Increased REM sleep after intra-locus coeruleus nucleus microinjection of melanin-concentrating hormone (MCH) in the rat

• Microinjection of melanin-concentrating hormone into the right LC increased REM sleep time.
• The effect was related to the occurrence of a greater number of REM sleep periods.
• Values corresponding to W, LS and SWS were not significantly modified.
• These results suggest that the LC neurons are influenced by a MCHergic tone.

A study was carried out on the effects of unilateral microinjection of melanin-concentrating hormone (MCH) into the right locus coeruleus (LC) on the sleep–wake cycle in rats prepared for chronic sleep recordings. MCH 200 ng significantly augmented rapid-eye-movement sleep (REMS) time during the first, second and third 2-h of recording. Furthermore, MCH 100 ng induced a significant increase of REMS during the first 2-h period after treatment. The increment of the behavioral state was related to a greater number of REMS episodes.It is suggested that MCH deactivation of noradrenergic neurons located in the LC facilitates the occurrence of REMS.