DISTRIBUTION AND MORPHOLOGY OF LUTEINIZING-HORMONE-RELEASING HORMONE NEURONS IN A SPECIES OF WILD ANTELOPE, THE SPRINGBOK (ANTIDORCAS-MARSUPIALIS)

The distribution and morphology of luteinising hormone-releasing hormo ne (LHRH) neurones varies between species. The primary purpose of this study was to characterize the distribution and morphology of the LHRH system in a species of antelope, the springbok. This wild antelope ha s a well-defined social structure in which reproductive activity is co nfined to a few dominant, territorial rams. We also sought to determin e whether social or reproductive status could be accounted for by diff erences in the distribution or morphology of hypothalamic LHRH neurone s. Eleven anoestrous female, nine breeding territorial male (TM) and e ight ''bachelor'' male (BM) springbok were obtained, and their reprodu ctive and body conditions were assessed. By using standard immunocytoc hemical techniques, the LHRH system was visualised in the brains of fo ur animals from each group. Immunoreactive neurones were located in a continuum from the septum to the arcuate nucleus, with the majority at the level of the organum vasculosum of the lamina terminalis. Neither the distribution nor the number of cells differed among the three gro ups. Furthermore, the area of LHRH perikarya was similar in both group s of males, suggesting that reproductive differences between TMs and B Ms lie at another level of the neuroendocrine axis. The anoestrous fem ales had significantly larger neurones than males (TM plus BM). This m ay reflect a sex difference in the LHRH system of this wild antelope. However, an alternative explanation is that the male/female difference is related to the comparatively inactive reproductive neuroendocrine state of the females. (C) 1997 Wiley-Liss, Inc.