Ontogenesis of the axonal circuitry associated with the olfactory system of the rat embryo.

The prenatal development of axonal connections in the rat olfactory system was studied using DiI. On day 16 (E16), the olfactory and vomeronasal nerves extended from the olfactory epithelia to the olfactory bulb (OB), the terminal nerve to the telencephalic septum, while axons of mitral and tufted cells reached the anterior olfactory nucleus (AO). Axons from the AO were also seen in the anterior commissure. On day E16(8) (at 16 days, 8 h), axons were anterogradely followed from the dorsal OB through the lateral olfactory tract (lo) to the bed nucleus of the accessory olfactory tract. At E18(0), crystals implanted in the olfactory epithelium labeled the mitral cell layer and the lo.