Douglas L. Foster - US grants

When nourishment is inadequate or energy expenditure is great, fertility is reduced in the adult, and puberty is delayed in the developing individual. This suppression of reproductive activity is not understood mechanistically. We believe this to be an integrative problem at this stage of inquiry that requires both physiologic and pharmacologic approaches to answer broad questions about how the brain discriminates how well nourished and how mature the body is. Our broad objective is to understand the physiological mechanisms by which changes in nutrition and metabolism control reproduction, specifically the signals, sensors, and pathways whereby blood-borne information regulates GnRH secretion. To progress further in understanding the relationship between growth, metabolism and production of high frequency GnRH pulses during development, we must first determine how energy metabolism regulates GnRH secretion. To progress further in understanding the relationship between growth , metabolism and production of high frequency GnRH pulses during development, we must first determine how energy metabolism regulates GnRH secretion in the adult. Thus, we will first evaluate how changes in glucose availability and leptin modify GnRH secretion during adulthood and then determine if such a mechanism might be timing puberty during growth. The sheep will be used because its large size and long lifespan permits individuals to be studied longitudinally through their development and permits detailed studies in adults. Importantly, it is well suited for the characterization of hypophysiotrophic hormone patterns. Specific Aim 1 will determine if the hindbrain and the liver contain sensors that transmit information about glucose availability to regulated GnRH secretion. We will both increase and decrease availability locally in each site to establish their function and their interrelationships. Specific Aim 2 will determine the role of leptin as a signal to regulate the pulsatile secretion of GnRH. This will be achieved through central administration of leptin during both acute fasting and chronic low nutrition. Although widely studied in feeding behavior, we have little understanding of its physiologic role in regulating GnRH secretion. Specific Aim 3 will assess "nutritional stress" as a cause hypogonadotropism through reduced GnRH secretion by monitoring of stress peptides in the pituitary portal circulation and by antagonizing their action during acute fasting and chronic low nutrition. Specific Aim 4 will determine if glucose availability times the pubertal GnRH increase by using the power of our large animal model in which we can chronically administer metabolically important signals such as insulin and leptin. Understanding the metabolic control of GnRH secretion has broad application both to growth and maturation and to other physiologic conditions in which reduced GnRH secretion may contribute to infertility because of altered energy metabolism. These include dietary malnutrition from eating disorders; during high-energy expenditure, as in exercise- induced amenorrhea and lactational anovulation; during type 1-diabetes- induced infertility.

The underlying rationale for this Core facility is that a single, well- designed large animal research facility can effectively and economically meet the needs of several projects. Within the framework of a common physical facility, it is not in the interest of economy and uniform standards of animal care for each user to provide separately for animal husbandry and research needs. Given this rationale, the objective of the Sheep Research Core is to provide a mechanism whereby a common facility with common personnel is shared efficiently by all investigators who wish to use sheep to perform research focused on the reproductive sciences. To this end, the Sheep Research Core will provide a physical facility for maintaining and conducting experiments on sheep, coordinate effective and economical usage of sheep including a uniform high standard of animal maintenance and veterinary care, and perform technical services and offer training.

ABSTRACT IBN 97-28032 PI = THOMPSON, ROBERT C. Regulation of Reproductive and Stress Axes by the Metabolic Signal, Leptin Food availability affects reproductive function. Key to understanding as well as many other bodily functions, lies in our ability to understand how the brain gathers information on the availability of food. A major gap in our understanding of how food availability controls reproduction was filled recently with the discovery of a hormone called leptin. Blood leptin concentrations increase after meals in most animals reporting to the brain a satiety signal. Exactly how the brain senses these satiety signals like leptin is only beginning to be understood. Dr. Thompson will determine how the brain senses leptin and more specifically, communicates this leptin information to brain centers that control reproductive function. One hypothesis tested in this research plan is that information about altered food availability is relayed to the reproductive brain centers via brain centers that are involved in sensing "stress". This idea arose when researches from different backgrounds demonstrated two points. First, stress or stressful experiences have negative effects upon reproductive systems. Second, during conditions where food availability is very low, brain systems known to control stress are activated. Thus, conditions where food is in very short supply are stressful. However, little is known if the activation of these stress systems is the path by which information concerning severely reduced food availability is communicated to reproductive systems. This will be examined in this project. Additionally, many molecules in addition to leptin serve as "food signals". One other signal is glucose. Do different food signals communicate to the reproductive system using the same pathways or are there unique pathways for each food signal? Using similar logic, are all stressful situations or conditions influence d by food signals? Dr. Thompson will explore these questions and information developed in this work will be used to further understand how the brain uses food information to control reproductive function.

The objective of the Sheep Core is to provide a mechanism whereby the services of common personnel are shared by all projects of this Program Project Grant, enabling cost-effective breeding and animal maintenance programs of exceptionally high standards. The underlying rationale for this Core is simple. A staff of well-qualified individuals can meet the needs of multiple research projects more effectively and economically than if each project were to meet its needs separately. This is especially important given that a major function of this core will be to generate sheep that have been programmed prenatally by exposure to gonadal steroids at known stages of pregnancy. This requires extensive experience and expertise of managing fertility, breeding, and early postnatal care in this experimental species. The Specific Aims of the Sheep Core are as follows. Specific Aim 1. To operate a breeding program to generate sheep that are prenatally treated with gonadal steroids at specific fetal ages and vehicle-treated control sheep for use by the three research projects that make up this Program Project Grant. Specific Aim 2. To coordinate effective and economical usage of sheep by three interrelated research projects. Specific Aim 3. To provide a uniform and high standard of animal maintenance and veterinary care. Specific Aim 4. To provide a technical knowledge base for reproductive research in sheep. By achieving these aims, the Sheep Core will greatly enhance the productivity of all projects in the Program Project Grant.

The overall objective is to understand the role of prenatal androgens and estrogens in the programming of feedback systems that control GnRH secretion. Our hypothesis is that exposures to androgens and estrogens before birth decrease the sensitivities of the feedback control of GnRH secretion and that this is facilitated by postnatal exposure to estrogens. The specific aims are to determine: 1) the roles of prenatal androgens and estrogens in programming adult steroid feedback control of GnRH secretion; 2) if prenatal exposure to sex steroids exacerbates the actions of postnatal estrogen to modify steroid feedback control of GnRH secretion; 3) if early exposure to androgens and estrogens programs type, number and distribution of hypothalamic steroid receptors and the type or number of synaptic and glial associations with GnRH neurons. We have extensive experience with unraveling how prenatal exposure to sex steroids alters postnatal sensitivity to steroid negative feedback and the timing of the pubertal rise in GnRH secretion. We will extend our inquiry into postpubertal timing mechanisms that underlie the ovulatory cycle. We will focus on four feedback controls of GnRH. We propose that these feedback controls are inherent in the female and that they are abolished or desensitized by testosterone and its metabolites to result in the single GnRH feedback control system of the male. In the female, selective pathophysiologic programming of these feedback controls early in development by excess testosterone should prevent or disrupt ovarian cyclicity. We will continue our complementary integrative physiological and anatomical investigations. We will create novel neuroendocrine phenotypes experimentally to test hypotheses about the differentiation of the function of, and neuroanatomical organization and activation of GnRH secretion. Our strategy will be to expose the developing female to various steroids and determine their effect on the four major controls of GnRH secretion in the ovulatory cycle. These same well-characterized females will then be used for testing hypotheses about prenatal programming of presynaptic input to GnRH neurons and functionality of GnRH feedback. The results have relevance to our understanding of how the prenatal hormonal environment influences normal and abnormal postnatal activation and function of the reproductive neuroendocrine system. Inappropriate early programming can predictably lead to abnormal onset and maintenance of ovarian cyclicity.