Abstract

This report describes the in vivo effects of the uptake carrier blockers 1-(4,4-diphenyl-3-butenyl)-3-piperidine carboxylic acid hydrochloride (SK&F 89976-A) and l- trans-pyrrolidine-2,4-dicarboxylate ( l- trans-PDC) on basal and K +-evoked extracellular levels of γ-aminobutyric acid (GABA), glutamate, aspartate and taurine in the hippocampus of anaesthetised rats, using the microdialysis technique. SK&F 89976-A increased extracellular GABA levels under K +-depolarised conditions and did not affect extracellular glutamate, aspartate and taurine levels, indicating its selective effect on GABA uptake. l- trans-PDC dose dependently increased basal and K +-evoked extracellular glutamate levels, and did not affect extracellular GABA levels, but increased basal aspartate and taurine levels. The K +-evoked release of GABA and glutamate, measured in the presence of both SK&F 89976-A and l- trans-PDC, was Ca 2+-dependent for about 50% and 65%, respectively. In contrast, the release of the putative amino acid transmitters aspartate and taurine was not Ca 2+-dependent. These results indicate that (1) in rat hippocampus uptake carriers actively regulate extracellular GABA and glutamate levels, (2) the GABA and glutamate released by K + was derived from both Ca 2+-dependent (presumably vesicular) and Ca 2+-independent (presumably cytosolic) pools, whereas aspartate and taurine release was exclusively from Ca 2+-independent pools.

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