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

Abstract

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.

The Orexin OX1Receptor Regulates Ca2+Entry via Diacylglycerol-Activated Channels in Differentiated Neuroblastoma Cells

“…At low agonist concentrations, a measurable Ca 2ϩ release from intracellular stores was essentially absent. This is in agreement with previous studies van den Pol, 1999;Lund et al, 2000;Uramura et al, 2001;Holmqvist et al, 2002;Willie et al, 2003;Kohlmeier et al, 2004) and indicates Ca 2ϩ entry as a primary OX 1 R response. In neuronal cells, a Ca 2ϩ elevation in response to G-protein-coupled receptors could be the consequence of several different mechanisms, including activation of VGCC, reversal of electrogenic Na ϩ /Ca 2ϩ exchange, or phospholipase C-linked Ca 2ϩ store discharge with a consequent activation of storeoperated channels.…”

“…The [Ca 2ϩ ] i can increase in cells by a variety of mechanisms, including depolarization-induced opening of voltagegated calcium channels (VGCCs), opening of nonselective cation channels, release from intracellular stores, as well as reversal of electrogenic Na ϩ /Ca 2ϩ exchanger. An increase in [Ca 2ϩ ] i during OXR stimulation is evident in neurons (van den Uramura et al, 2001;Kohlmeier et al, 2004), and it is also observable in different cell types used for heterologous expression (Sakurai et al, 1998;Smart et al, 1999;Holmqvist et al, 2002).…”

Hypocretin/Orexin Selectively Increases Dopamine Efflux within the Prefrontal Cortex: Involvement of the Ventral Tegmental Area

“…Further, VTA and substantia nigra neurons express HCRT1 and HCRT2 receptor mRNA (Marcus et al, 2001). Finally, in vitro, HCRT-1 activates VTA (though not substantia nigra) DA neurons (Uramura et al, 2001;Korotkova et al, 2002Korotkova et al, , 2003. Combined, these observations suggest that HCRT modulates DA neurotransmission and that this action may contribute to HCRT-induced alterations in behavioral state and state-dependent processes.…”

“…DA systems have also been implicated in the modulation of behavioral state and state-dependent processes, particularly under high arousal appetitive and aversive conditions (Trulson, 1985;Smith et al, 1992;Arnsten et al, 1994;Isaac and Berridge, 2003). Thus, it is of interest that VTA and substantia nigra neurons express HCRT receptor mRNA (Marcus et al, 2001) and that HCRT activates VTA (though not substantia nigra) DA neurons in vitro (Uramura et al, 2001;Korotkova et al, 2002Korotkova et al, , 2003. To examine initially the modulatory actions of HCRT on DA neurotransmission in vivo, the current studies utilized microdialysis measures of DA release within the PFC and Acc in the unanesthetized rat.…”

Role of Orexin-1 Receptor Mechanisms on Compulsive Food Consumption in a Model of Binge Eating in Female Rats

“…Neuropeptides that are produced in the LH can modulate the activity of VTA-DA and striatal neurons. OX-containing neurons project from the LH to the VTA, where the OX 1 R plays a key role in regulating mesolimbic DA transmission and the rewarding properties of various drugs of abuse and food (Cason et al, 2010;Uramura et al, 2001;Zheng et al, 2007). Furthermore, BE episodes may be controlled through a specific influence on reward and reinforcement processes for HPF.…”