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 psycho-stimulant 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 L- and 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.
Uramura
K
K
Department of Neuropsychiatry, Faculty of Medicine, Kagoshima University, Kagoshima 890-8520, Japan.
Funahashi
H
H
Muroya
S
S
Shioda
S
S
Takigawa
M
M
Yada
T
T
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D020864:Calcium Channels, N-Type / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism / Q000494:pharmacology*; D002478:Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D009434:Neural Pathways / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D009479:Neuropeptides / Q000378:metabolism / Q000494:pharmacology*; D000068797:Orexins; D011493:Protein Kinase C / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012890:Sleep / Q000187:drug effects / Q000502:physiology; D010738:Type C Phospholipases / Q000187:drug effects* / Q000378:metabolism; D017557:Ventral Tegmental Area / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D014851:Wakefulness / Q000187:drug effects / Q000502:physiology
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D000068797:Orexins; D011493:Protein Kinase C; D010738:Type C Phospholipases; D004298:Dopamine