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

Two-bottle intake tests and taste reactivity (TR) tests were used to reveal whether changes in ingestive behavior would follow bilateral section of either the chorda tympani (CT) or the glossopharyngeal (GP) nerve. Rats received two-bottle intake tests to compare 24-h ingestion of water to that of NaCl, MgCl₂, quinine, or sucrose. Prior to each long-term intake test, rats received a 1 min, 1 ml intraoral infusion of the same chemical stimulus. Ingestive and aversive oral motor responses elicited by these 1 ml infusions were videotaped and subsequently analyzed. GP-section did not alter quinine or sucrose preference; overall, preference of MgCl₂ and NaCl was also similar to controls. In contrast, TR tests in GP-sectioned rats revealed that most quinine, MgCl₂ and NaCl stimuli elecited significantly fewer aversive oral motor responses. In addition, the latency of aversive responses to these 3 chemical stimuli was increased for these rats. Intake-based preference tests failed to show any difference between rats with CT nerve section and controls. In TR tests, however, CT-sectioned rats displayed significantly fewer ingestive oral motor responses to NaCl, MgCl₂, and quinine than controls. Neither sucrose intake nor sucrose-elicited TR were altered by CT or GP nerve section. This report confirms the failure of long-term intake tests to uncover behavioral deficits following the section of gustatory nerves. In contrast, the use of a different behavioral test makes clear for the first time that gustatory nerve section has dramatic consequences on ingestive behavior. The examination of taste elicited oral motor behaviors reveals a coherent and nerve specific pattern of neurological deficit following peripheral nerve section.