Genetic profiles of morphine-induced EEG, EEG power spectra, and behavior in two inbred rat strains.

The purpose of the present study was to examine and compare the effects of morphine at doses of 3, 10, and 30 mg/kg, IV, on EEG, EEG power spectra, and behavior in two inbred rat strains, Lewis and Fischer 344. Duration of morphine-induced EEG slow-wave bursts and associated behavioral stupor was greater in Lewis rats. Latency to slow-wave sleep increased in a dose-related manner for both strains; differences were not significant between the two groups. The analog EEG signal was transformed by fast Fourier analysis; six power spectral quantities were examined: peak frequency, complexity, mobility, mean frequency, edge frequency, and total power. With the exception of peak frequency and edge frequency, all differed as a function of inbred rat strain. Regarding morphine dose, all spectral parameters differed except peak frequency. Factor analysis on morphine-induced EEG revealed a unique factor for each strain that was bipolar in nature and may be associated with the burst and interburst periods that occur in EEG after opiate administration. Genetic variability appears to play a role in the behavioral, EEG, and derived power spectral responses of both LEW and F344 inbred rat strains following acute morphine administration. These results may reflect differences in neurosensitivity and/or opioid receptor populations between Lewis and Fischer 344 inbred rat strains.