Capsaicin and its effects on olfaction and trigeminal chemoreception.

Capsaicin injections severely reduced or eliminated nasal trigeminal responses to 3 odorants (Experiment 1). However, capsaicin treated animals exhibited no deficits in locating buried food, in odor avoidance learning, or in operant odor detection and discrimination (Experiments 2 and 3). In addition, capsaicin desensitization did not affect responsiveness to salty or sour, but may have raised rejection thresholds for bitter (Experiment 4). Finally, while desensitized animals rejected menthol solution, they consumed relatively more than controls, suggesting that capsaicin may have menthol sensitivity. 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.