The action of putative neurotransmitter substances in the cat labyrinth.

Possible neurotransmitter candidates were tested in the labyrinth of the cat with the aid of microiontophoretic techniques. Depending on the recording site, spontaneous regular or irregular fibre activity was obtained in the subsynaptic region of the macula sacculi. Ejection of GABA enhances the firing rate, whereas acetylcholine reduces the spontaneous activity. A similar application of glycine and proline produced no effect. The action of GABA was specifically blocked by the GABA antagonists bicuculline and picrotoxin. The alkaloids further induced a decrease in the spontaneous activity which lasted for several minutes.