Abstract

We demonstrated involvement of the ventral tegmental area (VTA) dopaminergic system in orexin-induced hyperlocomotion and stereotypy in rats. In double-label immunohistochemical study of rat brain, we found that tyrosine hydroxylase (TH)-immunoreactive cells in the VTA received innervation from orexin immunoreactive-fibers. Orexin-A induced an increase in [Ca 2+] i in isolated A10 dopamine neurons in a dose-dependent manner. In behavioral studies, we found that orexin-A induced hyperlocomotion, stereotypy and grooming behavior when administered centrally in rats, and these effects were abolished by dopamine D 2 (haloperidol and sulpiride) or D 1 (SCH23390) antagonists. These results suggest that the orexin-induced hyperlocomotion, stereotypy and grooming behavior are mediated by the dopaminergic system and this pathway might be involved in orexin-induced emotional responses.

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