CAPSAICIN MODIFIES RESPONSES OF RAT CHORDA TYMPANI NERVE-FIBERS TO NACL

Single-fiber preparations of the rat chorda tympani (CT) nerve were us ed to study the mechanism of action of capsaicin on salt-taste transdu ction. Capsaicin selectively suppressed the responses to NaCl of the C T nerve fibers (N-fibers) that are sodium-specific (insensitive or poo rly sensitive to potassium). Among the more broadly responsive, cation -sensitive fibers (E-fibers) there are two subtypes, both of which res ponded to capsaicin but in different ways ('enhanced' type and 'suppre ssed' type). In both N- and E-fibers, 5% ethanol (the vehicle for caps aicin) slightly reduced the response to 100 mM NaCl. The suppressive e ffect of capsaicin on the response of the N-type fibers to 100 mM NaCl was significantly stronger than the effect of 5% ethanol. The suppres sion lasted for at least 20 s after the simultaneous application of 10 0 p.p.m. capsaicin-100 mM NaCl. These results indicate that 100 p.p.m. capsaicin can modify the response of CT fibers to NaCl. The observed effect of capsaicin on gustatory fibers could be the net result of opp osite suppressive and enhancing processes in the taste buds cells and excited intra- or extragemmal trigeminal nerve endings.