Embryonic and postnatal differentiation of olfactory epithelium and vomeronasal organ in the Syrian hamster

The details of the embryonic and postnatal differentiation of the olfactory epithelium (OE) and vomeronasal organ (VNO) were examined by light and electron microscopy in the Syrian hamster. At 10 days of gestation, the nasal placode is invaginated to form the olfactory pit on either side at the rostral end of the embryo. Abundant mitotic figures are observed near the free surface of the epithelium lining the olfactory pit. At 11 days of gestation, the mass of the epithelium lining a recess is separated from the medial wall of the olfactory pit to form the VNO. At 13 days of gestation, mitotic figures become observable in the basal layer of the vomeronasal sensory epithelium (VSE) in addition to the superficial to middle layers, while in the OE mitotic figures are observed mainly in the middle to basal layer. At 1 day after birth, the OE is almost complete in differentiation. On the other hand, the VSE differentiate slowly to retain some immature properties even at 10 days after birth. These findings suggest that the olfactory function seems to be solely ascribed to the OE for a while after birth. The significance of mitotic figures are discussed in the course of development with special reference to the origin of the nasal placode from the central nervous system.