Effect of dermorphin on behavior and hippocampal electrical activity in rabbits

Dermorphin, a naturally occurring heptapeptide that selectively binds to mu-opioid receptors, was injected intravenously 0.4 mg/kg in male rabbits. Eight days before injection the spontaneous behavior of the animals was observed in a neutral environment in the absence of external stimuli. At the same time, hippocampal EEG was recorded by telemetry. After dermorphin injection, the same experimental procedure was repeated. Behavior showed a strong increase in quiet immobility and a concomitant reduction in voluntary activities as compared to control periods. Treatment did not affect either the pattern or the frequency of hippocampal electrical activity.