Neuropeptide glutamic acid-isoleucine (NEI) and melanin-concentrating-hormone (MCH) are cleaved from prepro-MCH. The ventrolateral periaqueductal gray (vlPAG) is one of the sites for REM sleep. Microinjection of NEI and MCH into the vlPAG increase REM episodes. NEI and MCH induce REM sleep at least in part through acting on the vlPAG.