Assessment of hypnotic effects in the rat: Influence of the sleep‐awake cycle

Abstract The influence of the sleep‐awake cycle of the rat on the apparent hypnotic effects of two benzodiazepine hypnotics, triazolam (short half‐life) and flurazepam (long half‐life), was assessed. Cortical electroencephalographic recordings from freely moving animals were used to determine whether the rats were awake or asleep. When tested during the dark phase of the light‐dark cycle, when rats sleep approximately 50% of each hour, both agents increased sleep, with flurazepam having a longer duration of action than triazolam. In contrast, when tested during the light phase of the light‐dark cycle, when rats sleep approximately 70–90% of each hour, the sleep‐inducing effects of the two agents could not be distinguished. These data emphasize the importance of baseline levels of sleep in assessing hypnotic‐drug effects.