Behavioural and electrophysiological studies on the paradoxical antinociceptive effects of an extremely low dose of naloxone in an animal model of acute and localized inflammation

Experimental Brain Research
V KayserG Guilbaud

Abstract

We have previously described the paradoxical antinociceptive effect of low doses of an opiate antagonist, naloxone, in rats suffering from chronic arthritis induced by Freund's adjuvant. In the present work, the appearance of this naloxone sensitivity was studied, using a model of inflammatory hyperalgesia with a more rapid onset, namely carrageenin-induced rat paw edema. In these animals, an extremely low dose of naloxone (3 micrograms/kg i.v.), induced a clear antinociceptive effect (as gauged by the vocalisation threshold to paw pressure), which was observed for both the edematous and the contralateral hind-paw. Small and transient 1 h after carrageenin injection, this effect increased progressively 4 h and 24 h later, reaching a level comparable to that observed with morphine 1 mg/kg i.v. in normal rats, at 24 h. Electrophysiological studies performed in parallel, confirmed the behavioural data so that 24 h after the injection of carrageenin, naloxone (3 micrograms/kg i.v.) reduced the VB thalamic neuronal responses elicited by stimulation of the inflamed paw by 50%. Hypothesis concerning the mechanisms of the paradoxical action of naloxone in models of inflammatory hyperalgesia are discussed.

Citations

Jun 1, 1995·Inflammation Research : Official Journal of the European Histamine Research Society ... [et Al.]·L Stanfa, A Dickenson
Jul 3, 1990·European Journal of Pharmacology·J C WillerT De Broucker
Jun 21, 2006·Journal of Addictive Diseases·Paolo MannelliElisabeth J Van Bockstaele
Jan 21, 2014·Homeopathy : the Journal of the Faculty of Homeopathy·Paolo BellaviteAnita Conforti
May 27, 2017·Current Pain and Headache Reports·O J Michael Coppes, Christine N Sang

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