Glutamate as the neurotransmitter of cerebellar granule cells in the rat: electrophysiological evidence.

1 Glutamate and the excitatory aminoacid antagonist, alpha-aminoadipic acid (alphaAA), have been applied by microiontophoresis to Purkinje cells in the rat cerebellum. 2 Glutemate produced excitation of Purkinje cells and alpha AA selectively reduced that excitation without affecting responses to acetylcholine or hydrogen ions. 3 Monosynaptic spikes were evoked in Purkinje cells by stimulating the parallel fibres. alpha AA had little effect on these spikes when applied alone. 4 When the Purkinje cell excitability was reduced by the iontophoresis of gamma-aminobutyric acid, alpha AA then produced railure of the monosynaptic spike on 10 of 13 Purkinje cells, in doses shown to be selectively antagonistic towards aminoacids. 5 These results support neurochemical evidence that glutamic acid may be the neurotransmitter released by granule cell parallel fibres.