title: Characterization of muscarinic receptor subtypes in the rostral ventrolateral medulla and effects on morphine-induced antinociception in rats.
abstract: The present study investigated the role of muscarinic receptor subtypes in the nucleus reticularis gigantocellularis/nucleus reticularis gigantocellularis alpha of the rat rostral ventrolateral medulla in morphine-induced antinociception. The antinociceptive effects of morphine were evoked by systemic administration or microinjection into the nucleus reticularis gigantocellularis/nucleus reticularis gigantocellularis alpha. Administration of morphine produced antinociception for hot plate and tail immersion responses to noxious heat stimuli. These effects were antagonized by prior exposure to naloxone and inhibited by mecamylamine pretreatment. Morphine-induced antinociception was significantly inhibited by atropine in a dose-dependent manner. Muscarinic toxin-1 and pirenzepine inhibited morphine-induced antinociception for both the hot plate and tail immersion tests. At a dose of 5 nmol/site, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) also inhibited morphine-induced antinociception, although low doses of this drug did not significantly affect hot plate test response latency when morphine was systemically administered. These results suggest that the antinociceptive effects induced by morphine in part involve the muscarinic M(1) and M(3) receptors of the rat nucleus reticularis gigantocellularis/nucleus reticularis gigantocellularis alpha.
authors.affiliation: Department of Neuroscience, Showa Pharmaceutical University, 3-3165 Higashitamagawagakuen, Machida, 194-8543, Tokyo, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Abe
authors.forename: Kyoji
authors.initials: K
authors.lastname: Taguchi
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Kato
authors.forename: Iku
authors.initials: I
authors.lastname: Utsunomiya
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Chikuma
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hojyo
authors.forename: Tadashi
authors.initials: T
authors.lastname: Miyatake
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D003959:Diamines / Q000494:pharmacology; D008297:Male; D008464:Mecamylamine / Q000494:pharmacology; D008526:Medulla Oblongata / Q000187:drug effects* / Q000502:physiology; D008845:Microinjections; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010147:Pain Measurement; D010880:Piperidines / Q000494:pharmacology; D010890:Pirenzepine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D043643:Receptor, Muscarinic M1 / Q000037:antagonists & inhibitors*; D043585:Receptor, Muscarinic M2 / Q000037:antagonists & inhibitors*; D043587:Receptor, Muscarinic M3 / Q000037:antagonists & inhibitors*; D013997:Time Factors
chemical_list: D000701:Analgesics, Opioid; D003959:Diamines; D009292:Narcotic Antagonists; D010880:Piperidines; D043643:Receptor, Muscarinic M1; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D009270:Naloxone; D010890:Pirenzepine; D008464:Mecamylamine; D009020:Morphine; D001285:Atropine; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; C054938:methoctramine