The ‘tonic’ pain-related behaviour seen in mononeuropathic rats is modulated by morphine and naloxone

• Published in: Pain (Amsterdam) Vol. 44; no. 1; pp. 97 - 102
• Main Authors: Jazat, F., Guilbaud, G.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 1991; Elsevier
• Subjects: Analgesics; Animals; Behavior, Animal - drug effects; Biological and medical sciences; Dose-Response Relationship, Drug; Male; Medical sciences; Morphine - pharmacology; Naloxone; Naloxone - pharmacology; Nervous System Diseases - psychology; Neuropathy; Neuropharmacology; Opioids; Pain - psychology; Pain Measurement; Pharmacology. Drug treatments; Rat; Rats; Rats, Inbred Strains; Sciatic Nerve - physiology; Tonic pain; Tonic pain; Naloxone; Neuropathy; Rat; Opioids; Nervous system diseases; Evaluation scale; Rodentia; Morphine; Opiates; Peripheral neuropathy; Vertebrata; Experimental disease; Mammalia; Pain; Ligature; Investigation method; Animal; Behavior; Sciatic nerve
• ISSN: 0304-3959; 1872-6623
• DOI: 10.1016/0304-3959(91)90154-P

This study investigated the sensitivity to pharmacological manipulations of a rating method, adapted from the formalin test, to measure the tonic component of the pain-related behaviour induced by creating a peripheral mononeuropathy with 4 loose ligatures around the common sciatic nerve. Although the adequacy of opioid substances in alleviating neuropathic pain is highly controversial, the effects of morphine (1 mg/kg i.v.) and naloxone (1 mg/and 3 μg/kg i.v.) were tested 1–2 weeks after the nerve ligatures were established, when pain-related behaviours were well developed. Morphine (1 mg/kg i.v.) induced a potent and prolonged decrease in the pain-rating score at week 2 after surgery. Either at week 1 or week 2, naloxone elicited a bidirectional dose-dependent action: a further increase in the pain-rating score with the high dose (1 mg/kg i.v.), and a paradoxical decrease in the score with the low dose of 3 μg/kg i.v. These effects are comparable to those already described in several rat models of inflammatory pain and, in the same model of neuropathy, using a phasic nociceptive test, the measure of the vocalization to paw pressure. A few differences in the effects of naloxone on tonic and phasic pain are noted and discussed.