Glossopharyngeal nerve transection does not compromise the specificity of taste-guided sodium appetite in rats

Abstract

The chorda tympani nerve (CT) has been shown to be critical in the sodium-specific drinking behavior of sodium-depleted rats, but the role of other gustatory nerves and the contribution of the major salivary glands remain to be elucidated. In this study, rats received either bilateral section of the CT (CTX) or the glossopharyngeal nerve (GLX), extirpation of the sublingual and submaxillary salivary glands (DSAL), or sham surgery. After recovery, rats were sodium depleted with furosemide and tested for their licking responses to 0.05 and 0.3 M NaCl, KCl, CaCl2, and NH4Cl, as well as distilled water in an automated gustometer. Rats that received GLX maintained a specific sodium appetite comparable to controls despite denervation of approximately 64% of the taste buds. In contrast, compared with control rats, CTX and DSAL rats had altered response profiles, showing much smaller differences in licking to NaCl relative to the other stimuli. This was accompanied by a substantially lower lick rate in DSAL rats, raising the possibility that general licking impairments contributed to the decreased NaCl responsiveness in these rats. These findings imply that the CT, but not the glossopharyngeal nerve, is necessary for the maintenance of normal sodium-specific, taste-guided behavior under sodium deplete conditions.