Effects of Morphine and Naloxone upon the Reactions of Rats to a Heat Stressor

R. F. Westbrook*, J. D. Greeley, C. P. Nabke, A. L. Swinbourne, A. Harvey

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    16 Citations (Scopus)

    Abstract

    Five experiments used rats to examine the conditioned hypoalgesia induced by exposure to a heated floor. Experiments 1 and 2 demonstrated that this hypoalgesia is mediated by non-opioid mechanisms of pain control, as evidenced by insensitivity to the opioid antagonist naloxone and by the absence of cross-tolerance with the opioid agonist morphine. Although non-opioid in nature, the acquisition of conditioned hypoalgesia was facilitated by naloxone and impaired by morphine (Experiments 3 and 4). These effects did not appear to be due to an opioid regulation of pain. (1) Pairing morphine with the heated floor attenuated acquisition in drug-tolerant rats. (2) This attenuation by morphine was removed when naloxone was given after exposure to the heated floor. (3) Conditioning was facilitated when naloxone was given after exposure to the heated floor (Experiment 5). The results were discussed in terms of an opioid regulation of (a) surprise, (b) arousal of an aversive motivational system, and (c) the affective component of pain.

    Original languageEnglish
    Pages (from-to)323-346
    Number of pages24
    JournalQuarterly Journal of Experimental Psychology Section B: Comparative and Physiological Psychology
    Volume43
    Issue number3
    DOIs
    Publication statusPublished - 1 Aug 1991

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