Alteration in the sleep-wakefulness patterns by benzodiazepines in the cat

Abstract

Qualitative and quantitative alterations of sleep and wakefulness patterns induced by diazepam and nitrazepam (0.25–2 mg/kg intramuscularly) have been studied in two cats. Polygraphic recording started between 1 and 2 p.m., following injection of normal saline (control experiment) or of the diazepine under study, and was carried out continuously for 24 h. Twenty-five recordings were performed over a 6 month period for each animal. Control experiments alternated with drug studies. 1. 1. With diazepam and low doses of nitrazepam the EEG was characterized by increased amplitude of the fast activity, seen mainly in the anterior regions and the hippocampus. The spindles of drowsiness and sleep were then replaced by high voltage fast activity which occurred at times in bursts. With large doses of nitrazepam (from 0.75 mg/kg), high voltage spindles might still occur but at a much higher frequency than 8 c/sec. 2. 2. In spite of causing a marked drop in muscle tone these two diazepines induced a long period of restlessness; the number and duration of wakeful periods therefore increased at the expense of all sheep stages and especially of rapid eye movement (REM) sleep. 3. 3. REM sleep was almost completely eliminated by diazepam and nitrazepam for 6–18 h, according to the dose. The manifestations of this stage, when they did occur, were very short and characterized by total disappearance of eye movements in spite of persistance of phasic activity in the visual cortex. 4. 4. The number of complete and incomplete sleep cycles over a 24 h recording period was distinctly reduced by both drugs. 5. 5. During a given experiment all the EEG and behavioral changes evolved contemporaneously and became normal again at the same time. 6. 6. For equal doses nitrazepam is more potent and the effect lasts longer than with diazepam.