title: Cross tolerance between morphine and the long-term analgesic reaction to inescapable shock.
abstract: Animals exposed to a variety of stressors display a temporary analgesic reaction. This short-term analgesia has been shown to be reversible by opiate antagonists and cross-tolerant with morphine following some stress conditions, but not following others. It has recently been shown that inescapable shock parameters which produce behavioral '"learned helplessness" effects also produce a short-term analgesic reaction, and that this reaction can be re-aroused by a brief exposure to shock 24 hours later. Further, both the immediate and long-term antinociceptive reaction which follow shocks of this type have been shown to be reversible by opiate antagonists. Here it is shown that the long-term analgesic reaction is completely cross tolerant with morphine. Implications of these results for opioid mediation of learned helplessness and opioid versus nonopioid mediation of stress-induced analgesia are discussed.
mesh_terms: D000818:Animals; D004361:Drug Tolerance; D004597:Electroshock; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D011930:Reaction Time / Q000187:drug effects
chemical_list: D009020:Morphine