Differential effects of nitric oxide synthase inhibitor, 7-nitroindazole, on discriminative stimulus and somatic effects of naloxone in morphine-dependent rats

Our previous report suggested that antagonists acting at NMDA receptors att enuate discriminative stimulus effects of naloxone in morphine dependent ra ts. Nitric oxide (NO) is a putative second messenger which mediates NMDA re ceptor activation. The present study evaluated behavioral effects of NO syn thase inhibitor, 7-nitroindazole in morphine-dependent rats trained to disc riminate 0.1 mg/kg naloxone from saline. 7-Nitroindazole did not significan tly affect naloxone's discriminative stimulus effects but decreased naloxon e-induced weight loss and abolished expression of several withdrawal signs - diarrhea, scream on touch, tremor and 'wet dog'-like shaking suggesting d ifferent mechanisms for subjective and somatic components of opioid withdra wal. (C) 1999 Elsevier Science B.V. All rights reserved.