John Meitzen

Social play in children and juvenile animals is a highly rewarding behavior and important for social skill development. Social play deficits are seen in children with autism spectrum disorder (ASD) and contribute to their lifelong social dysfunction. This urges the need to understand the neural mechanisms of social play. ASD is 4x more prevalent in males than in females, suggesting sex differences in its neural underpinnings. Furthermore, ASD is associated with abnormalities in the oxytocin (OXT) system and in the brain reward system. Moreover, OXT is a potential drug target to treat social dysfunction in ASD. Yet, virtually nothing is known about the role of OXT in social play. Understanding how OXT regulates social play is expected to inform sex-specific therapeutic strate-gies to improve social function in ASD children. The long-term goal of this research is to identify the neural circuitry by which OXT regulates social play in both sexes. The overall hypothesis is that hypothalamic OXT acts on the brain reward system to regulate social play behavior in sex-specific ways. Our preliminary data in juvenile male and female rats suggest the potential of supraoptic nucleus (SON)-derived OXT to regulate social play by modulating the activity of OXT receptor (OXTR)-expressing neurons in the nucleus accumbens (NAc) that project to neurons in the ventral pallidum (VP). Specifically, we found that (1) the number of activated SONOXT neurons correlated positively with social play duration, (2) pharmacologically antagonizing OXTR in the NAc reduced social play, (3) pharmacological in-hibition of the VP reduced social play, (4) males have twice as many activated SONOXT neurons, (5) males re-quire a higher dose of the OXTR antagonist in the NAc to reduce social play, and (6) males show a different cel-lular phenotype of NAcOTR neurons. Thus, we will test the specific hypothesis that the SONOXT ������������������� NAcOTR ������������������� VP pathway is integral for the sex-specific regulation of social play.

Sex differences in striatal-mediated cognitive and sensorimotor behaviors have been demonstrated for decades. These behaviors and the function of the striatum itself are sensitive to the action of the steroid sex hormone 17��������-estradiol (estradiol) in females but not males. Likewise, many disorders linked to the striatum are sensitive to estradiol action and/or show a sex bias in incidence and/or severity. Remarkably, the mechanisms and extent to which estradiol organizes and then modulates the striatal neuron electrophysiological properties that ultimately enable these changes in function and behavior are not well understood, providing the rationale for this proposal. The overall goal of this proposal is to fill this critical knowledge gap, working towards our long-term goal of understanding how striatal intrinsic and synaptic electrophysiology can be modulated by steroid sex hormones and genetic sex to generate sex differences in function and pathologies. To do this we will focus on the predominant and output neurons of the striatum: the medium spiny neurons (MSNs), and use rats as a model system. MSN action potentials constitute the output of striatal processing. Thus all striatal sex differences must ultimately influence MSN electrical properties to influence behavior. One key electrical property is intrinsic membrane excitability, which governs the ability of a neuron to produce action potentials in response to electrical and synaptic input. We recently discovered that MSN excitability is increased in prepubertal females compared to males, and that excitability is rapidly modulated by estradiol. Increased female MSN excitability was not blocked by glutamatergic and GABAergic receptor antagonists, meaning that increased excitability in female MSNs is not mediated by classical fast neurotransmission. Likewise, no sex differences were detected in excitatory synaptic input. Since sex differences in MSN excitability occur pre-puberty, this raises the exciting possibility that this is organized before adulthood, is re-programmed during puberty, and acutely modulated by adult estradiol action. The central hypothesis of this project, which is based upon these initial findings, is this: estradiol organizes and then acutely regulates MSN excitability via sex specific mechanisms. We will test this hypothesis over the following three specific aims: 1) Elucidate the mechanism underlying organizational actions of estradiol on MSN excitability; 2) Delineate the mechanism underlying rapid actions of estradiol on MSN excitability; and 3) Determine the functional impact of estradiol actions on the excitability of specific MSN subtypes. These studies will have an important positive impact because they will address the neural electrophysiological mechanisms underlying estradiol action in striatal function. This will be an important advancement in fundamental knowledge that is potentially useful for understanding the mechanisms underlying sex differences in striatal pathologies and generating new targets for sex-specific therapies. More broadly, this research will help lead to a better understanding of the relationship between estradiol, genetic sex, and neuron electrophysiological properties.

The Spring Neuroscience Conference consists of talks from North Carolina investigators, a keynote address by Dr. David Anderson from California Institute of Technology, talks from scientists from NC State University, NIEHS and Wake Forest, and a poster session highlighting the research of young scientists. The target audience is investigators and student trainees from North Carolina universities, government institutions and biotechnology companies.

Stem cells are the basic units of developing tissues, and they are employed in regenerative medicine, cellular reprogramming, and cancer biology. Mechanisms of how stem cells communicate with themselves and their offspring is important for basic and applied studies, but are not well understood. An emerging question is how ���������������clonally������������������ related offspring (cells derived from division of a common ���������������mother������������������ stem cell) speak to each other and their mother stem cell, and how this communication dictates their fate. We have established cutting-edge genetic, imaging, and electrophysiological technologies to track the number, fate, and mode of communication among clonal cells in vivo, using the developing brain as a model. Our focus is on a critical period when neuronal production (neurogenesis) switches to production of glia (gliogenesis), a transition vital for normal brain development. Our results are revealing exciting novel concepts in stem cell biology. We propose to mathematically model complex datasets to uncover underlying rules and principles that govern clonal stem cell behaviors. Data obtained from proposed experiments will be used for an application to NIH.

This FRPG is dedicated to generating pilot data for external grant applications. The scientific topic is elucidating the mechanisms by which estradiol organizes female neuron excitability. This question is of key importance given how little is known about how estradiol and genetic sex interact to generate the known estradiol-sensitive and sex differences in striatal-mediated cognitive and sensorimotor behaviors, and relevant pathologies.

How the intrinsic electrophysiological properties of a neuron interact with synaptic input to generate an action potential is a fundamental question of neurophysiology. The vast majority of basic neurophysiology research is performed in males, leaving a critical hole in scientific knowledge regarding basic neuronal electrophysiological properties in females. This is especially problematic in brain regions that are not directly involved in reproduction, including a crucial nexus of the mammalian brain: the striatum. The striatum (including the caudate/putamen and nucleus accumbens shell and core) shows minimal sex differences in gross anatomy and little expression of nuclear sex steroid receptors. Yet, robust and well documented sex differences occur in striatal-mediated sensorimotor behaviors and pathologies such as drug addiction. To elucidate the cellular mechanisms underlying this phenomenon, our laboratory has determined that (1) intrinsic excitability is elevated in rat female medium spiny neurons (MSNs) in the dorsal striatum, and (2) confirmed that mEPSC frequency is increased in female MSNs in the nucleus accumbens core. The next step in unraveling how these sex differences in MSN electrophysiological properties impact striatal function is testing which MSN subtype exhibits these differences. This is key, as the two MSNs project to different brain regions and play distinct roles in striatal functional output. This question is difficult to address in the rat, but transgenic mice with fluorescently labeled MSN subtypes are now commercially available. Thus, this STIR proposal has two specific objectives: Objective 1: Elucidate which MSN subtype in the caudate/putamen shows sex differences in intrinsic excitability. Objective 2: Elucidate which MSN subtype in the nucleus accumbens core shows sex differences in mEPSC frequency.