The acute effects of reserpine on the sleep-wakefulness cycle in rabbits

Summary The acute effects of reserpine on the sleep-wakefulness cycle were systematically studied in five male rabbits with chronically implanted electrodes for recording the EEG, the EMG of the neck muscles, and the oculogram. After careful control studies during which the rabbits became accustomed to the experimental situation and attained stable sleep-wakefulness patterns, various doses of reserpine (1.0, 0.5, 0.25, 0.1, 0.05 mg/kg) were injected intravenously and 5-hr polygraphic recordings were made. Twenty-four hours after administration, 2-hr recordings were made for all doses studied; for the dose of 1.0 mg/kg 2-hr recordings were also made 48 hours after administration. The percent times of the three stages, alert, slow wave sleep and paradoxical sleep, were calculated for the total recording time. In the unmedicated animals the percentages during 2-hr recordings were: alert, 32.9±5.7; slow wave sleep, 61.5±5.9; and paradoxical sleep, 5.6±1.1. Paradoxical sleep was also calculated for the first hour and the remaining 4 hours of the 5-hr recording period both as to percent time and the duration of single episodes. Some behavioral and polygraphic characteristics of paradoxical sleep were described. Reserpine, in doses of 1.0 to 0.25 mg/kg, caused a biphasic response; an initial alert period of 1 1/2 to 2 hours followed by a slow-wave-sleep period which endured until the end of the 5-hr recording. Suppression of paradoxical sleep was observed with doses of 1.0 to 0.1 mg/kg, although the doses of 0.25 and 0.1 mg/kg did not suppress it during the first hour after injection. The percent time of paradoxical sleep in total recording time showed a dose-dependent decrease: 0.2% for 1.0 mg/kg, 0.1% for 0.5 mg/kg, (both significant,p<0.001), 0.6% for 0.25 mg/kg (p<0.01), 2.4% for 0.1 mg/kg (p<0.05), 3.5% for 0.05 mg/kg (not significant) and 5.1% for the saline control. The duration of single episodes of paradoxical sleep was not changed by reserpine. In the 2-hr recordings made one and two days after reserpine administration the percent time of paradoxical sleep did not differ significantly from the normal level.