Abstract
The present study was performed to explore the involvement of opioid receptors in the calcitonin gene‐related peptide 8‐37 (CGRP8‐37, an antagonist of CGRP receptor)‐induced inhibition of the activity of wide‐dynamic‐range (WDR) neurons in the spinal dorsal horn of rats. Extracellular recording was performed with a multibarrelled glass micropipette, and the chemicals were delivered by micro‐iontophoresis. The discharge frequency of WDR neurons was evoked by subcutaneous electrical stimulation applied to the ipsilateral hindpaw. Iontophoretic application of CGRP8‐37 by an ejection current of 160 nA induced significant inhibition of the discharge frequency of WDR neurons. The inhibitory effect of CGRP8‐37 on the activity of WDR neurons was attenuated by later iontophoretic application of the opioid antagonist naloxone. Furthermore, the effect of CGRP8‐37 was attenuated by either iontophoretic application of the kappa‐receptor antagonist nor‐binaltorphimine (nor‐BNI) or the mu‐receptor antagonist β‐funaltrexamine (β‐FNA) but not by the delta‐receptor antagonist naltrindole. The results indicate that kappa‐ and mu‐opioid receptors on the membrane of WDR neurons are involved in the modulation of CGRP8‐37‐induced antinociception in dorsal horn of the spinal cord in rats. © 2004 Wiley‐Liss, Inc.