EXPRESSION OF GAMMA-AMINOBUTYRIC-ACID AND GONADOTROPIN-RELEASING-HORMONE DURING NEURONAL MIGRATION THROUGH THE OLFACTORY SYSTEM

Neurons containing the decapeptide GnRH originate in the olfactory pla codes and migrate into the central nervous system during fetal develop ment. The neurotransmitter gamma-aminobutyric acid (GABA) has been pro posed as a trophic factor and may also influence neuronal migration. I mmunocytochemical analyses were conducted in fetal rats, mice, and hum ans to identify potential developmental relationships between cells co ntaining GABA, and GnRH neurons. Cells containing GABA were found alon g the nasal portion of the GnRH migration pathway in rats, mice, and h umans during development. A peak number of cells containing immunoreac tive GABA was observed in the nasal compartment of rats at embryonic d ay 15. At this time (E15), a majority of GnRH neurons were clustered i n the region of the cribriform plate. By postnatal day 1, all GnRH neu rons had migrated into the CNS and GABA cells were virtually absent fr om the nasal compartment. Double-label and confocal analyses of GABA a nd GnRH in mice and rats demonstrated that some olfactory GABAergic ne urons coexpress GnRH. This implies that neurons that transiently expre ss GABA originate in olfactory placodes and migrate into the forebrain : Based on the transient dual-label and adjacent relationships between GABA and GnRH containing cells in the nasal compartment, and other da ta showing migrational and trophic roles for GABA in development, we s uggest that GABA may directly influence GnRH neuronal migration and de velopment.