Actions of kynurenic acid and quinolinic acid in the rat hippocampus in vivo.

An iontophoretic study was made of the interaction of kynurenic acid with excitatory amino acids in the hippocampus and with the commissural input from the contralateral hippocampus in the rat. The results showed that kynurenic acid was an effective blocker of synaptic transmission in the hippocampus in vivo, adding further support to the idea that an excitatory amino acid is involved in neurotransmission in this structure. In addition there was an increase in the specificity of kynurenate as an antagonist of excitatory amino acids in the hippocampus compared with neocortex, with much more activity being shown toward the NMDA-preferring rather than the quisqualic acid-preferring receptor. Kynurenic acid was also able to distinguish partially between quinolinic acid and NMDA, supporting the possibility that two types of NMDA/quinolinate receptors exist in the hippocampus.