ELECTROENCEPHALOGRAPHIC AND BEHAVIORAL-EFFECTS OF D-ALA2-METHIONINE-ENKEPHALINAMIDE AND MORPHINE IN RAT

  • 1 January 1978
    • journal article
    • research article
    • Vol. 206  (3) , 636-643
Abstract
Rats were prepared with chronic cortical and temporalis muscle electrodes and bilateral intraventricular (i.vt.) cannulae. The direct and voltage integrated EEG and integrated electromyogram and gross behavior were monitored after the i.vt. injection of D-enkephalin (10-240 .mu.g), morphine (2.5-40 .mu.g), naloxone (25-50 .mu.g) or sterile H2O (10 .mu.l). EEG high-amplitude slow-frequency waves (EEG slow bursts) occurred after i.vt. morphine or D-enkephalin and were associated with behavioral stupor. The behavioral depressant effect was followed by behavioral arousal and EEG activation. The EEG voltage output during morphine or D-enkephalin-induced EEG slow-wave activity was dose-dependent and was correlated with the behavioral state of the rat. D-Enkephalin was less potent and shorter-acting than morphine but produced a greater maximal response with respect to increasing the EEG voltage output. The effects of D-enkephalin and morphine were antagonized by pretreatment with naloxone (10 mg/kg s.c.). The i.vt. injection of naloxone alone or sterile H2O had no disruptive effect on the EEG or behavior of the rat. A dose-response relationship for the i.vt. administration of morphine and D-enkephalin was established. The difference in maximal EEG response between morphine and D-enkephalin supports the contention that heterogenous opiate receptors in the brain may mediate their effects.