Effects of microinjected carbachol on the antinociceptive response to noxious heat stimuli.
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 (NRGCalpha) 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 micro g/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 micro g/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 micro g/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/NRGCalpha.
Abe
Kenji
K
Department of Neuroscience, Showa Pharmaceutical University, Machida, Tokyo, Japan.
Kikuta
Jun
J
Kato
Masatoshi
M
Ishida
Kota
K
Shigenaga
Toshiro
T
Taguchi
Kyoji
K
Miyatake
Tadashi
T
D000700:Analgesics / Q000008:administration & dosage*; D000818:Animals; D002217:Carbachol / Q000008:administration & dosage*; D006358:Hot Temperature / Q000009:adverse effects*; D008297:Male; D008845:Microinjections / Q000379:methods*; D010147:Pain Measurement / Q000187:drug effects* / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D011950:Receptors, Cholinergic / Q000502:physiology
D000700:Analgesics; D011950:Receptors, Cholinergic; D002217:Carbachol