Restoration of olfactory mediated behavior after olfactory bulb deafferentation

Transection of olfactory nerve fibers leads to deafferentation of olfactory bulbs and a loss of olfactory mediated behavior. Nerve transection studies have shown that during recovery, olfactory nerve fibers can reestablish connections with the olfactory bulbs. Two groups of experimental animals were studied to determine if olfactory mediated behavior returns after recovery. One group (n = 18) received bilateral olfactory nerve transection (BTX), while the second group (n = 4) received a sham surgical procedure. Performance on odor detection and discrimination tasks was measured during recovery periods ranging from 1–120 days. Return of olfactory mediated behavior was first observed 19 days after nerve transection. Performance levels improved with recovery time and by day 40 animals returned to criterion level (≥ 90% correct response). Sham animals maintained a criterion level of performance throughout the recovery period. Horseradish peroxidase (HRP) was used to trace reconnection of olfactory nerve fibers. The absence of HRP label in the bulbs of animals examined one day after BTX, verified the completeness of the nerve transection procedure. After 10 days of recovery, a few HRP labeled axons were observed and the amount of HRP in the bulb increased with recovery time. The results of this study demonstrate that olfactory receptor axons can reestablish functional connections with the deafferented olfactory bulb and these connections are sufficient to restore olfactory mediated behavior.