RAPID RECOVERY FROM CAPSAICIN DESENSITIZATION DURING RECURRENT STIMULATION

Topical desensitization of the tongue was assessed during multiple bou ts of exposure to capsaicin. In the first experiment subjects rated pe rceived irritation as 30 capsaicin stimuli (33 mu M) were applied to t he tongue tip in three blocks of 10, with 15 min breaks between blocks . Significant desensitization was measured at the beginning of the sec ond and third blocks within each session. However, as stimulation cont inued within those blocks sensations of irritation grew toward undesen sitized levels ('stimulus-induced recovery' (SIR)), Desensitization di d not extend across days. The second experiment employed a 10-fold hig her concentration of capsaicin (330 mu M) to determine if SIR was limi ted to low levels of desensitization. SIR occurred as before within se ssions, and the higher concentration produced desensitization across d ays that also exhibited recovery during the first block of stimuli on days 2 and 3. The third experiment included piperine, zingerone and ci tric acid as stimuli to determine if SIR was specific to capsaicin. Pi perine produced SIR under conditions of both self- and cross-desensiti zation with capsaicin, whereas recovery failed to materialize with zin gerone, Citric acid was not significantly cross-desensitized by capsai cin, so recovery could not be measured, Overall the results demonstrat e that desensitization of the tongue produced by either capsaicin or p iperine can be temporarily reversed if stimulation with either chemica l is resumed for only a few minutes. The implications these findings m ay have for hypotheses about the mechanisms of capsaicin desensitizati on and sensitization as well as for clinical applications of capsaicin as a topical analgesic are discussed.