Neuroendocrine mechanism of estrous behavior in the Shiba goat

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Onset of estrous behavior is under the endocrine control in mammalian species. Development of preovulatory follicles is accompanied by increasing estradiol secretion, and the rise of circulating estradiol level induces the estrous behavior as well as the preovulatory LH surge in most species, despite considerable inter-species differences of actual behavioral pattern of estrus. The central neuronal mechanism eliciting both the estrous and the LH surge is, however, poorly understood.In the present study we studied about the gonadotropin-releasing hormone(GNRH)neuron in the Shiba goat from various aspects using electrophysiological, immunohistochemical and biochemical techniques. The hypothalamic decapeptide GNRH is not only regulating the pituitary gonadotropin secretion but also known to be involved in the expression of estrous behavior. The study consists of following four main subjects.[1]Developmentof the method for stereotaxic surgery of the goat brain.[2]Electrophysiological inves … More tigation of the GNRH pulse generator activity.[3]Immunohistochemical localization of GNRH neurons in the brain.[4]Microdialytic analysis of GNRH neurosecretion at the median eminence.By adopting the latest neurophysiological techniques we were able to monitor the neurosecretory activity of hypothalamic GNRH neurons in conscious and unrestrained goats. Major finding are as follows : (1)Majority of GNRH immunoreactive cells are distributed in the preoptic/septal area and project their fires caudally to the median eminence via two main pathways, (2)the GNRH pulse generator activity, as assessed by hypothalamic MUA volleys, continues with decreased pulse frequency during the LH surge induced by estradiol in ovariectomized goat, (3)GNRH levels in the microdialysis perfusate increase dramatically at the onset of LH surge. These results, taken together, suggest that the LH surge that is normally associated with the estrous is induced by the GNRH surge, and this Gn* surge is under the control of a neuronal mechanism that is intrinsically different from the GNRH pulse generator that regulates basal patterns of gonadotropin secretion. Less