Parallel antagonism of synaptic transmission and kainate/quisqualate responses in the hippocampus by piperazine-2,3-dicarboxylic acid analogs.

A new series of potent antagonists of excitatory neurotransmission in the rat hippocampus has been identified. These derivatives of piperazine-2,3-dicarboxylate (PzDA) include the most potent acidic amino acid antagonists yet described for Schaffer collateral-commissural EPSPs. These antagonists also effectively block excitatory synaptic responses recorded in the lateral and medial perforant pathways and in the mossy fiber pathway. The PzDA derivatives also block focal depolarizations produced by kainate, quisqualate, and N-methyl-D-aspartate. N-methyl-D-aspartate responses are more susceptible to inhibition by PzDA derivatives, although the spectrum of antagonism of N-methyl-D-aspartate and synaptic responses by PzDA derivatives is not parallel. However, the antagonism of kainate and quisqualate responses by PzDA derivatives shows the same rank order of potency as synaptic responses. These data indicate that synaptic receptors in the hippocampus have a pharmacologic profile similar to that of kainate or quisqualate receptors.