Differential effects of scopolamine on nocturnal cortisol secretion, sleep architecture, and REM latency in normal volunteers: Relation to sleep and cortisol abnormalities in depression

Scopolamine (SCOP) (3.0 μ/kg and 6.0 μg/kg) and saline were administered intramuscularly at 11:00 pm to eight normal male volunteers in a randomized design, and the effects on the sleep electroencephalogram (EEG) and nocturnal cortisol secretion (via blood sampling every 15 min) were evaluated. Compared to saline, SCOP produced a significant dose-related delay in rapid eye movement (REM) latency. In contrast, neither dose of SCOP significantly affected nocturnal plasma cortisol concentrations. These results suggest that the central cholinergic system that regulates the onset of REM sleep is more sensitive to dysregulation than the cholinergic system that controls the degree of nocturnal cortisol secretion. If central cholinergic overactivity is responsible for both the REM sleep latency and cortisol abnormalities in depressed patients, then our findings with SCOP might help explain why the incidences of these abnormalities are different.