Choline-Sigma-1R as an Additional Mechanism for Potentiation of Orexin by Cocaine

Orexin A, an endogenous peptide involved in several functions including reward, acts via activation of orexin receptors OX₁ and OX₂, Gq-coupled GPCRs. We examined the effect of a selective OX₁ agonist, OXA (17-33) on cytosolic calcium concentration, [Ca²⁺]_i, in neurons of nucleus accumbens, an important area in the reward circuit. OXA (17-33) increased [Ca²⁺]_i in a dose-dependent manner; the effect was prevented by SB-334867, a selective OX₁ receptors antagonist. In Ca²⁺-free saline, the OXA (17-33)-induced increase in [Ca²⁺]_i was not affected by pretreatment with bafilomycin A1, an endo-lysosomal calcium disrupter, but was blocked by 2-APB and xestospongin C, antagonists of inositol-1,4,5-trisphosphate (IP₃) receptors. Pretreatment with VU0155056, PLD inhibitor, or BD-1047 and NE-100, Sigma-1R antagonists, reduced the [Ca²⁺]_i response elicited by OXA (17-33). Cocaine potentiated the increase in [Ca²⁺]_i by OXA (17-33); the potentiation was abolished by Sigma-1R antagonists. Our results support an additional signaling mechanism for orexin A-OX₁ via choline-Sigma-1R and a critical role for Sigma-1R in the cocaine-orexin A interaction in nucleus accumbens neurons.