Different characteristics of gustatory responses between the greater superficial petrosal and chorda tympani nerves in the rat

The integrated responses to gustatory stimuli applied to the soft palate were recorded from the greater superficial petrosal nerve (GSP) and were compared with those from the chorda tympani nerve (CT) innervating the anterior part of the tongue in the rat. Stimuli included various concentrations of NaCl, sucrose, HCl and quinine hydrochloride, and 0.5 M of six sugars. The inhibitory effects of amiloride on the responses to sodium salts, including various concentration of NaCl, 0.1 M sodium acetate and 0.01 M sodium saccharin, were also tested. Both the phasic and tonic responses to sugars in the GSP were significantly larger than those in the CT, whereas both responses to NaCl in the GSP were significantly smaller than those in the CT. Although amiloride at 50 mu M significantly depressed the phasic and tonic responses to NaCl with a wide range of concentration in the CT, little inhibitory effect was observed in the GSP. The tonic response to sodium acetate, when dissolved in amiloride solution, was depressed to 15% of the control in the CT, and slightly but significantly depressed to 70% in the GSP. These response characteristics of the CSP may play important roles in the processing of gustatory information.