Interactive effects of MK-801 and morphine on EEG, EEG power spectra and behavior in rats: II. Morphine dependence.

A potential interaction between MK-801 and the cortical electroencephalographic (EEG) and behavioral expressions of morphine dependence in female Sprague-Dawley rats was assessed. Rats were treated chronically (7 days) with either morphine alone, morphine and MK-801, MK-801 alone or saline vehicle alone. On day 8 all rats received morphine alone followed by naloxone. An additional group received chronic (7 days) morphine alone, followed by MK-801 on day 8 prior to morphine and naloxone. Naloxone-induced EEG complexity in morphine-dependent rats was significantly lower than in chronic saline-treated rats. Total power, mobility, mean frequency, complexity and edge frequency in response to naloxone-induced withdrawal in morphine-dependent rats were significantly altered from those in chronically MK-801 alone-treated rats. No differences were found in the EEG and behavioral responses to naloxone between rats that received chronic MK-801 and those that didn't during chronic morphine treatment. Acute MK-801 prior to naloxone in morphine-dependent rats attenuated the behavioral, but not the EEG response to naloxone-induced withdrawal.