Combined Glossopharyngeal and Chorda Tympani Nerve Transection Elevates Quinine Detection Thresholds in Rats (Rattus norvegicus )

Using a conditioned shock avoidance procedure, behavioral quinine hydrochloride thresholds were measured before and after glossopharyngeal (GLX), chorda tympani (CTX), or combined glossopharyngeal and chorda tympani (GLX + CTX) transection, as well as after sham surgery. In Experiment 1, thresholds in the sham, CTX, and GLX rats ( Rattus norvegicus ) either improved (lowered) or remained the same after surgery. In Experiment 2, GLX + CTX caused a pronounced 1.5 log 10 unit increase in presurgically measured thresholds. Neither the glossopharyngeal nor the chorda tympani nerve is necessary for normal sensitivity to low quinine concentrations provided the other is intact. When both of these nerves are transected, however, the remaining afferent input is not sufficient to maintain normal detection performance.