REM sleep and cortisol response to the cholinergic challenge with RS 86 in normals and depressives

The influence of the muscarinic agonist RS 86 on rapid-eye-movement (REM) sleep and on hypothalamic-pituitary-adrenocortical (HPA) axis was studied in healthy subjects and in patients with a major depression. In both groups, RS 86 induced a shortening of REM latency and an increase in REM sleep; these effects were more pronounced in the depressives than in the controls. This finding supports the assumption that in depression the REM sleep regulating neurons are hypersensitive to cholinergic stimuli. However, neither in the healthy subjects nor in the depressed patients was an RS 86 induced increase in plasma cortisol seen. This observation does not agree with the assumption that, in humans, the HPA axis is stimulated by muscarinic neurons and that hypercortisolemia in depression is due to an overactivity of muscarinic neurons activating the HPA axis.