The specific role that hypocretin plays in narcolepsy described in the DSM-V (Diagnostic and Statistical Manual of Mental Disorders, fifth edition), as a disorder in which the individual will experience recurrent periods of an irresistible need to sleep, has now been established, both in preclinical models and through human studies (Chemelli et al., 1999; Lin et al., 1999; Nishino et al., 2000; Thannickal et al., 2000; Ripley et al., 2001). Here, HCRT is linked to narcolepsy.