Project II - Steroidal and Metabolic Mediation of Neuroendocrine Circuitry

University Of Michigan At Ann Arbor, Ann Arbor MI

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Abstract

Prenatal T excess results in reproductive and metabolic neuroendocrine deficits manifested at a hypothalamic level, as well as deficits in ovarian and behavioral function. The hyperinsulinemia and/or hyperandrogenism that occur as a consequence of prenatal T exposure are detrimental to reproductive neuroendocrine function. Changes in the latter most likely reflect alterations in the feedback control of GnRH secretion, which is conveyed by specific neural circuitry to the GnRH neuron, the latter of whose projections to the median eminence comprise the final common pathway controlling mammalian reproduction. We have identified a key group of neurons that co-express dynorphin, neurokinin B and kisspeptin in the arcuate nucleus of the hypothalamus, and which play a critical role in the feedback control of GnRH secretion in the sheep. Prenatal T exposure results in a decrease in gonadal steroid receptors in these cells and an imbalance of inhibitory (dynorphin) and stimulatory (kisspeptin) neuropeptides - we hypothesize that 1) T acts directly via androgen receptors and/or indirectly by altering insulin homeostasis to induce these alterations, and that 2) these changes lead to an inability of this subpopulation to convey the influence of gonadal steroids, including the inhibitory influence of progesterone, to GnRH neurons. Aims 1 and 2 will explore these two possible mechanisms of T action, and Aim 3 will directly test the second hypothesis using pharmacological or genetic interventions to normalize the balance of neuropeptide expression in this neuronal subpopulation. In addition, in Aim 3 we will determine whether prenatal T causes epigenetic modifications in neuropeptide and/or receptor genes expressed in the ovine arcuate nucleus. Finally, we have found that prenatal T treatment leads to an increase in AgRP peptide expression, a key appetite regulatory peptide involved in metabolic homeostasis. Aim 4 will expand these preliminary observations to other appetite regulatory systems and determine the mechanisms ofT action on these systems.