Predominant role of the chorda tympani nerve in the maintenance of the taste pores: the influence of gustatory denervation in ear surgery

To divide or manipulate the chorda tympani in stapedotomy

The objective of this study is to determine the nature, duration and severity of chorda tympani symptoms in post-stapedotomy patients when the nerve has been known to have either sustained surgical manipulation or division. The study design was retrospective and blind, based at a tertiary Otology Referral Center (Gloucestershire Royal Hospital). All successive patients undergoing stapedotomy operated upon by the senior author (JMR) between November 1991 and October 1998 were included. The main outcome measures were postoperative graded dysgeusia (questionnaire) and post operative electrogustometry score, comparing the chorda tympani cut group and the chorda tympani preserved group. Sixty stapedotomies were performed in the study period. After a minimum interval of 8 months, questionnaire data were obtained in 55/60 (92%), and electrogustometry studies were carried out in 48/60 (80%). Symptoms of dysgeusia were experienced in the chorda tympani nerve cut (CC) group in 95% and in the chorda preserved (CP) group in 52%. For those with symptoms, duration was 6.7 months (+/-4.9 SD) and 3.4 months (+/-3.7 SD) for the CC and CP groups, respectively. From the electrogustometry data, after 8 months, the risk of total loss of response is significantly higher in CC patients (94%) than in CP patients (25%) (P = 0.0001). Also at 8 months, 54% of CP patients had normal ipsilateral electrogustometry responses compared with 6% in the CC group. In conclusion, cutting the chorda tympani results in significantly greater symptoms than when subjected to manipulation only, and these symptoms are likely to be more long lasting. Therefore, it is our recommendation that where possible the chorda be preserved. The risk of severe chorda symptoms when the chorda is cut is small (<5%). Preoperative consent to include dysgeusia is advised.

Chorda tympani nerve transection does not alter operant oral self-administration of ethanol in the rat

In experimental conditions, it has been suggested that taste factors may contribute to ethanol preference in rodents. The aim of the current study was to assess the effects of transection of a gustatory branch of the seventh cranial nerve, the chorda tympani (CT), on operant self-administration of ethanol in rats. Male Wistar rats were trained to lever press for 8% [volume/volume (vol./vol.)] ethanol solution. When 8% ethanol intake stabilized, the CT nerve was transected bilaterally in six subjects. Another group received sham operations. There were no between-group differences in terms of self-administration of 8% ethanol, either before or after surgery. In addition, self-administration of 2% and 4% ethanol, measured after surgery, did not differ between the groups. In a control experiment, two-bottle consumption of as well as preference for 0.625% [weight/volume (wt./vol.)] sucrose were significantly decreased in the lesioned subjects. The results may indicate that gustatory input of the CT nerve is not necessary for maintenance of operant oral self-administration of ethanol.