HCRTR2 and narcolepsy: Nevertheless, OX2R signaling is hypothesized to be related to arousal functions of the orexin system based on the finding that loss of the OX2R signaling is associated with symptoms of narcolepsy in animals (Lin et al., 1999; Willie et al., 2003; Akanmu and Honda, 2005; Dugovic et al., 2009).