Expression of Excitatory Amino Acid Receptors by Cerebellar Cells of the Type-2 Astrocyte Cell Lineage

Abstract: We have used postnatal rat cerebellar astrocyte-enriched cultures to study the excitatory amino acid receptors present on these cells. In the cultures used, type-2 astrocytes (recognized by the monoclonal antibodies A2B5 and LB1) selectively took up γ-³H]aminobutyric acid (³H]GABA) and released it when incubated in the presence of micromolar concentrations of kainic and quisqualic acids. The releasing effect of kainic acid was concentration dependent in the range of 5–100 μ M . Quisqualate was more effective than kainate in the lower concentration range but less effective at concentrations at which its releasing activity was maximal (∼50 μ M ). N -Methyl- d -aspartic acid and dihydrokainate (100 μ M ) did not stimulate ³H]GABA release from cultured astrocytes. l -Glutamic acid (20–100 μ M ) stimulated ³H]GABA release as effectively as kainate. The stimulatory effects of kainate and quisqualate on ³H]GABA release were completely Na⁺ dependent; that of kainate was also partially Ca²⁺ dependent. Kynurenic acid (50–200 μ M ) selectively antagonized the releasing effects of kainic acid and also that of l -glutamate; quisqualate was unaffected. Quisqualic acid inhibited the releasing effects of kainic acid when both agonists were used at equimolar concentrations (50 μ M ). d -³H]aspartate was taken up by both type-1 and type-2 astrocytes, but only type-2 astrocytes released it in the presence of kainic acid. Excitatory amino acid receptors with a pharmacology similar to that of the receptors present in type-2 astrocytes were also expressed by the immature, bipotential progenitors of type-2 astrocytes and oligodendrocytes.