Selective Enhancement of REM Sleep in Male Rats through Activation of Melatonin MT₁ Receptors Located in the Locus...

Sleep disorders affect millions of people around the world and have a high comorbidity with psychiatric disorders. While current hypnotics mostly increase non-rapid eye movement sleep (NREMS), drugs acting selectively on enhancing rapid eye movement sleep (REMS) are lacking. This polysomnographic study in male rats showed that the first-in-class selective melatonin MT₁ receptor partial agonist UCM871 increases the duration of REMS without affecting that of NREMS. The REMS-promoting effects of UCM871 occurred by inhibiting, in a dose-response manner, the firing activity of the locus ceruleus (LC) norepinephrine (NE) neurons, which express MT₁ receptors. The increase of REMS duration and the inhibition of LC-NE neuronal activity by UCM871 were abolished by MT₁ pharmacological antagonism and by an adeno-associated viral (AAV) vector, which selectively knocked down MT₁ receptors in the LC-NE neurons. In conclusion, MT₁ receptor agonism inhibits LC-NE neurons and triggers REMS, thus representing a novel mechanism and target for REMS disorders and/or psychiatric disorders associated with REMS impairments.