Journal of pharmacological sciences
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The present study was undertaken to clarify how spinal muscarinic receptors are involved in the antinociceptive effects in thermal stimulation. Intrathecal (i.t.) injection of the muscarinic agonist McN-A-343 inhibited the tail-flick response to noxious thermal stimulation in a dose-dependent manner (31.5 - 63.0 nmol). This McN-A-343-induced antinociceptive effect was dose-dependently inhibited by intrathecal (i.t.) injection of a nonselective muscarinic receptor antagonist atropine, the selective muscarinic M(1) antagonist pirenzepine, or the M(4) antagonist himbacine. ⋯ In contrast, the selective muscarinic M(2) antagonist methoctramine did not inhibit the antinociceptive effects of McN-A-343. In addition, the McN-A-343-induced antinociceptive effect was attenuated by i.t. injection of the GABA(A) antagonist bicuculline, but not by injection of the GABA(B) antagonist CGP35348. These results suggest that McN-A-343 produces its antinociceptive effect on the response to thermal stimulation via spinal muscarinic M(1) receptors and, at least in part, through neuronal pathways involving spinal GABA(A) receptors in mice.