Characterization of glutamate and [3H]D-aspartate outflow from various in vitro preparations of the rat hippocampus.

The characteristics of high-K+ and electrically evoked endogenous glutamate and [3H]D-aspartate release have been studied in multiple in vitro preparations of the rat hippocampus (transverse slices, granule cells cultures, synaptosomes and messy fibre synaptosomes) under similar experimental conditions. High external K+ concentrations evoked [3H]D-aspartate and endogenous glutamate overflow in a concentration-dependent manner in all preparations (except it was not possible to measure endogenous glutamate outflow from granule cells). This effect was tetrodotoxin-insensitive but partially calcium-dependent. In slices, field electrical stimulation evoked an overflow of endogenous glutamate, but not of [3H]D-aspartate, in a frequency-dependent manner. This effect was concentration-dependently amplified by the glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid (t-PDC). The electrically evoked glutamate overflow in the presence of t-PDC was tetrodotoxin-sensitive and calciu...