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 to 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°C), noxiously hot (55°C) and cold (8°C) H₂O, NH₄Cl and supersaturated solutions of CO₂ (24°C and 33°C). The importance of peripheral carbonic anhydrase was tested 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 CO₂ were significantly inhibited by acetazolamide while the responses to thermal stimuli and NH₄Cl were not. The results support a role for carbonic anhydrase in trigeminal responses to CO₂. Furthermore, the results suggest that intraepithelial acidification mediated by carbonic anhydrase may be the basis for sensitivity to CO₂.