title: Morphine analgesia: enhancement by shock-associated cues.
abstract: Recent research has shown that rats exposed to repeated stress display enhanced morphine analgesia. This study examined the possible contribution of classically conditioned analgesia to this effect. First, drug-naive rats exposed to nine daily sessions of stress, each consisting of a single 45-s exposure to footshock, subsequently displayed enhanced analgesic responsiveness to morphine 1 and 10 days after stress (Experiments 1, 2, and 5). This enhancement was also observed in morphine-experienced rats 1 and 8 days after stress (Experiment 1). Second, the effect of footshock stress on morphine analgesia was found to be specific to the environment in which stress was administered (Experiments 2 and 3). Rats tested in the same distinctive environment in which stress was administered displayed enhanced morphine analgesia; rats shocked elsewhere did not differ from nonshocked controls (Experiment 2). Third, conditioned analgesia was found under the same conditions that yielded enhanced morphine analgesia (Experiments 2 and 4). Lastly, both this conditioned analgesia and the acute analgesia elicited by the footshock stressor were found to be attenuated by naloxone (Experiments 5 and 6). These data are consistent with the hypothesis that the enhanced morphine analgesia observed after repeated footshock stress reflects the contribution of an opioid mediated , conditioned analgesia elicited by cues formerly paired with the stressor.
mesh_terms: D000818:Animals; D004597:Electroshock; D008297:Male; D009020:Morphine / Q000627:therapeutic use*; D009270:Naloxone; D010146:Pain / Q000188:drug therapy* / Q000503:physiopathology / Q000523:psychology; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000502:physiology; D013312:Stress, Physiological / Q000503:physiopathology* / Q000523:psychology
chemical_list: D009270:Naloxone; D009020:Morphine