Orexin neurons send excitatory innervation to serotonergic neurons in the raphe nuclei, which abundantly express both OX1R and OX2R (Brown et al., 2002; Liu et al., 2002; Kohlmeier et al., 2013), suggesting that activity of serotonergic neurons is partly regulated by orexin neurons, and this function was shown to be important for inhibition of cataplexy in narcoleptic mice (Mieda et al., 2011; Hasegawa et al., 2017). Here, HCRTR2 is linked to Cataplexy.