Orexin-A Inhibits the High Potassium-Induced Increase in Intracellular Calcium Levels in Cultured Dorsal Root Ganglions Neurons from Carrageenan-Treated Rats

Abstract

We elucidated the effects of orexin-A in dorsal root ganglion (DRG) neurons. Immunohistochemical staining was performed to compare changes in N-methyl-daspartate receptors (NMDARs) and orexin-A in the DRG between the carrageenaninduced neuropathic pain rat model (CA) and non-algetic rats (Control). We also evaluated the inhibitory effects of orexin-A by measuring [Ca²⁺] i. Using immunohistochemistry, orexin-A expression was observed in both the posterior and anterior horns of the spinal cord. No major difference was observed between the groups. Using immunohistochemistry, orexin-A expression was also observed in neurons in the DRG, and no major difference was observed between the groups. NMDAR expression levels in the posterior horn of the spinal cord and the DRG were not quantitatively determined, but the overall staining intensity of NMDAR was higher in CA than in control rats. Also, in the DRG neurons of the CA rats, administration of orexin-A significantly suppressed the increase in [Ca²⁺] i due to depolarization stimulation caused by high K⁺. Thus, the anti-nociceptive effect was due to an increase in orexin-A. Furthermore, orexin-A may have specifically acted on L-type calcium channels.