Cyclothiazide unmasks AMPA-evoked stimulation of [3H]-L-glutamate release from rat hippocampal synaptosomes.

The effect of alpha-amino-3-hydroxy-5-methylisoxazolepropionate (AMPA) on Ca(2+)-sensitive, tetrodotoxin (TTX)-insensitive K(+)-stimulated 3H]-L-glutamate release from rat hippocampal synaptosomes was determined. AMPA in the presence, but not in the absence of cyclothiazide, a drug which blocks AMPA receptor desensitization, elicited a dose-dependent increase in K(+)-stimulated 3H]-L-glutamate release but had no effect on basal release. The AMPA/cyclothiazide stimulation was blocked by CNQX and by GYKI 52466, an antagonist at the cyclothiazide site. These results indicate that AMPA receptors are present on presynaptic terminals and suggest that they may play a role in the regulation of neurotransmitter release.