We investigated the effects of spinal nociceptin on formalin-induced spinal sensitization and examined the role of the opioidergic, alpha 2- adrenergic and muscarinic cholinergic receptors in the nociceptin-produced suppression of spinal sensitization. The results demonstrated that spinal nociceptin suppressed the formalin-induced spinal sensitization in a dose- dependent manner (1, 5 and 10 nmol). The inhibitory effect of 10 nmol of nociceptin on spinal sensitization, was readily antagonized by naltrexone, but not by atropine or yohimbine. Each of the antagonists, naltrexone, atropine or yohimbine, alone had no effect on the formalin-induced spinal sensitization. Our results show that spinal nociceptin elicits dose- dependent, naltrexone-reversible suppression of spinal sensitization evoked by injection of formalin.
- Formalin test
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