Orexin-a activates phospholipase C- and protein kinase C-mediated Ca2+ signaling in dopamine neurons of the ventral tegmental area

The orexin-orexin receptor system has been implicated in the regulation of wakefulness/sleep states. Behavioral and psychostimulant effects of orexins have also been shown. Mesolimbic dopamine neurons in the ventral tegmental area (VTA) are implicated in the regulation of reward and wakefulness/sleep, In the present study, we examined the effect of orexin-A on cytosolic [Ca2+](i) concentration ([Ca2+]) in the isolated rat VTA dopamine neurons. Orexin-A (10(-12)-10(-8)M) concentration dependently increased [Ca2+](i) in dopamine-containing neurons. The [Ca2+](i) responses to orexin-A were inhibited under Ca2+-free conditions and by blockers of voltage-gated Land N-type [Ca2+](i) channels, nitrendipine and omega -conotoxin, respectively. The [Ca2+](i) responses were also abolished by a phosphatidylcholine-specific phospholipase C inhibitor, D609, and a protein kinase C (PKC) inhibitor, calphostin C. A PKC activator, TPA, mimicked orexin-A in increasing [Ca2+](i). These results indicate that orexin-A increases [Ca2+](i) in VTA dopamine neurons via phosphatidylcholine-specific PLC- and PKC-mediated activation of L- and N-type Ca2+ channels. This effect may serve as the mechanism by which orexin regulates wakefulness/sleep states and exerts its behavioral and psychostimulant effects. NeuroReport 12:1885-1889 (C) 2001 Lippincott Williams & Wilkins.