title: Differential effects of various doses of morphine and naloxone on two nociceptive test thresholds in arthritic and normal rats.
abstract: In an attempt to clearly gauge the influence of the test used on opioid effects, the present study systemically compares the effects of various doses of morphine and naloxone with 2 differentially integrated tests: a suprasegmentally integrated test, the vocalization threshold to paw pressure and a spinally coordinated reflex, the paw withdrawal to pressure. In both normal and arthritic rats, clear differential effects of the drugs were observed: low doses of morphine (0.3 and 1 mg/kg i.v.) produced marked effects on the vocalization test, especially in arthritic rats, while it was less effective on the paw withdrawal test. Naloxone and morphine at extremely low doses (3-10 micrograms/kg, and 6 micrograms/kg i.v. respectively) clearly produced marked effects on the vocalization test, but failed to modify the paw withdrawal threshold in arthritic rats. By contrast, a high dose of naloxone (1 mg/kg i.v.) induced a comparable decrease in thresholds in both tests. This comparative study clearly shows the interest of using the vocalization threshold to paw pressure as a nociceptive test for evaluation of the antinociceptive effect of opioids. In addition, it provides useful information for a better understanding of the complex effects of morphine and the opioid antagonist naloxone in arthritic rats.
authors.affiliation: Unité de Recherches de Physiopharmacologie du Système Nerveux, INSERM U161, 75014 Paris France.
authors.forename: V
authors.initials: V
authors.lastname: Kayser
authors.forename: G
authors.initials: G
authors.lastname: Guilbaud
mesh_terms: D000818:Animals; D001168:Arthritis / Q000503:physiopathology*; D004305:Dose-Response Relationship, Drug; D007275:Injections, Intravenous; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D009619:Nociceptors / Q000502:physiology*; D010812:Physical Stimulation; D011312:Pressure; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D012684:Sensory Thresholds; D014828:Vocalization, Animal
chemical_list: D009270:Naloxone; D009020:Morphine