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Neurosci Lett. 2002 Apr 26;323(2):93-6.

The effect of orexin-A and -B on the histamine release in the anterior hypothalamus in rats.

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Department of Medical Physics, School of Allied Health Sciences, Faculty of Medicine, Osaka University, 1-7 Yamadaoka, Suita, Osaka 565-0871, Japan.


The neuropeptides orexin-A and -B have been reported to be appetite-stimulating peptides, but they are also known as important factors that control arousal state. We studied the effects of orexin-A and -B on the hypothalamic histamine release using in vivo microdialysis. A significant and sustained increase in histamine release was observed by intracerebroventricular injection of 1 nmol of orexin-A, but not by the same dose of orexin-B. An increased dose of orexin-B to 5 nmol facilitated histamine release, although this effect was much less potent than orexin-A. These findings suggest that both of the orexins play important roles in the regulation of waking through the activation of histaminergic system.

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