Orexin is a newly discovered peptide which is synthesized exclusively within the lateral hypothalamic area and perifornical area.Lack of orexin neurons causes narcolepsy-cataplexy, which is characterized by excessive daytime sleepiness, premature transitions to REM sleep, and sudden skeletal muscle weakness without impairment of consciousness.However, most studies so far on the pathogenesis of narcolepsy-cataplexy have been limited merely to the role of orexin in sleep-awake cycle, and the function of orexin on motor control has still been little known.In the present study, effect of orexin-A on the medial vestibular nucleus (MVN), which holds a key position in controlling head and eye movements, were investigated.Immunofluorescence histochemical results showed that both orexin 1 receptors (OX1Rs) and orexin 2 receptors (OX2Rs) are presented in the MVN in rats.Using brain slice preparations and whole-cell patch clamp recordings, type-A and type-B MVN neurons were identified according to the shape of their after hyperpolarization action potentials.A dose-dependent increase in neuronal firing rates and an inward current elicited by orexin-A were observed in both type-A and type-B MVN neurons.