Interactions between topically applied excitatory amino acids on rat cerebral cortex: discrimination by pentobarbitone.

The interaction between the effects of topically applied excitatory amino acid receptor agonists on the somatosensory evoked potentials (SEPs) were examined in urethane-anaesthetised rats. Preceding application of N-methyl-D, L-aspartic acid (NMDLA) prevented the effects of quinolinic acid or kainic acid but not those of carbachol or KCl. Similarly, quisqualic acid prevented the effects of NMDLA or kainic acid but not that of carbachol. Pentobartitone suppressed the inhibitory effect of quisqualic acid on NMDLA responses without altering the NMDLA response itself. It is concluded that an apparent desensitisation phenomenon occurs between the excitatory amino acids, distal to the receptor site.