Residual chemosensory capabilities in double P2X2/P2X3 purinergic receptor null mice: intraoral or postingestive detection?

Mice lacking the purinergic receptors, P2X2 and P2X3 (P2X2/P2X3(Dbl-/-)), exhibit essentially no tastant-evoked activity in the chorda tympani and glossopharyngeal nerves and substantial loss of tastant-evoked behavior as measured in long-term intake experiments. To assess whether the residual chemically driven behaviors in these P2X2/P2X3(Dbl-/-) mice were attributable to postingestive detection or oropharyngeal detection of the compounds, we used brief access lickometer tests to assess the behavioral capabilities of the P2X2/P2X3(Dbl-/-) animals. The P2X2/P2X3(Dbl-/-) mice showed avoidance to high levels (10 mM quinine and 10-30 mM denatonium benzoate) of classical "bitter"-tasting stimuli in 24-h, 2-bottle preference tests but minimal avoidance of these substances in the lickometer tests, suggesting that the strong avoidance in the intake tests was largely mediated by post-oral chemosensors.