Pyriform cortex beta-waves: odor-specific sensitization following repeated olfactory stimulation

The first exposure to the odors of carbon tetrachloride, isopentenyl methyl sulfide, methyl ethyl ketone, 2-propylthietane, salicylaldehyde, toluene, 2,4,5-trimethyl thiazoline, or xylene elicits a weakly developed 20 Hz wave response (beta-waves) in central olfactory structures in the rat. Repeated presentations of these odors produces a gradual enhancement or sensitization of olfactory beta-waves over 5-10 trials given in 1-3 min. The odors of 2-aminoacetophenone and 2-hydroxyacetophenone produce sensitization after an average of 15-17 presentations. The sensitized beta-wave response to the odors of 2-propylthietane and xylene persists for at least 5 days and probably much longer. Sensitization to one odor transfers partially or not at all to other novel odors even though repeated presentation of the new odor also produces sensitization. Since the initial negative response of the olfactory mucosa (presumably due to receptor depolarization) is not enhanced by repeated olfactory stimulation, it is presumed that the altered responsivity is due to synaptic changes in central olfactory structures such as the olfactory bulb or pyriform cortex. Finally, data are presented to show that behavioral antifeedant activity by an odorant does not invariably mean that the odorant has the ability to elicit an olfactory beta-wave response.