PREVIOUSLY FOOD DEPRIVED RATS EXHIBIT AN EXAGGERATED MORPHINE ANALGESIA. M.K. Biles*, P.A. Illich, and J.W. Grau. Dept. of Psychology , Texas A&M University, College Station, TX 77843.
Previous research has shown that an extended exposure to inescapable shock elicits a strong hormonally mediated opioid analgesia. In addition, it sensitizes the opioid system to being reactivated, 24 hrs later, upon exposure to a low dose of morphine (1 mg/kg) (Grau et al., Science, 203:1409, 1981). Here we determined whether another manipulation which elicits a hormonally mediated opioid analgesia, food deprivation (Hamm et al., Physiol. & Beh., 35: 879, 1985), has a similar sensitizing effect.
Subjects had their food removed and after 24 hrs were given 9g of food. After an additional 24 hrs, food was returned. Twenty-four hours after food was returned, subjects were injected with 1 mg/kg morphine or saline. Pain reactivity was assessed 30 min later with the tail-flick test. WE found that morphine elicited a much stronger analgesia in previously food deprived subjects. In a second experiment, we assessed pain reactivity over a 3 hr period following the injection. We found that previously food deprived subjects exhibited an exaggerated morphine analgesia for the entire 3 hrs of testing. Oddly, the saline controls exhibited the opposite pattern; previously food deprived subjects were hyperalgesic relative to non-deprived controls. Supported by NSF grant BNS 8819981.
Published in Society for Neuroscience Abstracts, 15, 1989.