Kainic acid, an anthelmintic extracted from seaweed, is a known neurotoxic agent and its effect upon CNS was widely studied. In the present study, the scala tympani of 13 guinea pigs was perfused with various dosages of kainic acid and its effects upon the AP and CM were examined. The CM was not affected by Kainic acid less than 2 nmol but when dosages more than 3 nmol was given, it was reduced by 50% or more in 5 out of 7 performances. The dose-dependent reduction was obtained in the AP amplitude. The intencity-function curve revealed that the initial change was the loss of so called “L-part”. As the dosage was increased, “H-part” was also reduced and finally no potential was recorded. Although the amplitude was severely depressed, the AP latency was not prolonged. The results obtained in the present study strongly suggest that the site of action of Kainic acid is in the cochlear neuron and the AP latency is not prolonged in neural deafness.
