Effect of different concentrations of iontophoretic nociceptin on distinct classes of nociceptive neurons in rat spinal cord.

Iontophoretically applied nociceptin (NC) was tested at different concentrations on the activity of spinal nociceptive specific (NS) and wide dynamic range (WDR) neurons. Low NC dosages inhibited the noxious response of NS neurons, higher dosages inhibited the noxious responses of the WDR neurons but had little effect on the non-noxious response. Naloxone did not antagonize the NC effect. Thus, appropriate dosages of NC may be selective, both for neuronal classes and for sensory modalities.