title: Involvement of endogenous opioids with forced swimming-induced immobility in mice.
abstract: The present study investigated the involvement of endogenous opioid mechanisms with the immobility response induced in mice by forced swimming. Pretreatment with the narcotic antagonist naloxone (0.625--40.0 mg/kg) caused a dose-dependent decrease in the duration of immobility in mice subjected to a 10 min swim test. This effect was more pronounced in C57BL/6J mice than in BALB/C mice. A low dose of morphine (0.15 mg/kg) potentiated immobility whereas higher doses (0.625/10.0 mg/kg) had no demonstrable effect on immobility in these strains. The results suggest that release of endogenous opioids may be a physiological event promoting natural cataleptic-like behaviors in mice.
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004723:Endorphins / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009020:Morphine / Q000494:pharmacology; D009043:Motor Activity / Q000502:physiology*; D009270:Naloxone / Q000494:pharmacology; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology; D013550:Swimming
chemical_list: D004723:Endorphins; D011957:Receptors, Opioid; D009270:Naloxone; D009020:Morphine