title: Influence of selective alpha 2-adrenergic agents on mustard oil-induced central hyperalgesia in rats.
abstract: The effects of systemically administered medetomidine, an alpha 2-adrenoceptor agonist, and atipamezole, an alpha 2-adrenoceptor antagonist, on mustard oil-induced central hyperalgesia were determined in unanesthetized rats. The mechanical threshold for eliciting a hindlimb flexion reflex (a nocifensive response) was determined with a series of calibrated monofilaments. Under control conditions mustard oil produced a significant decrease of the hindlimb withdrawal threshold for mechanical stimuli applied to a distal site in the hindlimb, whereas the corresponding threshold in the (untreated) contralateral side was not changed. Medetomidine administered 12 min prior to mustard oil treatment produced a significant dose-dependent (3-30 micrograms/kg s.c.) attenuation of the mustard oil-induced threshold decrease whereas the withdrawal threshold of the contralateral (untreated) hindlimb was not changed at these low doses. The antinociceptive effect of medetomidine (10 micrograms/kg) administered 12 min prior to the mustard oil treatment was not significantly stronger than the effect of medetomidine administered immediately after the mustard oil treatment. Atipamezole at a high (1000 micrograms/kg) or a low (10 micrograms/kg) dose did not influence the mustard oil-induced threshold decrease, whereas at an intermediate dose (100 micrograms/kg) atipamezole alone had a significant antinociceptive effect on mustard oil-induced hyperalgesia. The results indicate that medetomidine produces a selective attenuation of central hyperalgesia at doses which are sub-antinociceptive in intact rats. A pre-emptive treatment with medetomidine did not produce stronger antinociception than medetomidine treatment after the development of hyperalgesia. An alpha 2-adrenoceptor antagonist, atipamezole, attenuated central hyperalgesia in a non-monotonic fashion.
authors.affiliation: Department of Physiology, University of Helsinki, Finland.
authors.forename: H
authors.initials: H
authors.lastname: Mansikka
authors.forename: A
authors.initials: A
authors.lastname: Pertovaara
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D006930:Hyperalgesia / Q000139:chemically induced / Q000188:drug therapy*; D007093:Imidazoles / Q000494:pharmacology*; D008297:Male; D020926:Medetomidine; D009149:Mustard Plant; D009619:Nociceptors / Q000187:drug effects; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects; D010936:Plant Extracts / Q000633:toxicity; D010938:Plant Oils; D051381:Rats; D017208:Rats, Wistar; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000502:physiology; D012018:Reflex / Q000187:drug effects
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D007093:Imidazoles; D010936:Plant Extracts; D010938:Plant Oils; D018341:Receptors, Adrenergic, alpha-2; C050701:atipamezole; D020926:Medetomidine; C027793:mustard oil