Matthew Grober - US grants

9309555 Grober Gonadotropin-releasing hormone (GnRH) is a decapeptide that was isolated from brain in 1971 and has now been shown to exist in at least five different multiple forms. Further, with the development of sophisticated antibody technology, the GnRH neuronal network was demonstrated to be a complex, heterogenous system, comprising three or more distinct neuronal groups and spanning vastly different regions of the brain. While it is known that GnRH is involved in the control of reproductive behavior and physiology in all vertebrates, specific functions for the different GnRH peptides within the different brain regions have yet to be identified. Dr. Grober will examine a vertebrate that exhibits exceptional levels of sexual plasticity as his model system, thus providing an excellent opportunity to investigate how social interactions can trigger profound behavioral and physiological changes via the endocrine system. He will combine molecular, cellular and field endocrinological techniques to determine the role of GnRH in sexual plasticity. Dr. Grober will examine the relationship between GnRH gene expression and changes in physiology and behavior. He will show where and how much GnRH is formed and under what conditions. This integrative approach coupled with an unique model system will provide important insights into the role that GnRH plays in basic mechanisms underlying reproductive maturation, physiology and behavior. ***

PI: Grober, M. IBN-9723817 The long term goal of this research is to understand social regulation of reproductive function. In the bluehead wrasse, social interactions regulate the expression of a wide range of reproductive options, specifically the transformation of both females and males into a 'supermale' reproductive morph; i.e., gender change. This unique fish provides a model system for understanding social regulation of reproductive neuroendocrinology for several reasons: 1) the precise timing of reproductive transitions can be experimentally controlled, 2) behavioral changes occur within minutes of the social trigger and total gender reversal can be completed in eight days, 3) gender transitions result in permanent changes in reproductive behavior, and 4) these differences in behavior result from and/or cause permanent changes in the brain and endocrine system. To approach our long term goal, one central hypothesis will be addressed: Changes in social status induce changes in forebrain Arginine Vasotocin (AVT) centers and gonadal hormone levels, which in turn generate changes in the social and reproductive behaviors that are a necessary component of gender change. This project will focus on AVT because brain centers that produce this peptide hormone exhibit several key characteristics: 1) in many vertebrate species, males and females show dramatic differences in these cells, 2) these cells are sensitive to social modulation and gonadal hormone levels, 3) this peptide regulates social and mating behavior in association with levels of specific gonadal hormones, and 4) these cells undergo rapid and directional changes during gender reversals in the bluehead wrasse. This proposal addresses four specific aims: 1. The precise timing of changes in gender-specific behavior must be determined. 2. These results will be used as a timeline for examining the timing relationship between changes in behavior and changes in the brain cells during gender change. 3. Determination of changes in gonadal hormones that accompany gender change before, during and after gender change. 4. Determination of the affects of gonadal hormones on forebrain AVT cells. Recent changes in average testosterone levels in men and infertility in women are associated with changes in our own social associations. A general understanding of these processes may be gained from the investigation of the social control of reproduction in a range of vertebrates; the bluehead wrasse is a good model system for such studies. This work will provide a detailed picture of how social interactions regulate reproductive behavior, neurobiology and endocrinology. As an RUI proposal, this project will foster the participation of undergraduates in an integrative research program. Students will learn to critically read scientific literature, generate hypotheses and methods for testing these hypotheses, predict possible outcomes, and analyze / discuss their results. In addition, students will get experience with state-of-the-art technologies in biological sciences increasing the range of future opportunities for these students, and their ability to succeed in these fields. Our program caters to undergraduates with non-traditional backgrounds and the goal of this project is to make these students competitive for openings in top quality graduate and professional programs.

Dramatic differences between the sexes are normally established early in development and remain fixed for life. However, in many fishes, reproductive function shows life-long plasticity, with sexual transitions occurring in response to varying social and life history conditions. By manipulating social group composition in bluebanded gobies (Lythrypnus dalli), one can predictably induce the establishment of dominance and subsequent sex change in a targeted female. This female exhibits a stereotyped sequence of behavioral, physiological and anatomical changes as she transforms into a male. One can use early behavioral indicators of dominance to examine the mechanisms that drive both increased social status and the initiation of sex change. Sex steroids have been implicated in the regulation of both of these processes, but gonadal production of sex steroids does not change in the early stages of sex change. However the vertebrate brain synthesizes sex steroids and these enzymatic processes can be down-regulated in minutes. The current project critically examines the relationship between changing social status, rapid regulation of neurosteroid pathways, and the initiation of sex change. Through the determination of brain steroid levels, the rates of enzymatic conversion of one steroid to another and observations of how the animals are behaving, one can determine the dynamic interactions between social and endocrine signals in regulating adult sex change. The evolution and development of sex differences is an area of fundamental importance for biologists and the results of this work will enhance our understanding of how social processes regulate reproductive behavior, anatomy and physiology. The resources of the Education directorate at the Center for Behavioral Neuroscience will be used to recruit women and minorities into the undergraduate and graduate training opportunities available through this grant and the PI has an outstanding record of mentoring women and minorities in scientific research.

What effects do steroids like androgens have on the behavior and reproductive success of organisms? Traditionally, gonads are assumed to be the source of circulating androgens, thereby regulating behavior. Often, however, behavioral changes in response to the environment can be rapid and thus precede changes in circulating androgens. This raises the question as to whether brain-derived androgens are important in regulating behavior.

A particularly fascinating phenomenon is seen in Bluebanded Gobies (Lythrypnus dalli), coral-dwelling fish that inhabit waters off the coast of Santa Catalina Island. These fish exhibit a haremic social structure, in which one large male dominates a group of females. If the male leaves the group, the most dominant female dramatically increases her aggressive and territorial behavior, and transforms into the male. The male provides paternal care by fanning eggs and defending them against predators. This research will address the role of brain androgens in regulating two life-history stages: reproductive transformation and male parenting.

Advanced resources will facilitate an integrative, organism-level approach, including biochemistry, androgen implants, brain pharmacological injections, and hormone measurements, all used within the context of in-depth behavioral observations of wild-caught fish in a semi-natural laboratory setting. Findings are expected to reveal that the brain (rather than gonads) is the predominant source of elevated androgens for the regulation of stereotyped behavioral patterns during life-history transitions.

The results of these experiments will lay a foundation for understanding social behavior as well as cellular and molecular mechanisms driven by steroids. This work will involve the participation of undergraduate minority students who will learn valuable lab techniques and critical thinking skills. Through education outreach activities, findings of this research will be shared in association with the Center for Behavioral Neuroscience, Wrigley Institute for Environmental Studies and the Georgia Aquarium.

Social behavior is a critical target for natural selection because expressing behaviors appropriate for a given social context affects reproduction, resource acquisition, and survival. Social context can vary greatly over a lifetime, however, and it remains unknown how well, and by what means, individuals can deal with this variation. The bluebanded goby (Lythrypnus dalli), a highly social fish, is a useful model for investigating context-specific social interactions because behavior and reproduction are simple to measure, and social context is easy to alter in relevant ways. Hormones such as androgens, which are important for vertebrate social behavior, reproduction, and context-specificity, can also be measured and manipulated in L. dalli. For each status class in a hierarchy of gobies, there are specific social behaviors that promote group reproduction. This work will test for the first time whether those successful individuals can translate prior success into positive outcomes in different social contexts and whether the strategic expression of distinct behavioral patterns underlies that success. The reproductive success of individual L. dalli may be directly regulated by androgens and/or regulation could be indirect via androgen effects on important social behaviors. Androgens acting in the brain may be particularly important for the regulation of L. dalli behaviors associated with reproduction. This work could elucidate an evolutionarily conserved interaction between androgens and reproductive success. Social behavior is complex, and this research approach, which integrates an evolutionary perspective with mechanistic regulation by hormones, will be critical to understanding why and how individuals behave the way that they do. Diverse undergraduates, including women and minorities underrepresented in science, have been, and will continue to be, involved in all stages of this research. This work has already been shared with the public at K-12 schools, museums, and research centers, and these education efforts will continue to be a priority.