Opioids cause dissociated states of consciousness in C57BL/6J mice.

Abstract

The electroencephalogram (EEG) provides an objective, neural correlate of consciousness. Opioid receptors modulate mammalian neuronal excitability, and this fact was used to characterize how opioids administered to mice alter EEG power and states of consciousness. The present study tested the hypothesis that antinociceptive doses of fentanyl, morphine, or buprenorphine differentially alter the EEG and states of sleep and wakefulness in adult, male C57BL/6J mice. Mice were anesthetized and implanted with telemeters that enabled wireless recordings of cortical EEG and electromyogram (EMG). After surgical recovery, EEG and EMG were used to objectively score states of consciousness as wakefulness, rapid eye movement (REM) sleep, or non-REM (NREM) sleep. Measures of EEG power (dB) were quantified as δ (0.5-4 Hz), θ (4-8 Hz), α (8-13 Hz), σ (12-15 Hz), β (13-30 Hz), and γ (30-60 Hz). Compared with saline (control), fentanyl and morphine decreased NREM sleep, morphine eliminated REM sleep, and buprenorphine eliminated NREM sleep and REM sleep. Opioids significantly and differentially disrupted the temporal organization of sleep/wake states, altered specific EEG frequency bands, and caused dissociated states of consciousness. The results are discussed relative to the fact that opioids, pain, and sleep modulate interacting states of consciousness.NEW & NOTEWORTHY This study discovered that antinociceptive doses of fentanyl, morphine, and buprenorphine significantly and differentially disrupt EEG-defined states of consciousness in C57BL/6J mice. These data are noteworthy because: 1) buprenorphine is commonly used in medication-assisted therapy for opioid addiction, and 2) there is evidence that disordered sleep can promote addiction relapse. The results contribute to community phenotyping efforts by making publicly available all descriptive and inferential statistics from this study (Supplemental Tables S1-S8).