Alpha2-adrenoceptor antagonists enhance responses of dorsal horn neurones to formalin induced inflammation.

Intrathecally applied alpha2-adrenoceptor antagonists atipamezole, idazoxan and yohimbine had no significant effect on any neuronal response in normal animals. In contrast, all three antagonists (100 microg) significantly increased the area under the curve of the total response to formalin, especially the second phase. Our results suggest the alpha2-adrenoceptor-mediated noradrenergic inhibitory system in the spinal cord is dormant under normal conditions, but controls both the magnitude and duration of the neuronal responses to subcutaneous injection of formalin.