Regional differences in the development of luteinizing hormone-releasing hormone nerve endings in the rat

The maturing process of LHRH nerve endings in the developing rat brain was systematically studied by immunohistochemistry. LHRH was first detected in the organum vasculosum of the lamina terminalis (OVLT) at the 19th day of gestation, thereafter increasing in amount until it reached the adult level 2 weeks after birth. This increment was accompanied by certain morphological changes, particularly notable was an increase of vascular invasion. LHRH in the median eminence (ME) was detected in only one fetus on the 21st day of gestation and was still not prominent on the 1st neonatal day. From the 2nd neonatal day onward, LHRH was observed in the ME of all animals in the area above the tuberoinfundibular sulcus, from which it extended during the next 2 weeks to the superior labium of the infundibulum at the caudal part of the ME. The gradual accumulation of LHRH continued towards puberty accompanied by growth of the infundibular process without alteration of the immunohistochemical pattern. This differential development of LHRH in the OVLT and ME may indicate the existence of different neuropathways of LHRH and, furthermore, different roles for LHRH in the OVLT and ME.