Pharmacology of the isolated semicircular canal: effect of GABA and picrotoxin.

We have investigated the proposal that gamma aminobutyric acid (GABA) is the afferent transmitter in the vestibular system using the isolated posterior semicircular canal of the bullfrog (Rana catesbeiana). This was done by examining the effects of GABA and picrotoxin on the evoked response of neural units in the posterior ampullar nerve. GABA had no effect on evoked response up to 1 mM, and inhibited the evoked response at 10 mM. Picrotoxin, a GABA antagonist, had no effect on evoked response between 5 microM and 100 microM. These results indicate that GABA is not the afferent transmitter in the vestibular system.