Prior work has shown that the uncontrollable shock procedure used to induce learned helplessness produces a hormonally mediated opioid hypoalgesia. In addition, it sensitizes subjects to becoming hypoalgesic 24 h later upon exposure to mild "reinstating" shock. In the present study, we tested whether another manipulation that elicits a hormonally mediated opioid hypoalgesia, food deprivation, would have a similiar sensitizing effect. Subjects were food deprived for 48 h, and then, 24 h after food was returned, they were exposed to mild shock. We found that previously food deprived subjects exhibited a much stronger hypoalgesia after mild shock. In addition, they exhibited greater vocalization and struggling when shock was applied. Both effects were attenuated by the opiate antagonist naltrexone. In contrast to past results, only a weak hypoalgesia was observed in the saline-treated nondeprived subjects. Experiment 2 showed that this was due to our having tested subjects during the early portion of the light cycle.
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