SHORT-LASTING EXPOSURE TO ONE ODOR DECREASES GENERAL REACTIVITY IN THE OLFACTORY-BULB OF ADULT RATS

We investigated in adult rats whether a relatively short exposure to a novel odour can lead to changes in reactivity of olfactory bulb princ ipal neurons. Naive rats were exposed to isoamyl acetate for 20 min pe r day either for 6 consecutive days or for a single 20-min exposure. C ontrol group was non-exposed. Under anaesthesia, responsiveness of eac h recorded single mitral/tufted cell was tested towards isoamyl acetat e and four other odours. Results show that the proportion of respondin g cells in the exposed groups decreased drastically when compared to c ontrols. In the two experimental groups recorded 24 h following the la st exposure, mitral/tufted cells show a significant decrease in the nu mber of excitatory responses. In parallel, the number of non-responsiv e cells increased by at least a fourfold factor. This decrease in reac tivity was not selective towards the odour used during the exposure bu t concerned any of the five test-odours presented during recordings. F inally, this lower responsiveness was long lasting as it was still obs erved 10 days after the end of the last exposure. This preliminary stu dy points out the importance of even limited sensory experience in neu ral representation of odours.