Single administration of metyrapone modifies sleep–wake patterns in the rat

Metyrapone is a glucocorticoid synthesis inhibitor largely used to study glucocorticoid involvement in stress and memory processes. Metyrapone also acts as a stressor and therefore might modify sleep/wake patterns. However, its effects on rat sleep are unknown. We equipped 8 rats for telemetric assessment of EEG and EMG. They received first a saline injection and 2 days later a 150 mg/kg metyrapone injection. Metyrapone provoked immediately a waking effect together with a 3-h decrease in slow-wave sleep (SWS) and a 5-h decrease in rapid eye movement sleep (REM sleep). Thereafter, the rats exhibited homeostatic compensation through SWS and REM sleep rebounds recovering totally the sleep debt. The finding that metyrapone modified sleep patterns is important to consider for stress and memory studies using metyrapone.