Topographical projection of the septal organ to the main olfactory bulb in rats: ontogenetic study.

Using the horseradish peroxidase (HRP) retrograde tracing method, we have studied the topographical organization of the projection of the septal organ to the main olfactory bulb in rats varying in age from 22 fetal days up to 15 postnatal days. For all developmental stages studied, receptor cells of the septal organ had their axons ending in a relatively circumscribed region of the olfactory bulb, which was the posterior ventromedial bulbar aspect. In younger animals, olfactory receptor cells were observed within the epithelial area isolating the septal organ from the olfactory epithelium, whereas this area was reported to be an exclusive respiratory region in adult rats. The complete disappearance of these receptor cells noted in 12-day-old rats was related to some ontogenetic process.