HCRTR2 and narcolepsy: Mice lacking the OX2R receptor have narcolepsy manifestations, whereas knockout OX1Rmice show only mild sleep disturbances[36]; however, the sleep wake cycle defect in the knockout dual recipient mice is more severe than in the knockout OX2R only mice.[37] Thus, it could be shown that both OX1R and OX2R are essential for the maintenance of wakefulness, with the role of OX2R being more important.