抄録
Although the accumulated evidences show orexin plays important roles in the narcolepsy, there are few reports indicating the orexinergic regulation on the neurotransmitters' releases related to the symptoms of narcolepsy. The present study was designed to elucidate a physiological change of orexin across sleep cycles and also a possible mechanism of how orexins affect vigilance states and behavior. Since a lack of orexins results in the excessive day time sleepiness (EDS) and the loss of muscle tone (cataplexy), orexin may alter the levels of neurotransmitters in the center of desynchronizing EEG activity in the hypothalamus and of regulating motor activity in the brainstem. Thus, we examined the release of histamine in the frontal cortex and norepinephrine (NE) in the thalamus of the rat after an intravenous injection of orexin-A.Intraveous injection of orexin-A (1 nmol, 2 nmol and 10 nmol) elicited the release of NE from the thalamus significantly. On the contrary, only 10 nmol of orexin-A elicted the release of histamine significantly in the frontal cortex. These results suggested that the increase in NE release may reflect the EMG activity and the increase in histamine release may reflect the EEG activity. The difference of the optimal concentration to affect on EMG and EEG may explain why the beginning of EDS is usually followed cataplexy. [Jpn J Physiol 54 Suppl:S206 (2004)]
