EEG, EEG power spectral, and behavioral differences in response to acute ethylketocyclazocine administration in two inbred rat strains.

Differences in response to behavioral and electroencephalographic parameters were delineated between two inbred rat strains, Lewis (LEW) and Fischer 344 (F344), upon acute exposure to IV administration of ethylketocyclazocine (EKC) at doses of 1.25, 2.5, and 5 mg/kg. Duration of EKC-induced EEG slow-wave bursts and associated behavioral stupor increased in a dose-related manner, and was greater in duration for the LEW animals; a less robust, quadratic trend was displayed by the F344 group. For both rat strains, latency to onset of slow-wave sleep increased proportionately with EKC dose. Duration of EKC-induced EEG bursts and interbursts were greater in duration for the F344 rats. Assessment of six power spectral parameters (peak frequency, complexity, mobility, mean frequency, edge frequency, and total power) revealed no differences between groups when EKC-induced burst and interburst periods were analyzed simultaneously. Separation of the phases revealed rat strain differences; overall, the LEW animals displayed a greater dose-related EEG response. Except for total power, the F344 group displayed little variation across the three doses tested in the burst phase; the interburst phase reflected more dose-related differences for this group but to a lesser degree than the LEW animals. These results may reflect differences in opioid-related receptor populations between Lewis and F344 inbred rat strains.