GNRH NEURONS AND OTHER CELL-POPULATIONS MIGRATING FROM THE OLFACTORY NEUROEPITHELIUM

Cell migration from the olfactory neuroepithelium to the brain has bee n widely studied during vertebrate development. Immunocytochemical ana lysis has revealed that many of the migrating cells contain GnRH (Gona dotropin-Releasing Hormone). The GnRH positive cells migrate from the medial olfactory placode, steam along the nasal septum, cross the basa l forebrain and reach the hypothalamic and septal areas from where the y control the release of hypophyseal gonadotropic peptides. A peculiar feature of these cells is that they start expressing GnRH during migr ation. We have analysed the presence of immunoreactivity for peptides typically expressed in olfactory neurones, along the migratory pathway followed by GnRH neurones. We have used polyclonal antibodies raised against carnosine and olfactory marker protein (OMP), and performed do uble immunolabelling on mouse embryos and on early neonatal Brazilian opossum (Monodelphis domestica) tissues. Beside the GnRH neurones we o bserved other migrating cells along the pathway traced by olfactory te rminal and vomeronasal nerves. Most of these cells co-express carnosin e and OMP. The carnosine/OMP migrating cells are detectable in later d evelopmental stages than GnRH neurones. GnRH neurones do not express e ither OMP or carnosine. By keeping in culture explants of the brain to gether with the olfactory region from newborn opossums, we have shown that it is possible to obtain the migration of the different populatio ns in vitro. Moreover the GnRH cells are co-distributed, but different from those expressing olfactory markers.These results show that, duri ng embryonic development in mice and early postnatal stages in the opo ssum, several subsets of cells with different functional commitments m igrate along the nasal septum and the basal aspect of the rostral tele ncephalon, to reach their definitive site in the brain. They provide s upport for the feasibility of an in vitro approach to study the develo pment of the olfactory-prosencephalic regions. (Financial Support from CNR, Accademia Nazionale dei Lincei, M.U.R.S.T, Swiss National Scienc e Foundation).