Odorant exposure increases olfactory sensitivity: olfactory epithelium is implicated.

Exposure-induced shifts in sensitivity to odors may involve peripheral and/or central components of the olfactory system. The ability to disconnect the olfactory epithelium from the bulbs provides a unique opportunity to examine how odorant exposure affects each component. In one experiment, odor thresholds were established for either amyl acetate or androstenone. The mice were then exposed for 10 days to the same test odorant for which a threshold was obtained. After exposure, sensitivity to the odorant increased relative to preexposure levels. The mice then underwent bilateral olfactory nerve transection (BNX). When both groups of mice were tested 45-50 days after recovery from surgery and return of olfactory function, increased sensitivity to the exposed odorant persisted; however, 121-203 days after surgery, sensitivity returned to preexposure levels. Another experiment was similar to the first except that mice were exposed to an odorant, either amyl acetate or androstenone, for 10 days beginning 1 day after BNX or sham surgery. When the mice were tested 45-50 days after surgery, sensitivity to the exposed odorant was increased relative to preexposure levels, whereas sensitivity to the nonexposed odorant remained at preexposure levels. Although further work is needed to determine the precise mechanism(s) underlying shifts in sensitivity to odors, these studies provide additional evidence for peripheral involvement in exposure-induced sensitization to odorants and demonstrate the remarkable capacity of the olfactory system to maintain or even regain sensitivity after injury.