Interaction of stress and morphine in the rat using a classical conditioning design

Abstract

Previous studies have suggested that aversive and stressful stimulation may affect endogenous opioid systems and produce physiological changes (e.g., analgesia, Straub tail response) typically associated with opiate stimulation. The present experiment addressed the effect of stressful but not immediately painful stimulation upon an opiate-mediated syndrome using a novel procedure. Noise stress and morphine administration were factorially varied in the classical conditioning of environmental preference in a two-choice apparatus. In comparison with control subjects which showed no change, morphine produced a preference shift toward the conditioned environment which was further potentiated by a noise stimulation. Thus, stress may potentiate the reinforcing effects of opiate alkaloids.