Figure 1.

The effects of intraperitoneally (i.p.) administered single doses of tramadol (5, 15 and 45 mg/kg) or vehicle on the amount of (a) wakefulness, (b) non-rapid eye movement (NREM) sleep and (c) rapid eye movement (REM) sleep for 10 h after the injections. The arrows show the time of the administration, at the beginning of the passive phase. At this time point, all animals were awake. The mean value of the first hour is connected with time zero by dashed lines. The &, # and * signs represent significant results (p < 0.05) of the post hoc tests, compared to vehicle in the case of the 5, 15 and 45 mg/kg tramadol-treated groups, respectively. Data are presented as mean ± SEM of n = 8 rats/group.