Excitatory amino acid antagonists and endogenous aspartate and glutamate release from rat hippocampal slices.

1. The effect of excitatory amino acid agonists and antagonists on the efflux of endogenous aspartate and glutamate from the rat hippocampus in vitro was studied. 2. None of the compounds tested had any effect on the basal efflux of endogenous aspartate and glutamate. 3. 2-Amino-5-phosphonovaleric acid (APV), 2-amino-7-phosphonoheptanoic acid (APH) and MK-801 all reduced the potassium-evoked efflux of aspartate and glutamate by between 14.9% and 34.3% (P less than 0.05). 4. The depression of efflux brought about by APV was still observed in the presence of tetrodotoxin. 5. Neither N-methyl-D,L-aspartate nor quinolinic acid had any effect on the potassium-evoked efflux of aspartate and glutamate. 6. These results imply the existence of presynaptic amino acid receptors that are capable of modulating the efflux of endogenous aspartate and glutamate.