ACUTE INTERACTIVE EFFECTS OF MK-801 AND MORPHINE ON CORTICAL EEG AND EEG POWER SPECTRA IN RATS

The interaction between MK-801 and morphine-induced effects on cortica l electroencephalography (EEG) was investigated. Rats were administere d one of five MK-801 doses (IP) prior to morphine (IV). MK-801 dose-de pendently increased morphine-induced global spectral power, duration o f morphine-induced EEG bursts and latency to sleep onset, and decrease d morphine-induced mean frequency, mobility, complexity, and edge freq uency. MK-801 pretreatment shifted the relative distribution of total power to the left. Significant interaction effects were found for all spectral parameters except peak frequency. A second group of rats was administered MK-801 prior to an increasing cumulative morphine dose. M K-801 increased maximal morphine effects on all spectral parameters ex cept peak frequency. The results are in agreement with those of recent analgesia and in vitro studies in spinal neurons, and support observa tions of a synergistic interaction between effects of NMDA antagonism and morphine. These data further suggest that the component of cortica l EEG that is produced by mu-opioid- and NMDA-receptor interactive eff ects may be dominated by an inhibitory effect of morphine on NMDA rece ptor activity.