Figure 1.

Representative 12 h dark period (20:00 hours to 08:00 hours) hypnograms for wild type mice (WT), H₁R^−/− mice, H₁R^−/−; OX₁R^−/− mice and OX₁R^−/−;OX₂R^−/− mice. The height of the horizontal line above baseline indicates the vigilance state of the mouse at the time. W, wakefulness; NR, non-rapid eye movement (REM) sleep; R, REM sleep. There were no significant differences in sleep/wake phenotypes between wild type mice, H₁R^−/− mice, and H₁R^−/−;OX₁R^−/− mice. In contrast, OX₁R^−/−;OX₂R^−/− mice showed severe fragmentation of sleep/wake states, along with frequent direct transitions from wakefulness to REM sleep (mark with arrowhead). Hypnograms were obtained by simultaneous EEG/EMG recording as described previously (Chemelli et al. 1999).