Glutamate Receptor Subtypes in Cultured Cerebellar Neurons: Modulation of Glutamate and γ‐Aminobutyric Acid Release

Using cerebellar, neuron‐enriched primary cultures, we have studied the glutamate receptor subtypes coupled to neurotransmitter amino acid release. Acute exposure of the cultures to micromolar concentrations of kainate and quisqualate stimulated D‐[ 3 H]aspartate release, whereas N ‐methyl‐D‐aspartate, as well as dihydrokainic acid, were ineffective. The effect of kainic acid was concentration dependent in the concentration range of 20–100 μM. Quisqualic acid was effective at lower concentrations, with maximal releasing activity at about 50 μM. Kainate and dihydrokainate (20–100 μM ) inhibited the initial rate of D‐[ 3 H]aspartate uptake into cultured granule cells, whereas quisqualate and N ‐methyl‐DL‐aspartate were ineffective. D‐[ 3 H]Aspartate uptake into confluent cerebellar astrocyte cultures was not affected by kainic acid. The stimulatory effect of kainic acid on D‐[ 3 H]aspartate release was Na + independent, and partly Ca 2+ dependent; the effect of quisqualate was Na + and Ca 2+ independent. Kynurenic acid (50–200 μM ) and, to a lesser extent, 2,3‐ cis ‐piperidine dicarboxylic acid (100–200 μM ) antagonized the stimulatory effect of kainate but not that of quisqualate. Kainic and quisqualic acid (20–100 μM ) also stimulated γ‐[ 3 H]aminobutyric acid release from cerebellar cultures, and kynurenic acid antagonized the effect of kainate but not that of quisqualate. In conclusion, kainic acid and quisqualic acid appear to activate two different excitatory amino acid receptor subtypes, both coupled to neurotransmitter amino acid release. Moreover, kainate inhibits D‐[ 3 H]aspartate neuronal uptake by interfering with the acidic amino acid high‐affinity transport system.