LOW-AFFINITY KAINATE RECEPTORS AND LONG-LASTING DEPRESSION OF NMDA-RECEPTOR-MEDIATED CURRENTS IN RAT SUPERFICIAL DORSAL HORN

In an in vitro spinal cord slice preparation whole cell electrophysiol ogical recordings of rat superficial dorsal horn neurons responding di fferentially to glutamate (Glu) and N-methyl-D-aspartate (NMDA) were i nvestigated systematically for the role of kainate (KA) receptors in m odulating their activity. In these neurons, coapplication of Glu and N MDA, as well as application of Glu immediately before NMDA, induced lo ng- and short-lasting depressions of NMDA-induced currents as well as depression of NMDA-receptor-mediated excitatory postsynaptic currents. KA applied before NMDA mimicked Glu-induced attenuating effects. Furt hermore, the low-affinity KA receptor antagonist 5-nitro-6,7,8,9-tetra hydrobenzo[G] indole-2,3-dione-3-oxime potentiated Glu-induced NMDA-re ceptor-mediated currents In neurons responding differentially to Glu a nd NMDA. These results provide evidence for a novel mechanism, which m ay relate to classical long-term depression, involving low-affinity KA receptors in long-lasting modulation of NMDA-receptor-mediated curren ts. This implies a physiological role of KA receptors in longterm modu lation of sensory transmission in the superficial dorsal horn of rat s pinal cord.