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 gamma-[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 microM. Quisqualate was more effective than kainate in the lower concentration range but less effective at concentrations at which its releasing activity was maximal (approximately 50 microM). N-Methyl-D-aspartic acid and dihydrokainate (100 microM) did not stimulate [3H]GABA release from cultured astrocytes. L-Glutamic acid (20-100 microM) 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 microM) 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 microM). 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.