A PERIOD OF RESTRAINT IS NECESSARY TO OBSERVE A STRONG OPIOID ANALGESIA AFTER MILD SHOCK OR A LOW-DOSE OF MORPHINE IN RATS. M.K. Biles & J.W. Grau. Dept. of Psychology, Texas A&M Univ., College Station, TX 77843.

We have previously shown that exposure to mild shock (3, 0.75-s, 1.0 mA tail-shocks) can elicit both a transient nonopioid and a long-lasting opioid analgesia on the tail-flick test. Unlike the analgesia observed after other "brief shock" paradigms, the analgesia observed in our paradigm appears to be hormonally mediated since it is attenuated by adrenalectomy and dexamethasone (Biles et al., (Neurosci. Abs., 16), 99, 1990). We hypothesized that the pituitary-adrenal axis may play a role in our paradigm because subjects are restrained for 20 min before they receive mild shock. The present experiments test this hypothesis. Experiment 1 showed that removing this 20 min period of restraint attenuated the opioid analgesia normally observed 6-10 min after mild shock. Experiment 2 demonstrated that this period of restraint has relatively little impact on the naltrexone-insensitive, nonopioid, analgesia observed 2 min after shock. The last experiment showed that the 20 min of restraint also potentiates the analgesia observed after a low dose (1 mg/kg) of morphine. The results suggest that a period of restraint acts to potentiate opioid mediated analgesic effects. Supported by a Tex. Adv. Res. Proj. (010366-097) to J.W.G.

Published in Society for Neuroscience Abstracts, 17, 1991.

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