MORPHINE POTENTIATION OF TONIC IMMOBILITY - EFFECTS OF NALOXONE, PCPA, AND 5,6-DHT

The duration of tonic immobility in chickens, a catatonic-like state produced by brief restraint, was greatly potentiated by a single 1.0 mg/kg injection of morphine. Naloxone by itself, however, had no effect on tonic immobility, and only an exceptionally large dose of naloxone blocked the morphine potentiation. Pretreatment with PCPA and 5,6-dihydroxytryptamine completely eliminated the morphine enhancement. The effect of morphine on tonic immobility may be mediated by a central serotonergic-raphe system. © 1979.