Characterization of excitatory amino acid receptors in cultured chick cerebellar neurons.

In order to characterize excitatory amino acid receptors in cultured chick cerebellar neurons, the effects of amino acid agonists on the input resistance and the antagonist specificity of the depolarization induced by each agonist were intracellularly studied. In Mg-containing medium, glutamate (especially at low doses), aspartate and N-methyl-D-aspartate not only decreased the input resistance at depolarized membrane potentials but also increased it at around the resting potential. In Mg-free medium, glutamate (high and low doses) and all other agonists simply decreased the input resistance. The effects of antagonists on amino acid-induced depolarizations in Mg-free medium were as follows: Mg and alpha-aminoadipate blocked N-methyl-D-aspartate and aspartate most strongly, glutamate and kainate moderately, and quisqualate only slightly; 2-amino-4-phosphonobutyrate antagonized N-methyl-D-aspartate most strongly, aspartate moderately and others mildly; 2-amino-5-phosphonovalerate blocked aspartate most strongly and others mildly; gamma-D-glutamylglycine blocked kainate most strongly and others moderately; and kynurenate was rather nonselective but most strongly antagonized N-methyl-D-aspartate and aspartate. These results suggest that all receptor subtypes (N-methyl-D-aspartate-, quisqualate- and kainate-types) are present in cultured chick cerebellar neurons, but their antagonist specificities are different from those in other central neurons, and also that glutamate at a low dose activates N-methyl-D-aspartate receptors, while it acts on quisqualate receptors at a high dose.