Electrical stimulation promotes BDNF expression in spinal cord neurons through Ca(2+)- and Erk-dependent signaling pathways.

Brief electrical stimulation has been shown to be effective in promoting neuronal regeneration following peripheral nerve injury. These effects are thought to be mediated largely by the upregulation of the expression of brain-derived neurotrophic factor (BDNF) in spinal cord neurons. However, the molecular mechanisms by which electrical stimulation can promote BDNF expression are not known. The mechanism involved in BDNF expression after electrical stimulation was explored in this study. Immunohistochemistry and Western blotting were used to test BDNF expression. Confocal microscopy was utilized to study intracellular Ca(2+) volume. Immunohistochemistry and Western blotting confirmed that brief electrical stimulation increased BDNF expression in spinal cord neurons both in vivo and in vitro. Treatment of cultured neurons with nifedipine, an inhibitor of voltage-gated calcium channels, significantly reduced the BDNF increase produced by electrical stimulation, and an inhibitor of Erk completely abolished the effect of electrical stimulation. Levels of BDNF expression in the presence of the Erk inhibitor were lower that in unstimulated and untreated controls, indicating that Erk activation is required to maintain baseline levels of BDNF. Confocal microscopy using a Ca(2+)-sensitive fluorochrome revealed that electrical stimulation is accompanied by an increase in intracellular Ca(2+) levels; the increase was partly blocked by nifedipine. These findings argue that electrical stimulation increases BDNF expression in spinal cord neurons by activating a Ca(2+)- and Erk-dependent signaling pathways.