Effects of picrotoxin upon response characteristics of wide dynamic range neurons in the spinal cord of cat and monkey.

The effects of a subconvulsive dose of picrotoxin (0.5 mg/kg) upon response characteristics of wide dynamic range (WDR) neurons in the spinal dorsal horn were investigated in cats and Japanese macaques. After intravenous administration of picrotoxin, the low threshold mechanoreceptive field of WDR neurons were expanded, and the high threshold surround of the receptive field disappeared. Concomitantly, responses of WDR neurons to noxious heat stimulation were abolished. It was suggested that picrotoxin may close the presynaptic gate for nociceptive input to WDR neurons, enhancing excitatory action of tactile input on the same neurons.