MIGRATION OF LUTEINIZING-HORMONE-RELEASING HORMONE (LHRH) NEURONS IN EARLY HUMAN EMBRYOS

Luteinizing hormone-releasing hormone (LHRH) neurons originate in the epithelium of the medial olfactory pit and migrate from the nose into the forebrain along nerve fibers rich in neural cell adhesion molecule (N-CAM). The present study examined the ontogenesis of LHRH neurons i n early human embryos and found a similar pattern of development of th ese cells. Luteinizing hormone-releasing hormone immunoreactivity was detected in the epithelium of the medial olfactory pit and in cells as sociated with the terminal-vomeronasal nerves at 42 (but not 28-32) da ys of gestation. The migration route of these cells was examined with antibodies to N-CAM and antibodies to polysialic acid (PSA-N-CAM), whi ch is present on N-CAM at certain stages of development. Neural cell a dhesion molecule immunoreactivity was present in a population of cells in the olfactory placode of the earliest embryos examined (28-32 days ) and later (42 and 46 days) throughout the migration route. The PSA-N -CAM immunoreactivity was not detected until 42 days and was present i n a more limited distribution in nerve fibers streaming from the olfac tory placode and along the caudal part of the migration route below th e forebrain. Previous studies have indicated that the highly sialated form of N-CAM: is less adhesive. The PSA-N-CAM may therefore facilitat e the migration of these cells by lessening the adhesion between the f ascicles that make up the migration route, expediting the passage of c ords of LHRH cells between the nerve fibers as these cells move toward the brain. (C) 1996 Wiley-Liss, Inc.