Involvement of endogenous opioids and ATP-sensitive potassium channels in the mediation of carbachol-induced antinociception at the spinal level: A behavioral study in rats

The effects of intrathecally administered (i.t.) atropine, glibenclamide, a blocker of ATP-sensitive potassium channels, or naloxone on the antinociception produced by i.t. carbachol or morphine were observed in rats by tail-flick (TF) test. The results showed that: (1) i.t. carbachol produced a dose-dependent antinociception and it could be antagonized by i.t. atropine; (2) the antinociception produced by i.t. carbachol could be blocked dose-dependently by id. glibenclamide or i.t. naloxone; (3) the antinociception produced by i.t. morphine could be blocked dose-dependently by i.t. glibenclamide, but not by i.t. atropine. The results suggest that the antinociception produced by activation of muscarinic receptors at the spinal level might be mediated by endogenous opioids and ATP-sensitive potassium channels in a cascade form.