Cheryl Sisk - US grants

The goal of this proposal is to launch an investigative program focused on neural and endocrine factors timing puberty in a male mammal, the ferret. Experiments are designed to develop an animal model of male puberty. As such, the proposed studies represent a novel paradigm for determining the neuroendocrine basis for the onset in testis function, namely, the ontogenetic transformation of a discontinuous pattern of luteinizing hormone (LH) secretion by the neuroendocrine system. The specific aims of my research are to: 1) characterize moment-to-moment fluctuation in blood LH concentrations through puberty and correlate the pattern of LH secretion with two key markers of testis function, steroid hormone secretion and spermatogenesis; 2) define the separate roles played by gonadal steroid hormones and hypothalamic maturation as the neuroendocrine mechanisms underlying the pubertal changes in LH patterns; 3) establish the physiological significance of temporal oscillations in pituitary LH release in shaping the onset of testis function; and 4) localize the hypothalamic structure(s) directing the periodic discharge of LH by the pituitary gland. The proposed studies are novel and important. First, they stand in sharp contrast to past studies which have relied on cross-sectional comparisons of the average concentration of reproductive hormones in groups of animals. Second, these studies are important because current explanations of the neuroendocrine basis of puberty are not performed from the standpoint of shaping target organ function by modulating the amplitude, frequency, and duration of pituitary gonadotropin secretion. Finally, the implications of the proposed studies for clinical investigations are profound because they seek to define the temporal limits of hypothalamic-pituitary signaling which initiate steroidogenesis and spermatogenesis, and the neural structures directing periodic oscillations in the trophic signal supporting the onset of the endocrine and exocrine function of the testis.

male; sex behavior; hormone regulation /control mechanism; neuroendocrine system; testosterone; animal puberty; sex hormones; neuroanatomy; neural information processing; steroid hormone; hypothalamus; retinal bipolar neuron; neuropeptides; median eminence; autoradiography; immunocytochemistry; fluorescent dye /probe;

The research project investigates the cellular basis for developmental shifts in responsiveness to endocrine and behavioral effects of testosterone during puberty in males. The hypotheses to be tested include: 1) whether changes in responsiveness to testosterone are mediated by quantitative changes in nuclear retention of steroid in target neurons or differential intraneuronal steroid metabolism; 2) whether the site of action of testosterone negative feedback on gonadotropin-releasing hormone secretion is at the level of neuronal cell bodies or terminals; and 3) whether endocrine and behavioral effects of testosterone are mediated by separate populations of steroid receptive neurons. The experiments employ steroid autoradiography, tract-tracing, immunocytochemistry, and combinations of these techniques.

This award is being given to support student attendance at the Third Meeting of the Society for Research on Biological Rhythms to be held in May 1992. The three-day meeting will include a plenary lecture, symposia, workshops, slides presentations and poster presentations. Attendance will allow students to interact with senior researchers in the field. This type of interaction is an important aspect of training of young scientists. Knowledge of biological rhythms is critical to understanding diurnal rhythms of hormones and brain transmitters in humans as well as seasonal cyclicity in other animal species.

Proposal Number: IBN-9418641 Principal Investigator: Cheryl Sisk This award is to provide a high-resolution epifluorescence microscope for research neuroendocrinologists at Michigan State University. High-resultion fluorescence microscopy will be used to localize biological molecules to specific subcompartments of individual cells within particular areas of the nervous system. These molecules are tagged with fluorescent markers that show particular colors under ultraviolet light. That way different molecules can be tagged with different colors to determine, for example, if a particular pair of molecules occur together or separately inside specific cells. These scientists will use the microscope for concurrent detection of activity-dependent markers and steroid receptor proteins, for comparisons of enzyme expression patterns in mast cells and glia, and for colocalization of neuropeptides and neurotransmitters in different regions of the brain. Furthermore, this technique can be used to determine how the distribution of these molecules changes when the animal is involved in different behaviors or, for example, is subjected to different photoperiods such as those that occur with the seasons. This microscope will also be equipped with a teaching head so that the scientists can use the microscope for teaching undergraduates these state-of-the-art histological and immunocytochemical techniques.

embryo /fetus toxicology; halobiphenyl /halotriphenyl compound

The primary functions of the nervous system are to sense, interpret, and
integrate external and internal stimuli and to generate appropriate
behavioral responses. The influence of external and internal stimuli on
the nervous system and behavior changes across the life span. In
particular, puberty is a period of development during which significant
neural and physiological changes result in the emergence of adult
behaviors. Maturation of the nervous system during pubertal development
results in different responses to external and internal stimuli in
adulthood. The overall objective of this research is to understand
developmental events during puberty that alter the integration of external
and internal stimuli within behavioral neural circuits.

This project focuses on pubertal maturation of the neural circuit that
mediates male mating behavior in the hamster. The perception of olfactory
cues from a female and the presence of circulating steroid hormones are
both obligatory for mating behavior in this species. These sensory and
hormonal stimuli activate neurons within a well-characterized neural
circuit in the adult, and the neural integration of these external and
internal cues leads to expression of mating behavior. Previous research
has determined that olfactory stimuli and steroid hormones do not impact
the nervous system of juvenile males in the same way, and therefore mating
behavior is not expressed. This project will investigate pubertal change
in the interactions among steroid receptors and neurochemical responses to
olfactory cues. The working hypothesis is that in the adult nervous
system, the cellular basis for the integration of sensory and hormonal
information involves activation of progesterone receptors by
neurotransmitters or neuropeptides released in response to female olfactory
cues. We hypothesize that such sensory/hormonal integration is not
accomplished prior to puberty for two reasons: 1) estrogen does not induce
progesterone receptors in neurons of the hypothalamus of juvenile males;
and 2) female olfactory cues do not elicit the neurotransmitter or
neuropeptide responses needed for activation of the progesterone receptor
in prepubertal males. Experiments are designed to test both aspects of
this hypothesis, which is proposed to account for the inability of juvenile
males to express mating behavior. This project will contribute to our
understanding of the cellular mechanisms underlying pubertal maturation of
the neural integration of sensory and hormonal stimuli required for
expression of adult-typical behaviors.

Epidemiological studies indicate 6that estrogen hormone replacement therapy in postmenopausal women reduces the risk of Alzheimer's Disease. One mechanisms by which estrogen may reduce risk of Alzheimer's Disease is inhibition of beta-amyloid plaque formation and ensuing cell death in hippocampus and cortex, which are among the most severely affected brain regions in Alzheimer's Disease. Using cDNA array assays to screen for estrogen-regulated genes in a mouse model of menopause, three genes were identified that are both regulated by estrogen in the hippocampus and frontal cortex and are known to be involved in amyloid precursor protein (APP) processing, plaque formation, and apoptosis. These genes encode transthyretin precursor (TTR), presenilin 1 (PS1), and presenilin 2 (PS2). Presenilins promote neural degeneration by cleaving APP into plaque-forming beta-amyloid peptide fragments (Abeta42) and inducing apoptosis. In contrast, TTR impedes plaque formation by sequestering Abeta42. The cDNA array data suggest two novel mechanisms for neural protection by estrogen: 1) inhibition of PS1 and PS2 gene expression, and 2) stimulation of TTR gene expression. The goal of the proposed project is to confirm and extend the findings based on cDNA arrays. The Specific Aims are to 1) confirm and precisely quantify estrogen regulation of TTR, PS1, and PS2 mRNA and protein are regulated by estrogen using in situ hybridization histochemistry and immunocytochemistry. The proposed studies employed a newly developed in vivo mouse model of menopause in which tissue responses to estrogen are assessed and compared when hormone replacement therapy is begin in either early or late menopause. The long-term goal of this work is to contribute to the development of hormone replacement strategies for post-menopausal women that are optimally effective in delaying or preventing the progression of Alzheimer's Disease.

DESCRIPTION (provided by applicant): Multidisciplinary and integrated approaches offer the best hope for understanding the nervous system. The Neuroscience Program at Michigan State University has provided such comprehensive graduate education and research training since 1975. The Program was structurally reorganized in 1998 in order to better meet three training goals: 1) provide students with a solid and integrated foundation in the structure and function of the nervous system from molecules to behavior; 2) provide specialized research training in the fundamentals of scientific methods and current and cutting-edge methodologies to enable students to address fundamental questions in neuroscience; and 3) prepare students for successful independent research and education careers in the public and private sectors by providing instruction in professional skills, scientific ethics, and career development. As part of the reorganization, the Neuroscience Training Program now leads to the Ph.D. in Neuroscience. This Training Program will provide support to predoctoral neuroscience students during the first two years of study, when training is broad-based and before thesis work is begun. Students will interact closely with training faculty via core courses, laboratory research, and special courses designed to enhance scientific and professional skills. A primary strength of the Neuroscience Training Program is the diversity of the training faculty, who come from nine different departments. Their well-funded research programs represent a wide spectrum of disciplinary approaches, including in vivo and in vitro model systems and molecular to behavioral analyses in a variety of vertebrate and invertebrate species. The faculty is interactive and committed to providing the highest quality graduate training in neuroscience. Capitalizing on the diverse faculty and substantial infrastructural resources available at Michigan State University, the Neuroscience Training Program will train integrative neuroscientists who are well-prepared to contribute substantially to the discipline as active researchers and educators.

Animals have internal biological clocks that enable them to coordinate physiological and behavioral rhythms relative to the time of day, termed circadian rhythms. In mammals, a key part of clock in the brain is the supra-chiasmatic nucleus (SCN) of the hypothalamus. In nocturnal rodents, which are widely used in the laboratory, the SCN is known to be important for the timing of female reproductive behavior and a surge in the luteinizing hormone (LH) that triggers ovulation. However very little is known about diurnal rodents, which have evolved from nocturnal species. This project asks how the neural mechanisms responsible for circadian control of the female reproductive cycle have changed in diurnal compared to nocturnal rodents. The model animal is the unstriped Nile grass rat, which is related to common laboratory rats, but has a virtually complete reversal in the timing of a variety of events associated with female reproduction, including morning instead of evening timing for both mating behavior and for the surge in LH. Cytochemical, anatomical and behavioral approaches will be used to distinguish whether the SCN itself changes signal timing, whether there is instead a change in the timing of receptiveness of target sites to SCN signals, or whether there is a change in the neuroanatomy connecting SCN to different targets in nocturnal and diurnal species.
The results will have an impact beyond neuroendocrinology to chronobiology, hypothalamic physiology, and evolutionary physiology. In addition, training of students and researchers at several levels is an important part of the project.

DESCRIPTION (provided by applicant): Adolescence is associated with the emergence of several sex-biased mental illnesses, including eating, mood, and conduct disorders and schizophrenia. Each of these psychopathologies involves impairments in social information processing and social proficiency, which together comprise the ability to recognize, perceive, and interpret socially-relevant information and to apply it appropriately in specific social contexts. A fundamental but unanswered question about normal adolescent development is which of these two aspects of adolescent maturation are governed by pubertal gonadal hormones and which are not, and what neural mechanisms underlie hormone-dependent and -independent remodeling of social behavior circuits. The proposed research uses a well-suited laboratory rodent model, the male Syrian hamster, to empirically test the hypothesis that the adolescent transition in social information processing is gonadal hormone-independent, while adolescent maturation of social proficiency is gonadal hormone-dependent. Using a conditioned place preference paradigm and experimental manipulation of social experience, Aim 1 will test the hypothesis that adolescent changes in social information processing are governed by hormone-independent developmental processes that alter the rewarding properties of social stimuli, whereas adolescent maturation of social proficiency, the ability to make behavioral adaptations in response to social experience, is programmed by testicular hormones during puberty. Aim 2 will characterize neural activation patterns in response to female sensory stimuli, as indexed by fos expression, to determine how neural responses to social stimuli are altered by the presence or absence of testicular hormones during adolescent development. Using the cell birth-date marker bromo-deoxy-uridine in combination with markers of cell function and pharmacological inhibition of brain cytogenesis, Aim 3 will investigate whether the pubertal addition of new cells to social behavior circuits is a mechanism by which gonadal hormones organize the adolescent brain. This research will establish an understanding of hormone-dependent and hormone-independent components of the adolescent maturation of social behaviors, and will investigate a novel mechanism by which gonadal hormones organize and remodel the adolescent brain. The identification of specific aspects of normal adolescent development that are hormone-dependent versus hormone-independent will advance understanding of the role that pubertal hormones play in the etiology of sex-biased mental illnesses associated with adolescence, and will facilitate the development of more effective strategies for prevention and treatment of these disorders.

DESCRIPTION (provided by applicant): Adolescence has only recently been recognized as a protracted period of extensive brain remodeling. This critical period of development is associated with the emergence of sex differences in susceptibility to and manifestation of several mental illnesses, including eating, mood, and conduct disorders, and schizophrenia. Thus, the etiology of these illnesses is likely to be impacted by how pubertal hormones influence the remodeling of sexually differentiated behavioral circuits during adolescence. The longstanding view has been that sexual differentiation of the brain occurs during late embryonic or early postnatal brain development, and that these sex differences are passively maintained throughout adolescence and into adulthood. Recent findings from the PIs'laboratories overturn this view by providing evidence in rats for active maintenance of sexual dimorphisms during puberty via active and hormonally modulated cell addition in sexually differentiated cell groups during puberty. This finding represents a fundamental shift in the understanding of how and when sexual dimorphisms in the brain are established and maintained in the mammalian brain. This newly discovered developmental process may be an active mechanism for either maintaining structural and functional sexual dimorphisms in the face of remodeling of the adolescent brain or for creating new sex differences that emerge during adolescent development. Using timed injections of bromo-deoxyuridine (BrdU) coupled with immunohistochemistry for markers of neurons and glial cells, as well as functional assays, the mechanisms underlying this addition of new cells to the adolescent brain will be determined. The questions to be addressed are: 1) Do gonadal hormones modulate the pubertal addition of cells to the adolescent brain in cell groups that are either male-biased or female-biased by increasing cell proliferation, survival, or both? 2) Is addition of new cells a pubertal or a life-long mechanism for maintenance of structural sexual dimorphisms? 3) What are the fates and functional outcomes of cells that are added to the adolescent brain during puberty? These studies will generate new knowledge and potentially new therapeutic targets to explain and appropriately treat sex-biased mental illnesses that are associated with puberty and adolescence. PUBLIC HEALTH RELEVANCE: Mechanisms of sexually differentiated brain remodeling during adolescence. Adolescence is a critical period of development associated with the emergence of sex differences in susceptibility to, and manifestation of, several mental illnesses, including eating, mood, and conduct disorders, and schizophrenia. We have recently discovered that new cells are added to the adolescent brain, and that hormones produced by the ovaries and testes alter the addition of new cells to different cell groups in the brain, producing sexually differentiated brain circuitry. The goal of these studies is to understand precisely how hormones affect this remodeling of brain circuitry in an effort to shed light on the etiology and progression, and ultimately treatment and prevention, of mental illnesses that emerge during adolescence and affect young men and women differently.

DESCRIPTION (provided by applicant): The mission of the Michigan State University (MSU) Spartan MARC U*STAR program is to address the economic and social imperative to increase the number of talented and well-trained underrepresented minority (URM) students who pursue graduate degrees in the biomedical sciences. The program objectives are to 1) beginning in Year 1, provide access for 20 URMs annually to mentored research opportunities with research active faculty in the biomedical sciences, 2) beginning in the fourth year of the grant, triple the number of URMs pursuing their PhD in the biomedical sciences over the baseline each year, 3) improve the institutional culture at MSU related to URM participation in mentored scientific research and the pursuit of doctoral degrees in biomedical fields, and 4) increase the number of MSU underrepresented undergraduate students who apply for national/international awards (e.g. Goldwater, NSF Graduate Fellowships). The program will consist of 20 pre-MARC Scholars (entering URM students) who will participate in two intensive research-related mathematics courses in the summers prior to their first and second years. During their first two years, the cohort will engage in small group mentored research seminars and participate in a variety of seminars and activities designed to acculturate them to the scientific process and to prepare them for a focused research experience. From this cohort of pre-MARC students, ten MARC Fellows will be selected and will receive stipend and tuition support for their junior and senior years. The core of the MARC Fellows program is a two- year research experience with experienced, dedicated MSU faculty mentors. Faculty mentors will be matched with MARC Fellows based on the strength of their research programs, level of research funding, and their reputation for mentoring undergraduates in their laboratories. The MARC-phase research experience will be augmented by monthly seminars on responsible conduct of research and workshops designed to enhance the Fellows' competitiveness for scholarships, awards, and admission to graduate programs. MARC Fellows will have an extramural research experience at another institution between their junior and senior years and the Fellows will attend the Annual Biomedical Research Conference for Minority Students in both years of the MARC program, presenting their research at this meeting in their senior year. The Program will be assessed by internal and external evaluators. The benchmark for success will be an increased number of MSU URM students entering high quality graduate PhD programs in the biomedical sciences and the impact of the MARC U*STAR Program on the MSU's institutional culture related to URM participation in the biomedical sciences. Because the grant is five years and only two cohorts of students will proceed to graduation in that time, the evaluation of the program will include pre- and post-survey of student knowledge, perceptions and attitudes related to research and pursuit of doctoral studies in the biomedical sciences, monitoring of student progress including academic performance, and presence of URMs in campus-wide undergraduate research initiatives.