Greater Superficial Petrosal Nerve Transection in Rats does not Change Unconditioned Licking Responses to Putatively Sweet Taste Stimuli

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Abstract
The greater superficial petrosal nerve (GSP), innervating taste buds in the palate, is known to be exceptionally responsive to sucrose, especially compared with the responsiveness of the chorda tympani nerve (CT). However, whereas transection of the CT (CTX) alone has little or no effect on unconditioned licking responses to many “sweet” stimuli, the impact of GSP transection (GSPX) alone is equivocal. To further examine the role of the GSP on licking responses to putatively sweet-tasting substances, brief-access taste tests were conducted in nondeprived rats before and after sham surgery (SHAM) or CTX or GSPX. A range of concentrations of sucrose, L-alanine, glycine, and L-serine, with and without 1.0 mM inosine monophosphate (IMP) added, were used. All groups showed significant concentration-dependent increases in licking to all stimuli presurgically and postsurgically. CTX decreased licking responses relative to SHAM rats in the first sucrose test. There was also a group × concentration interaction for L-alanine, but post hoc tests did not reveal its basis. Other than this, there were no significant differences among the surgical groups. Interestingly, rats with GSPX tended to initiate fewer trials than SHAM rats. Overall, after GSPX, the remaining gustatory nerves are apparently sufficient to maintain concentration-dependent licking responses to all stimuli tested here. The disparity between our results and others in the literature where GSPX reduced licking responses to sucrose is possibly related to differences in surgical technique or test trial duration.