Morphine catalepsy as an adaptive reflex state in rats.

A series of experiments with 56 male Long-Evans rats demonstrated that catalepsy induced by morphine sulfate (20–80 mg/kg, ip) consists of 2 complementary, but opposite, behavioral extremes (rigid immobility and sudden locomotor bursts), each of which could be controlled by distinct classes of external stimuli. When stimuli that involved pain and/or nonnociceptive skin pressure were tonic (continuous), morphine-induced EEG deactivation and behavioral immobility were potentiated, even to the extent that a stimulation-bound reversible coma resulted. In contrast, phasic (discrete stimulation produced behavioral and/or EEG activation. EEG and behavioral rebound effects were observed following stressful (intense, prolonged) stimuli. On the basis of the observed stimulus controls, sensorimotor characteristics, and EEG reactions, it is suggested that similarities may exist between morphine-induced catalepsy and defensive reactions of immobility and escape in drug-free animals (i.e., the adaptive death-feigning reflex). (59 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)