Selective Enhancement of REM Sleep in Male Rats through Activation of Melatonin MT1Receptors Located in the Locus Ceruleus Norepinephrine Neurons

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 MT 1 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 MT 1 receptors. The increase of REMS duration and the inhibition of LC-NE neuronal activity by UCM871 were abolished by MT 1 pharmacological antagonism and by an adeno-associated viral (AAV) vector, which selectively knocked down MT 1 receptors in the LC-NE neurons. In conclusion, MT 1 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.