Localization of gonadotrophin-releasing hormone (GnRH) in the hypothalamus of ovariectomized pony mares by season.

Abstract

Fifteen Pony mares, ovariectomized during the previous summer, were randomly assigned to three seasonal treatment groups, winter, spring and summer (N = 5). At the designated season, the animals were killed and hypothalamic areas were collected and assayed by radioimmunoassay for gonadotrophin-releasing hormone (GnRH) activity. The hypothalamic areas were sectioned into 54 5-mm cubes to determine the sites of GnRH storage. Maximum immunoreactive GnRH activity was located in an oblique pattern extending from the arcuate nucleus-median eminence area to the anterior hypothalamic area dorsally and anteriorly. While total hypothalamic GnRH concentrations were not significantly different among seasons (P greater than 0.05), there was a trend towards increasing concentrations in the summer season. Distribution of GnRH activity was significantly different among seasons (P less than 0.05), the change in distribution occurring in the ventral to dorsal plane, as well as anteriorly to posteriorly.