ODORANT THRESHOLD FOLLOWING METHYL BROMIDE-INDUCED LESIONS OF THE OLFACTORY EPITHELIUM

The present study assessed the functional consequences of peripheral o lfactory destruction on the minimum detectable levels of stimulation f or the odorants 2-propanol, D-limonene, and ethyl acetoacetate. Using standard operant techniques, eight Long-Evans rats were trained to cri terion on an air versus odor differential response task. Odorant thres hold was then determined on 10 consecutive testing sessions, using a c omputer-automated olfactometer and psychophysical tracking procedure. Following the last testing session, the rats were lesioned by exposing them to 330 ppm methyl bromide gas for 6 h. For each lesioned animal the anatomical state of the olfactory epithelium was evaluated relativ e to behavioral performance on the odorant threshold task at 3 days po stlesion. For the group of rats, a comparison of pre-and postlesion pe rformance demonstrated that, on the average, odor sensitivity was not altered by lesions that destroy roughly 95-98% of the epithelium. Howe ver, analysis of individual cases illustrated that two of the eight ra ts showed an elevation in odor sensitivity, albeit minimally, that was considered different from the prelesion performance. For those animal s affected, we could extract no apparent relationship between the beha vioral findings and the extent of anatomical damage. The results of th is study demonstrate the remarkable capacity of the olfactory system t o maintain normal or near-normal detection sensitivity in the face of massive damage. This capacity presumably reflects both the normal expo sure of the epithelium to continual injury and the importance of maint ained olfactory function for the survival of the animal. (C) 1997 Else vier Science Inc.