PRENATAL DIFFERENTIATION OF MOUSE VOMERONASAL NEURONS

The vomeronasal organ (VNO) subserves basic chemosensory functions in rodents, mainly related to sexual behaviour, In order to understand ea rly stages of the VNO structural maturation, we have undertaken an imm unocytochemical analysis of the VNO of fetal mice, Our results demonst rate that Olfactory Marker Protein (OMP), a marker of differentiated c hemosensory cells, is already expressed in vomeronasal neurones and th eir fibres projecting to the accessory olfactory bulb during the last week of gestation, However, in contrast to the adult, where its expres sion is restricted to the medial sensory neuronal component of the VNO , during fetal development OMP is also present in cells located in the lateral non-sensory epithelial component, Some other markers of nasal chemosensory neurones, such as GAP-43/B-50, Protein Gene Product 9.5 (PGP 9.5) and carnosine are also transiently expressed in this ectopic site, These results indicate that (i) significant morphological and b iochemical maturation of the VNO is achieved before birth; (ii) transi ent cell populations, sharing the biochemical profile of the vomeronas al chemosensory receptors, occur in ectopic areas during fetal develop ment.