ONTOGENIC CHANGES IN ODOR SENSITIVITY, OLFACTORY RECEPTOR AREA AND OLFACTORY RECEPTOR DENSITY IN THE RAT

The changes in area and receptor cell density of olfactory epithelium were examined in 0.5- to > 400-day-old rats. In a parallel study the absolute olfactory detection threshold for ethyl acetate of 50- to > 400-day-old rats was determined. The area of the olfactory epithelium increased throughout the range of ages examined. The density of olfactory receptor neurons (determined from counts of olfactory knobs) showed a rapid increase in the first 20 days, a lesser increase until day 220, and decreased in older (> 400 days) animals. Changes in olfactory sensitivity were related to changes in receptor density with maximal sensitivity occurring at approximately 200 days. Because it is known that the number of mitral cells in the olfactory bulb remains the same at these ages, these results suggest that sensitivity may be closely related to the convergence ratio of primary to secondary neurons in the olfactory system.