Cholinergic REM induction test: muscarinic supersensitivity underlies polysomnographic findings in both depression and schizophrenia.

Disinhibition of rapid eye movement (REM) sleep (e.g. shortening of REM latency, heightened REM density) is frequently encountered in patients with a major depressive disorder (MDD). Administration of cholinomimetics prior to or during sleep leads to a more pronounced advance of REM sleep in depressed patients compared to healthy controls and patients with other psychiatric disorders. The present study tested whether the cholinergic REM induction test (CRIT) with 1.5 mg RS 86 (an orally acting muscarinic agonist) differentiates patients with MDD (n = 40) from those with schizophrenia (n = 43) and healthy controls (n = 36). The most pronounced shortening of REM latency after cholinergic stimulation occurred in patients with MDD. However, a significant number of patients with schizophrenia also displayed short REM latencies (REM latency < 25 minutes) under placebo conditions and after cholinergic stimulation. REM density measures more clearly differentiated patients with MDD from those with schizophrenia. It is concluded that a subgroup of patients suffering from schizophrenia displays signs of a muscarinic receptor supersensitivity.