Zinc contained in the neurons of central nervous system is activity-dependently released and then attenuates NMDA (N-methyl-D-aspartate)-induced neurotoxicity while augmenting non-NMDA-induced neurodegeneration. Zinc also has been reported to produce antinociceptive action on the inflammation- and nerve injury-induced hyperalgesia in the behavioral test. In this study, we investigated the effects of zinc on the responses of dorsal horn cells to NMDA, kainate and graded electrical stimulation of C-fibers. In the majority of WDR cells (70.6%), zinc current-dependently inhibited WDR cell responses to NMDA and in the remaining cells, produced biphasic responses; excitation followed by inhibition. Zinc augmented the responses of WDR cells to iontophoretical application of kainate. The dominant effect of Zn2⁢ on the responses of WDR cells to C-fiber stimulation was excitatory, but inhibition, excitation-inhibition and no change of the responses to C-fiber stimulation were induced. Ca2⁢-EDTA antagonized the excitatory or inhibitory effects of Zn2⁢ on the WDR cell responses. These experimental findings suggest that Zn2⁢ modulates the transmission of sensory