Naloxone-induced hypoalgesia: effects of heat, cold and novelty.
Experiment 1 confirmed that pairings of the opioid antagonist naloxone and a heated floor served to induce and then to maintain a conditioned hypoalgesia in rats. Experiments 2a and b demonstrated that this was not specific to some property of the heated floor: pairings of the drug and a cold floor (a) resulted in conditioned hypoalgesia and (b) maintained the hypoalgesia provoked by pairings of the drug with a heated floor. Experiments 3a and 4 showed that pairings of naloxone with the non-heated floor of the apparatus provoked hypoalgesia and provided evidence that this was due to the drug's disruption of a familiarization process. Experiment 3b revealed that pairings of naloxone with the non-heated floor maintained the hypoalgesia induced by pairings of the drug with a heated one. The results were interpreted to mean that naloxone interacts selectively with a stressor so as to maintain or enhance its aversive properties.
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University of New South Wales, Sydney, Australia.
Westbrook
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D000818:Animals; D001143:Arousal / Q000187:drug effects*; D001245:Association Learning / Q000187:drug effects; D001288:Attention / Q000187:drug effects*; D003214:Conditioning, Classical / Q000187:drug effects; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects; D013697:Thermosensing / Q000187:drug effects*
D009270:Naloxone