RECOVERY OF CHORDA TYMPANI NERVE FUNCTION FOLLOWING INJURY

The chorda tympani (CT) nerve carries taste information from the anter ior tongue to the brain stem. Injury to the chorda tympani may result in loss or distortion of taste information. This study examined change s occurring in the hamster peripheral taste system during recovery fro m injury. The hamster chorda tympani nerve was crushed in the middle e ar and the animals were allowed to survive from 2 to 16 weeks. At 2 we eks, CT fibers had degenerated distal to the crush site. Up to 16 week s after crush, there were 67% fewer myelinated fibers in regenerated n erves than in controls. The mean area of the Ca2+-ATPase-stained core of the fungiform taste buds was significantly smaller than in controls 2 weeks after injury, but recovered to control values by 4 weeks. Ele ctrophysiological responses to taste stimuli were recorded from the ch orda tympani distal to the injury. No responses were seen after 2 week s; weak. and unstable responses were seen after 3 weeks. By 4-8 weeks, relative responses to taste stimuli were similar to control responses , but the variability of the responses to sucrose was significantly gr eater than that in controls. The frequency of responses to the water r inse following taste stimuli, particularly sucrose, was also greater i n the regenerated nerves. The abnormal electrophysiological responses to sucrose may be the result of the differential rate of return of fib er types and/or the transduction mechanisms. In some ways, recovery of the peripheral gustatory system after damage to the chorda tympani ne rve recapitulates the later stages of taste bud development. (C) 1996 Academic Press, Inc.