Rat trigeminal, olfactory and taste responses after capsaicin desensitization.

Experiment 1 showed that capsaicin injections severely reduced or eliminated nasal trigeminal responses to 3 odorants. Experiments 2 and 3 investigated whether desensitized animals could behaviorally detect and discriminate odors. Capsaicin treated animals had no measurable deficits in locating buried food, in odor aversion learning, or in operant odor detection and discrimination. Experiment 4 examined whether behavioral responsiveness to salty, sour and bitter tastes was affected by desensitization. Capsaicin injections did not affect responsiveness to salty or sour, but may have raised rejection thresholds for bitter. Broadly, the present results suggest that substance P-containing fibers mediate trigeminal responsiveness to odorants and irritants but that the loss of this responsiveness does not appreciably affect smell or taste, per se.