Differential epileptogenic potentials of selective? and? opiate receptor agonists

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Abstract
By using electroencephalographic (EEG) and electromyographic recordings in anaesthetized and free-moving rats, two opioid peptides, known as selective agonists forμ andδ opiate receptors, respectively, were examined for their epileptogenic properties. Theδ receptor peptide (DSTLE, 4.6–18.6 nmol, intraventricularly, ivt), a putativeδ opiate agonist, produced a dose-related increase of myoclonic contractions (MC) with epileptic discharges in anaesthetized rats and severe wet dog shakes, with occasionally falling down, in free-moving animals. Morphiceptin, a specificμ opiate agonist, used in equimolar doses and under the same experimental conditions, had a significantly less pronounced effect on the number of MC and epileptiform EEG phenomena. Similarly, DSTLE (18.6 nmol) injected in the CA2 area of the hippocampus, a region with a nearly equal distribution ofμ andδ opiate receptors, induced epileptic discharges in anaesthetized and free-moving rats, while an equimolar dose of morphiceptin had no significant effect. It is suggested that the epileptiform activity of opioid peptides is mainly due to an activation ofδ opiate receptors in the central nervous system.