title: Paradoxical hyperalgesic effect of exceedingly low doses of systemic morphine in an animal model of persistent pain (Freund's adjuvant-induced arthritic rats).
abstract: The effects of exceedingly low doses of morphine (3-50 micrograms/kg i.v.) were studied upon the vocalization threshold induced by paw pressure in rats with Freund's adjuvant-induced arthritis. The highest dose used (50 micrograms/kg i.v.) clearly induced an analgesic effect. No significant modification of the vocalization threshold was observed with 30 micrograms/kg. By contrast, a significant hyperalgesic effect resulted with doses of 10 down to 3 micrograms/kg. Maximum hyperalgesia was observed with 6 micrograms/kg.
mesh_terms: D000818:Animals; D001169:Arthritis, Experimental / Q000503:physiopathology; D004305:Dose-Response Relationship, Drug; D006930:Hyperalgesia / Q000139:chemically induced / Q000503:physiopathology*; D006941:Hyperesthesia / Q000503:physiopathology*; D007275:Injections, Intravenous; D008297:Male; D009020:Morphine / Q000008:administration & dosage* / Q000378:metabolism; D009270:Naloxone / Q000494:pharmacology; D010146:Pain / Q000188:drug therapy / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains; D012684:Sensory Thresholds / Q000187:drug effects; D013997:Time Factors; D014828:Vocalization, Animal
chemical_list: D009270:Naloxone; D009020:Morphine