Structural and chemical guidance cues for the migration of GnRH neurons in the chick embryo

Abstract

Publisher Summary This chapter explains the structural and chemical guidance cues for the migration of gonadotropin-releasing hormone (GnRH) neurons in the chick embryo. A body of evidence indicates that neurons producing GnRH or luteinizing hormone-releasing hormone (LHRH) originate in the olfactory placode and migrate along the terminal and/or vomeronasal nerves or the olfactory nerve into the forebrain. In the chick embryo, the migration of GnRH neurons from the olfactory placode starts at embryonic day (ED) 3.5. After that, GnRH neurons are generated continuously in the olfactory epithelium and migrate into the forebrain along the olfactory nerve by about ED 8. From ED 11 to the day of hatching, the majority of GnRH neurons tends to move into their adult position, whereas GnRH neurons in the olfactory epithelium have disappeared. Experimental studies with dye-labeling or chick-quail chimeric transplantation have provided direct evidence for the actual migration of GnRH neurons from the nose to the brain. The migration of GnRH neurons is a unique example of neuronal migration, in which regional boundaries within the nasal-forebrain axis are crossed. The chapter further explains axon-dependent migration of GnRH neurons in the nasal region—effects of olfactory placodectomy and olfactory nerve transection.