GABA enhancement of [3H]dopamine release from slices of rat striatum: dependence on slice size

The effect of GABA on potassium-evoked tritium release from two sizes of ribbon of rat striatum previously loaded with [3H]dopamine was studied. GABA had no effect on the release of tritium from 100 x 100 mum ribbons but produced a dose-related enhancement of potassium-evoked tritium release from 250 x 250 mum ribbons. The enhancement was unaffected by the presence of bicuculline or picrotoxin but was antagonised by tetrodotoxin. The effect of GABA was not mimicked by the GABA agonists muscimol or baclofen. The possible involvement of an interneurone is discussed. From antagonist studies the neurotransmitter released by the postulated interneurone did not appear to be acetylcholine, 5-hydroxytryptamine, glycine, glutamate or enkephalin.