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Acute interactive effects of MK-801 and morphine on cortical EEG and EEG power spectra in rats
1Department of Pharmacology and Toxicology, University of Maryland School of Pharmacy, Baltimore 21201.
Abstract:
The interaction between MK-801 and morphine-induced effects on cortical electroencephalography (EEG) was investigated. Rats were administered one of five MK-801 doses (IP) prior to morphine (IV). MK-801 dose-dependently increased morphine-induced global spectral power, duration of morphine-induced EEG bursts and latency to sleep onset, and decreased morphine-induced mean frequency, mobility, complexity, and edge frequency. 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. MK-801 increased maximal morphine effects on all spectral parameters except peak frequency. The results are in agreement with those of recent analgesia and in vitro studies in spinal neurons, and support observations of a synergistic interaction between effects of NMDA antagonism and morphine. These data further suggest that the component of cortical EEG that is produced by mu-opioid- and NMDA-receptor interactive effects may be dominated by an inhibitory effect of morphine on NMDA receptor activity.
Insights
MK-801, an NMDA receptor antagonist, alters morphine
Area of Science:
- Neuroscience
- Pharmacology
- Electrophysiology
Background:
- Investigating the synergistic interaction between NMDA receptor antagonists and opioids.
- Understanding the neurobiological mechanisms underlying opioid effects on cortical activity.
Purpose of the Study:
- To examine the effects of MK-801, an NMDA receptor antagonist, on morphine-induced changes in rat cortical electroencephalography (EEG).
- To elucidate the interaction between NMDA receptor antagonism and mu-opioid receptor activity in the central nervous system.
Main Methods:
- Rats were administered varying doses of MK-801 before morphine administration (intraperitoneal and intravenous).
- Cortical EEG recordings were analyzed for spectral power, burst duration, sleep latency, frequency, mobility, complexity, and edge frequency.
- Dose-response relationships and maximal effects were assessed.
Main Results:
- MK-801 dose-dependently altered morphine's effects on EEG spectral parameters, increasing power and burst duration while decreasing frequency and complexity.
- MK-801 pretreatment shifted EEG power distribution and significantly interacted with morphine's effects on most spectral parameters.
- These findings align with previous analgesia and in vitro studies, supporting a synergistic interaction.
Conclusions:
- MK-801 and morphine exhibit a synergistic interaction on cortical EEG, influencing various spectral characteristics.
- Morphine's effect on NMDA receptor activity may be inhibitory, dominating their combined neurophysiological impact.
- The study provides insights into the complex interplay between opioid and NMDA receptor systems.