CHARACTERIZATION OF HYPOTHALAMIC NEUROPEPTIDES IN MAMMALIAN REPRODUCTION

Understanding of regulation of reproduction at the level of the brain changed dramatically with the discovery of reproductive neuropeptides. To date there have been no studies to characterize the distribution of reproductive neuropeptides in the bovine hypothalamus at different stages of the estrus cycle or to determine the physiological effects of peripheral administration of Gonadotropin inhibiting hormone (GnIH) in intact female cattle and ovariohysterectomized bitches.

The goal of the first study was to determine distribution and connectivity of kisspeptin, dynorphin, and GnIH in the hypothalami of sexually mature female cattle during the estrous cycle. To this end, hypothalami of female cattle were collected during periestrus and diestrus. The neuroanatomical distribution, synaptic connectivity, and response to different circulating progesterone concentrations suggest these neuropeptides play a pivotal role in the regulation of reproduction in cyclic cattle.

Another goal was to test the hypothesis that IV administration of GnIH would decrease serum LH concentrations in post-pubertal heifers. Two studies were carried out to this end. The objective of the first study was to determine whether IV GnIH administration would decrease basal serum LH concentrations. The objective of the second study was to determine whether continuous IV administration of GnIH during the expected time of the LH surge had an effect on serum LH concentrations and ovulation. Results suggest that exogenous administration of GnIH decreases basal LH concentrations but is not able to suppress the surge release of LH or ovulation in post-pubertal heifers.

Finally, the objective of the third study was to determine the effects of IV administration of GnIH on serum LH concentrations in ovariohysterectomized bitches as a potential alternative to surgical sterilization. Results suggest that IV administration of GnIH is not able to suppress serum LH concentrations in the ovariohysterectomized bitch.

In summary, expression of kisspeptin, dynorphin, and GnIH changes with progesterone concentrations in sexually mature female cattle. In addition, exogenous administration of GnIH affects basal plasma concentrations of LH but not LH surge characteristics in sexually mature female cattle. It also appears that exogenous administration of GnIH does not affect plasma LH concentrations in ovariohysterectomized adult bitches.