The contribution of gustatory nerve input to oral motor behavior and intake-based preference. II. Effects of combined chorda tympani and glossopharyngeal nerve section in the rat

Two-bottle preference and taste-elicited oral motor responses were examined to determine whether the total lingual gustatory denervation that results from combined bilateral chorda tympani (CTX) and glossopharyngeal nerve section (GPX) would (a) alter the ingestive behavior of the rat and (b) if altered, whether the pattern of deficit revealed would be similar to or different from that obtained by sectioning each of the individual nerves separately. Remarkably, intake-based preference was unaffected by an ∼80% reduction in taste receptors. Lingual gustatory denervation failed to affect the preference for any of the normally-preferred stimuli. Preference for only two of the 8 normally-avoided solutions was increased following the combined nerve cuts. In contrast, examination of oral motor taste-reactivity responses revealed that combined nerve sections significantly reduced the number of ingestive responses elicited by 5 of 6 normally-preferred and 5 of 8 normally-avoided stimuli. In addition, the pattern of deficits in taste-elicited oral motor responses resulting from the combined section was different from that predicted by summing the effects of the individual nerve sections. We had shown that CTX did not alter aversive behavior to quinine whereas GPX did reduce these responses but did not affect their concentration dependence. Neither CTX nor GPX affected oral motor responses elicited by sucrose. Combined nerve section, by contrast, completely eliminated the concentration-dependent increases in aversive responses to quinine and ingestive responses to sucrose and glycine. In fact, CTX + GPX profoundly reduced the oral motor behavior elicited by all of the chemical stimuli examined. Despite the changes in the pattern of taste-elicited oral motor behavior combined nerve section did not alter (a) the morphology or duration of individual responses, (b) the concentration-dependent increase in aversive responses elicited by MgCl₂, or (c) the potentiation in oral motor responses to water seen in water-deprived rats (Expt. 2).