OPIATE WITHDRAWAL-LIKE BEHAVIOR INDUCED BY NALOXONE FOLLOWING EXPOSURE TO A CONTEXTUAL FEAR STIMULUS

1. Considerable experimental attention has been directed at understand ing the role of opioid peptides in mediating stress effects. Fewer stu dies have utilized non-physical or 'psychological' methods to investig ate the role of the opioid system in stress. 2. Recent studies have sh own that conditioned fear, a psychological stressor, can augment morph ine induced analgesia and acute dependence. Two experiments were condu cted to assess withdrawal-like behavioral changes induced by the gener al opioid antagonist naloxone, in the absence of morphine, following e xposure to a context conditioned fear stimulus. 3. Experiment 1 demons trated that a high dose of naloxone (10 mg/kg) produced a specific inc rease in one behavioral index of negative affect, forepaw tremor behav ior, in rats exposed to a context fear stimulus. 4. Experiment 2 asses sed the relative effects of several naloxone (0, 1, 5, 10 mg/kg) doses in inducing withdrawal-like behavioral changes in animals exposed to a conditioned fear context. This experiment revealed that low doses of naloxone produced an overall increase in all behaviors. High naloxone doses tended to increase only forepaw tremor behavior. 5. The results are discussed ih terms of opioid systems and stress.