aim 2, we will examine NAcc DA involvement in AMPH reward. In Specific Aim 3, we will study behavioral interactions between pair bonding and AMPH reward. In Specific Aim 4, we will investigate the role of NAcc DA in the regulation of interactions between pair bonding and AMPH reward. Successful completion of these studies will further our understanding of behavioral and neurobiological interactions between social and drug reward, and such findings will have the potential to facilitate behavioral and neuropharmacological interventions that may aid addiction prevention.

DESCRIPTION (provided by applicant): Social attachments are a vital part of healthy human behavior and an inability to form such attachments is regarded as a symptom of mental disorders such as schizophrenia and autism. Studying the mechanisms underlying social attachment requires an animal model that displays behaviors similar to that of human social attachment. Prairie voles (Microtus ochrogaster) have become an important model for the study of the neurobiology of social attachment. In the field, male and female prairie voles form long-term bonds and share a nest throughout the breeding season. Such a breeding pair typically remains together until one animal dies. For prairie voles, it has been demonstrated that 24 h of mating reliably results in partner preference formation, whereas 6 h of cohabitation in the absence of mating does not induce this behavior. Given that mating in prairie voles induces neuroadaptations that eventually lead to bonding, we propose here to investigate whether mating induced social bonding has an underlying epigenetic basis. Our preliminary data support this hypothesis. PUBLIC HEALTH RELEVANCE: Prairie voles have become an important model for the study of the neurobiology of social attachment. Given that mating in prairie voles induces adaptations in specific brain regions that eventually lead to bonding, we propose in this proposal to investigate some of mechanisms that underlie the development of social bonding in prairie voles. Understanding the mechanisms of social bonding is very relevant to understanding some psychopathologies like autism and schizophrenia.

DESCRIPTION (provided by applicant): Adult-generated cells are found in the dentate gyrus (DG) of the hippocampus and the subventricular zone (SVZ) of the rostral lateral ventricle in mammalian brains. Scientists have focused on these two brain areas to characterize the factors mediating adult neurogenesis, determine the phenotypes of the new cells, and reveal their potential functional significance. While new cells are also found in several other brain areas, little is known about the morphological characteristics, neurochemical phenotypes, and functions of these new cells. In this proposal, we focus on the amygdala - a brain area which is important for sensory processing, information integration, and the modulation of a variety of physiological and behavioral functions, and which contains adult-generated cells but has received little attention in the neurogenesis field. We will use the socially monogamous female prairie voles (Microtus ochrogaster) as our model system as the vole's amygdala contained adult-generated cells, their rates of proliferation were facilitated by social interactions and diminished by social isolation, and treatment of an antimitotic drug reduced new neurons in the amygdala and inhibited social attachment formation. Our working hypothesis is that social/chemosensory stimuli from a conspecific affect amygdala neurogenesis in a stimulus-, time- and area-specific manner, adult-generated amygdala neurons integrate into the existing neural circuitry, express certain neurochemical phenotypes, and play a functional role in mediating social behavior. To test this hypothesis, we will focus on the amygdala to (1) examine the role of chemosensory stimuli in cell proliferation, (2) reveal the critical period for such social/chemosensory experience to enhance cell survival, (3) determine the neuromorphological and neurochemical characteristics of these new cells, (4) and examine the role of new amygdala cells in social behavior. Data from this study will shed light into amygdala adult neurogenesis and provide a starting point for the investigation of the amygdala neurogenic potential to be used as treatment for neurodegenerative-related amygdala deficits.

PROJECT ABSTRACT Social attachments are a vital part of healthy human behavior and an inability to form such attachments is regarded as a symptom of mental disorders such as anti-social disorders, schizophrenia and autism. Studying the mechanisms underlying social attachment requires an animal model that displays behaviors similar to that of human social attachment. Prairie voles (Microtus ochrogaster) have become an important model for the study of the neurobiology of social attachment. In the field, male and female prairie voles form long-term, monogamous bonds and share a nest throughout the breeding season. Such a breeding pair typically remains together until one animal dies. Given that mating in prairie voles induces neuroadaptations that eventually lead to bonding, we propose here to investigate whether mating induced social bonding has an underlying epigenetic basis. Our preliminary data support this hypothesis.

Project Summary/Abstract Psychological stress can induce activation of the hypothalamic-pituitary-adrenal (HPA) axis, impairing the function of multiple biological systems and posing a risk to mental and physical health. In contrast, positive social interactions, especially social support from deeply rooted social bonds, can ameliorate stress-induced mental, physiological, and behavioral deficits and improve an individual's overall well-being?a phenomenon known as social buffering [1, 2]. Such social buffering effects have been described in both human [3-5] and animal models [6, 7]. Although we have begun to understand the neuromechanisms underlying biobehavioral responses to psychological stress, little is known about the neuromechanisms by which social support buffers the stress response [1]. This is largely due to the difficulties inherent in studying neurobiological mechanisms in humans as well as a lack of appropriate animal models to assess the effects of social buffering. Recently, the socially monogamous prairie vole (Microtus ochrogaster) has emerged as an animal model to study the neurobiology of social behavior. In prairie voles, mating induces pair bonding, which is regulated by several neurochemicals including oxytocin (OT), vasopressin (AVP), corticotrophin releasing hormone (CRH), and gamma-aminobutyric acid (GABA) [8, 9]. Pair bonding reduces stress-induced anxiety-like behavior by attenuating the action of the HPA axis [10]. Interactions with the partner also promote the release of central OT [11], which plays a role in attenuating the biobehavioral response to stress in female voles [12]. Using this unique animal model, we propose, in Specific Aim 1, to examine how social buffering by a sibling cage mate or a bonding partner attenuates immobilization (IMO)-induced stress responses in male and female prairie voles. We will examine the effects of social buffering on (1) anxiety-like, depression-like, and affiliative behaviors, (2) circulating levels of corticosterone (CORT), (3) CRH, OT, AVP, GABA, and their receptors gene and protein expression in the paraventricular nucleus of the hypothalamus (PVN), and (4) neurochemical release in the PVN during IMO and social buffering. In Specific Aim 2, we will perform pharmacological manipulations with behavioral testing to examine the functional role of PVN OT, and its interactions with GABA, CRH and AVP, in the social buffering of the stress response. In Specific Aim 3, we will examine the neurochemical and physiological involvement of PVN neuromicrocircuitry in the regulation of social buffering. Data from this study will not only enhance our understanding of sex differences in the neurochemical regulation of social buffering of stress responses but also further establish a much needed animal model for such investigation.

PROJECT SUMMARY/ABSTRACT Although it is well known that paternal behavior may be of equal importance as maternal behavior for the physical and psychological well-being of adult partners and their children, our knowledge about the neurobiology of parental behavior is almost exclusively derived from studies of maternal behavior. The scarcity of knowledge on the neurobiology of paternal behavior is primarily due to a lack of appropriate animal models. In recent years, the socially monogamous prairie vole (Microtus ochrogaster) has emerged as a useful animal model for the study of complex social behaviors, including pair bonding between adults and bi-parental care towards offspring [1]. A critical aspect of all behaviors is the epigenetic underpinnings that may influence them. Environmental factors, including social interactions, have profound effects on one?s physiological and behavioral functions. A growing body of evidence has indicated that epigenetic mechanisms can encode these environmental factors in the brain and shape behavior. Social interactions, such as maternal [2], sexual [3], and social defeat [4] experience can affect animal behavior via epigenetic regulations. In prairie voles, treatment with histone deacetylase (HDAC) inhibitors, trichostatin A (TSA) or sodium butyrate (SB), or mating increased oxytocin receptor (oxtr) and vasopressin V1a receptor (avpr1a) gene expression in the nucleus accumbens (NAcc), which occurred through histone acetylation at the oxtr and avpr1a promoters and facilitated social bonding [5, 6]. These data demonstrate the utility of the prairie vole as a model to study epigenetic regulation of social behaviors. In this application, we propose to use male prairie voles as an animal model to test the hypothesis that the HDAC inhibitors facilitate epigenetic regulation of paternal behavior by enhancing neurochemical receptor expression. We will compare male voles that receive intracerebroventricular (icv) injections of vehicle (cerebrospinal fluid: CSF) containing different concentrations of HDAC inhibitors, TSA or SB, in order to reveal the effective dose of the HDAC inhibitors that may enhance paternal behavior. We will then measure global acetylated and unmodified histones, neurochemical receptors (including oxytocin, dopamine, and vasopressin), and TSA- or SB-enhanced histone acetylation at the promoter regions of these receptors in select brain areas important for social behaviors. These data will illustrate the specific gene(s) in brain area(s) whose transcription is enhanced by HDAC inhibitors. Thereafter, we will administer TSA or SB into the brain region, with or without the receptor antagonist, to examine its effect on paternal behavior. Together, these data will shed light on the neurochemicals and brain circuitry important for the epigenetic regulation of male parental behavior ? a scientific question with high translational value for human health.