摘要：Injecting muscarinic receptor agonists into a specific area of the brainstem produces an antinociceptive response. The present study investigates whether direct injections of the cholinergic agonist, carbachol, into the rat nucleus reticularis gigantocellularis (NRGC)/nucleus reticularis gigantocellularis alpha (NRGCα) of the rostral ventrolateral medulla evokes antinociception, and then examines the interference action of cholinergic antagonists in rats. Microinjections of carbachol (0.75, 1.5, 3 μg/site) prolonged hot plate (HP) and tail flick (TF) responses to noxious heat stimuli in a dose-dependent manner. The level of carbachol-induced antinociception during the HP and TF tests reached a maximum at 5—15 min after carbachol administration in all groups. Thereafter, the peak level progressively decreased and reached the baseline by the end of the experiment. Antinociception induced by carbachol at 3 μg/site was attenuated by the prior administration of the muscarinic receptor antagonist, atropine (200, 500 ng/site). On the other hand, the nicotinic autonomic ganglion blocker, mecamylamine (1, 3 μg/site), did not affect subsequent carbachol-induced antinociception. These results suggest that the antinociceptive effects induced by a microinjection of carbachol depend on muscarinic, but not nicotinic, mechanisms within the rat NRGC/NRGCα.
