ACETAZOLAMIDE SPECIFICALLY INHIBITS LINGUAL TRIGEMINAL NERVE RESPONSES TO CARBON-DIOXIDE

The goal of this study was to examine the role of the enzyme, carbonic anhydrase, in oral trigeminal chemoreception with particular regard t o the reception of CO2. Using both single and multiunit recordings of trigeminal neurons in the lingual nerve of rat, we measured responses to cool (24-degrees-C), noxiously hot (55-degrees-C) and cold (8-degre es-C) H2O, NH4Cl and supersaturated solutions of CO2 (24-degrees-C and 33-degrees-C). The importance of peripheral carbonic anhydrase was te sted by inhibiting enzyme activity with acetazolamide (15 mg/kg b.w.). Single unit responses to CO2 and HCl suggest that neural sensitivity to CO2 is not simply a function of extraepithelial pH. Responses to CO 2 were significantly inhibited by acetazolamide while the responses to thermal stimuli and NH4Cl were not. The results support a role for ca rbonic anhydrase in trigeminal responses to CO2. Furthermore, the resu lts suggest that intraepithelial acidification mediated by carbonic an hydrase may be the basis for sensitivity to CO2.