Delta opiate receptors are involved in the endopioid-induced myoclonic contractions

Abstract

Morphine, the prototype mu opiate receptor agonist, decreased the spontaneous and [D-Ala 2]-Met-enkephalinamide (DALA)-induced myoclonic contractions (MC) of submandibular muscles in the anaesthetized rat. The proposed kappa receptor agonists ketocyclazocine, ethylketocyclazocine and bremazocine failed to induce MC. In addition, bremazocine inhibited the spontaneous and DALA induced MC. Cy-clazocine, the so-called sigma opiate receptor agonist, had a weak potency in generation of MC, but without step dose response tendency. The most potent opioid peptide in inducing the MC and electrocortical (ECoG) epileptic pattern was the delta opiate receptor agonist [D-Ala 2,D-Leu 5]-enkephalin (DADL). All drugs were administered intraventricularly. The results indicate that myoclonic phenomena induced by DADL and probably by other endopioids are mediated by delta opiate receptors in the rat brain. It is suggested that the combined ECoG and EMG method used in this study offers an opportunity to define further the biological role of opiate receptors and to identify the potential delta opiate receptor acting drugs, which might provide a new approach to the therapy of some seizure disorders.