GnRH neurons and other cell populations migrating from the olfactory neuroepithelium.

Cell migration from the olfactory neuroepithelium to the brain has been widely studied during vertebrate development. Immunocytochemical analysis has revealed that many of the migrating cells contain GnRH (Gonadotropin-Releasing Hormone). The GnRH positive cells migrate from the medial olfactory placode, steam along the nasal septum, cross the basal forebrain and reach the hypothalamic and septal areas from where they control the release of hypophyseal gonadotropic peptides. A peculiar feature of these cells is that they start expressing GnRH during migration. 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 double immunolabelling on mouse embryos and on early neonatal Brazilian opossum (Monodelphis domestica) tissues. Beside the GnRH neurones we observed other migrating cells along the pathway traced by olfactory terminal and vomeronasal nerves. Most of these cells co-express carnosine and OMP. The carnosine/OMP migrating cells are detectable in later developmental stages than GnRH neurones. GnRH neurones do not express either OMP or carnosine. By keeping in culture explants of the brain together with the olfactory region from newborn opossums, we have shown that it is possible to obtain the migration of the different populations in vitro. Moreover the GnRH cells are co-distributed, but different from those expressing olfactory markers.(ABSTRACT TRUNCATED AT 250 WORDS)