Pharmacologic antagonism of the oral aversive taste-directed response to capsaicin in a mouse brief access taste aversion assay.

Chemosensory signaling by the tongue is a primary determinant of ingestive behavior and is mediated by specific interactions between tastant molecules and G protein-coupled and ion channel receptors. The functional relationship between tastant and receptor should be amenable to pharmacologic methods and manipulation. We have performed a pharmacologic characterization of the taste-directed licking of mice presented with solutions of capsaicin and other transient receptor potential vanilloid-1 (TRPV1) agonists using a brief access taste aversion assay. Dose-response functions for lick-rate suppression were established for capsaicin (EC(50) = 0.5 microM), piperine (EC(50) = 2 muM), and resiniferatoxin (EC(50) = 0.02 microM). Little or no effect on lick rate was observed in response to the full TRPV1 agonist olvanil. Capsaicin lick rates of wild-type and transient receptor potential melastatin-5 (TRPM5) knockout mice were equivalent, indicating that TRPM5, a critical component of aversive signaling for many bitter tastants, did not contribute to the capsaicin taste response. The selective TRPV1 antagonists N-(4-tertiarybutylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide (10 microM) and (E)-3-(4-t-butylphenyl)-N-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)acrylamide (AMG9810) (10 microM) effectively blocked capsaicin- and piperine-mediated lick suppression. However, (E)-3-(4-chlorophenyl)-N-(3-methoxyphenyl)-N-phenylprop-2-enamide (SB 366791) and capsazepine, also TRPV1 antagonists, were without effect at test concentrations of up to 30 and 100 microM, respectively. Our results demonstrate that TRPV1-mediated oral aversiveness presents a pharmacologic profile differing from what has been reported previously for TRPV1 pain signaling and, furthermore, that aversive tastes can be evaluated and controlled pharmacologically.