CONDITIONED FEAR EXACERBATES ACUTE MORPHINE-DEPENDENCE

A variety of physical stressors have been shown to enhance reactivity to opioid drugs. Few studies have examined the effects of nonphysical stressors on opioid drug reactivity. In this regard, it has previously been shown that animals administered morphine in the presence of shoc k-associated cues demonstrate increases in hypoalgesia relative to non shock control animals. These findings have typically been viewed as be ing mediated by the activation of endogenous pain inhibition systems v ia conditioned fear. In this series, we further examined the nature of these effects by assessing the effects of conditioned fear on acute m orphine dependence. Experiment 1 revealed that animals administered 3 mg/kg morphine in the presence of context fear cues demonstrated an en hanced withdrawal response when removed and administered 3 mg/kg nalox one. Because it is known that conditioning effects do not diminish ove r time, a second experiment examined whether the enhancement of acute dependence by context fear would still be evident 72 h postconditionin g. As in Experiment 1, animals administered morphine in a context asso ciated with shock demonstrated an enhancement of acute dependence. Exp eriment 2b revealed that the shock parameters used in these studies ca n induce a hypoalgesic response on the test that is opioid mediated. T hese findings are discussed with regard to the neuroanatomy of fear sy stems as they relate to the neuropharmacological study of opioid withd rawal.