Immunohistochemical studies on the differential maturation of three types of olfactory organs in the rats

Differential maturation of three types of olfactory organs, the olfactory e pithelium (OE), the vomeronasal organ (VNO) and the septal olfactory organ of Masera (MO), was examined immunohistochemically in embryonic and newborn rats by the use of antiprotein gene product 9.5 (PGP 9.5) serum. These olf actory organs were derived in common from the olfactory placode as neuroepi thelia. In the OE, PGP 9.5-immunopositive olfactory cells first appeared at 13 days of gestation. The OE maturated completely, and showed the same cyt ological features as in the adult at 20 days of gestation. The MO first app eared as a dense mass of PGP 9.5-immunopositive sensory cells on the most v entrocaudal part of the nasal septum at 15 days of gestation and was eviden tly isolated from the OE by the decrease of immunopositive cells in the int ercalated epithelium between the OE and the MO at 20 days of gestation. How ever, even at 7 days after birth, the MO did not complete its development a nd contained sensory cells aggregating in the mass. The VNO was separated f rom the nasal cavity at 13 days of gestation as a tubular structure of a ne uroepithelium including PGP 9.5-immunopositive sensory cells. These cells g radually increased in number in the sensory epithelium of the VNO and exten ded their dendritic processes to the free surface at 7 days after birth. Th ese findings clarified the differential maturation of these olfactory organ s. That is, the OE completes its development before birth, while the MO and VNO after birth.