Secretion of the hypothalamic neuropeptide luteinizing hormone releasing hormone is critical to reproduction in all mammals. The neural afferents that modulate the activity of LHRH neurons are not known, although gonadal steroids and the catecholamines, especially norepinephrine, are potent stimulators of LHRH secretion. Activity of LHRH neurons may be modulated by neural systems either by direct innervation of LHRH neurosecretory cells or indirectly through interneurons. Nonetheless, these influences must ultimately reach LHRH neurons to influence synthesis and/or neurosecretion. It is the purpose of these studies to identify and morphologically characterize contacts that are afferent to those LHRH neurons that are critical to ovulation in mammals. First, it is hypothesized that there are groups of LHRH neuronal cell bodies that abruptly change their content of immunoreactive LHRH in relationship to ovulation, while other groups do not; and that these """"""""dynamic"""""""" and """"""""static"""""""" groups of cells are present within the forebrain of mammalian species that are spontaneous (monkeys and rats), induced (ferrets) or seasonal ovulators (bats). Second, it is hypothesized that synaptic input to """"""""dynamic"""""""" but not """"""""static"""""""" groups of LHRH neurons changes in relation to ovulation and/or development. Finally, it is hypothesized that among mammals exhibiting different mechanisms of ovulation, afferent contacts to those LHRH neurons that are critical to ovulation, will be morphologically similar; while afferents to other LHRH neurons, whose function is specifically related to the pattern of ovulation, will differ. Afferent synapses will be examined for their plasticity, and, regardless of the degree of plasticity, for morphological parameters in pre- and post- ovulatory females compared to that in prepuberal females and adult males. These studies will utilize light and electron microscopic immunocytochemistry to study relationships between LHRH neurons themselves, between LHRH neurons and catecholamine neurons and between LHRH neurons and other afferents of unspecified origin.
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