Differential electrographic patterns for specific mu- and delta-opioid peptides in rats

Cortical electroencephalographic (EEG) recordings were performed on rats after i.v. administration of morphine and specific mu- and delta-opioid peptides. DAGO (Tyr-D X Ala-Gly-N X Me X Phe-Gly-ol), the mu-selective peptide, produced repetitive paroxysmal discharges organized in a pattern analogous to that seen in tonic clonic seizures at doses which produced analgesia while DTLET (Tyr-D X Thr-Gly-Phe-Leu-Thr), the delta-selective peptide, produced 'petit-mal'-like seizures at doses which caused neither analgesia nor catatonia. It is suggested that the delta receptor is preferentially implicated in the epileptogenic spectrum of opioids.