Endogenous noradrenergic tone controls symptoms of allodynia in the spinalnerve ligation model of neuropathic pain

Endogenous inhibitory controls were studied in the spinal nerve ligation mo del of neuropathic pain. Atipamezole, a selective alpha(2)-adrenoceptor ant agonist, produced both mechanical and cold allodynia in those rats which ha d not developed clear neuropathic symptoms, The same doses (50 mu g i.t, or 1 mg/kg s.c.) did not increase the severity of symptoms in rats which had developed them. The opioid receptor antagonist naloxone (20 mu g i.t. or 1 mg/kg s.c.) had no effect on the neuropathic symptoms. These results indica te that mechanical and cold allodynia are under endogenous noradrenergic ra ther than opioidergic control in this model of neuropathic pain. (C) 1999 E lsevier Science B.V. All rights reserved.