Behavioral and electrocortical effects of beta-endorphin after intracerebral infusion in rats

In rats with cannulae chronically implanted into specific areas of the brain, the effects of beta-endorphin were studied on behavior and electrocortical activity. It has been shown that analgesia and catatonia were evoked after infusing beta-endorphin into the III cerebral ventricle or into the hypothalamus. On the contrary, beta-endorphin microinjected into the caudate nucleus or into the substantia nigra produced an intense pattern of stereotyped movements, occasional contralateral circling, contralateral myoclonic jerks and asymmetric posture. Stereotyped gnawing, grooming and "wet-dog" syndrome preceded catatonia after intrahypothalamic administration of beta-endorphin. Bilateral (III ventricle) or ipsilateral (hypothalamus, caudate nucleus and substantia nigra) high voltage electrocortical spikes and other ECoG pathological changes accompanied by motor disorders (stereotypies, myoclonic jerks) or without any overt behavioral change were constantly observed. Behavioral and electrocortical changes evoked by beta-endorphin were long-lasting and rapidly reversed by the specific opiate antagonist, naloxone.