beta-Endorphin-induced psychomotor excitation in the cat

The effect on behavior of synthetic human beta-Endorphin injected into the cerebral ventricles of the cat was investigated in these experiments. beta-endorphin produced psychomotor excitation (i.e., restlessness, apprehension, flight and locomotion), accompanied by pupillary dilatation and tremor. Between periods of locomotion, the cat sat moving its head from side to side with eyes wide open and mydriasis, or stood stiffly with a vacant stare, pupils dilated and eyes wide open. During this time the cat did not react to objects moving in front of it. Behavioral changes produced by a single dose of beta-endorphin were dose-dependent and long-lasting. Pretreatment with intracerebroventricular nalorphine depressed or abolished the behavioral changes, mydriasis and tremor caused by beta-endorphin. It is concluded that beta-endorphin acts on central opiate receptors promoting psychomotor excitation.