HCRT and narcolepsy: At the time, narcolepsy had no known cause and as such, this observation led to the rapid uptake of research into the orexin system’s role in the regulation of sleep (Lin et al., 1999; Scammell et al., 2000; Estabrooke et al., 2001; Saper et al., 2001; Sakurai, 2007; Tsujino and Sakurai, 2009).