QUINOLINATE DIFFERENTIATES BETWEEN FOREBRAIN AND CEREBELLAR NMDA RECEPTORS

The potency of N-methyl-D-aspartate (NMDA), ibotenate, L-glutamate and quinolinate for inhibiting [H-3]L-glutamate binding to rat brain NMDA receptors was determined by quantitative autoradiography. In contrast to NMDA, ibotenate and L-glutamate, quinolinate more potently displaced binding in forebrain regions than in the cerebellum. Of all drug-region combinations, only quinolinate affinity in the cerebellum was best described by a two-affinity component model (K(i) = 24 and 275-mu-M; 45% high affinity). The cerebellum appears to contain a unique quinolinate-insensitive NMDA receptor subtype.