Bilateral transcranial direct-current stimulation promotes migration of subventricular zone-derived neuroblasts toward ischemic brain

Abstract

Ischemic insult stimulates proliferation of neural stem cells (NSCs) in the subventricular zone (SVZ) after stroke. However, only a fraction of NSC-derived neuroblasts from SVZ migrate toward poststroke brain region. We have previously reported that direct-current stimulation guides NSC migration toward the cathode in vitro. Accordingly, we set up a new method of transcranial direct-current stimulation (tDCS), in which the cathodal electrode is placed on the ischemic hemisphere and anodal electrode on the contralateral hemisphere of rats subjected to ischemia-reperfusion injury. We show that the application of this bilateral tDCS (BtDCS) promotes the migration of NSC-derived neuroblasts from SVZ toward the cathode direction into poststroke striatum. Reversing the position of the electrodes blocks the effect of BtDCS on the migration of neuroblasts from SVZ. BtDCS protects against neuronal death and improves the functional recovery of stroke animals. Thus, the migration of NSC-derived neuroblasts from SVZ toward poststroke brain region contributes to the effect of BtDCS against ischemia-induced neuronal death, supporting a potential development of noninvasive BtDCS as an endogenous neurogenesis-based stroke therapy.

Keywords: ischemic stroke; neural stem cells; stem cell migration; subventricular zone; transcranial direct‐current stimulation.

FIGURE 1

A schematic diagram showing the setup of BtDCS application. The effect of BtDCS on NSC‐derived neuroblast migration was tested in the injured rat brain subjected to MCAO. A constant current stimulator was used. The electrodes were positioned on each side of the cranium over the temporal area in a symmetrical manner, with the cathodal electrode placed on the ischemic hemisphere and the anodal electrode on the contralateral hemisphere, which allowed the currents to pass through the SVZ. The contact area of the electrode toward the skull is 7.0 mm².

FIGURE 2

Colabeling of Dcx and BrdU in the ipsilateral striatum of MCAO rat after BtDCS treatment. Representative images show that BtDCS application for 150 μA for 30 min per day for 12 days at 2 days after MCAO in nonanesthesia conditions increases the number of colabeling of Dcx and BrdU in ipsilateral striatum at 14 days after ischemia–reperfusion injury. Scale bar = 100 μm.

FIGURE 3

BtDCS treatment increases the number of colabeled Dcx and BrdU in the ipsilateral striatum of MCAO rat. Summarized data show that BtDCS increases the colocalization of BrdU/Dcx in the ischemic striatum at 14 days after ischemia–reperfusion (n = 7, *p < 0.05 vs. I/R, Student t test).

FIGURE 4

Colabeling of Dcx with GFP‐labeled cells in the ipsilateral striatum of MCAO rat after BtDCS treatment. (A–B) Representative images show that BtDCS exposure of 150 μA for 30 min per day for 2 days after MCAO for 12 days, increases the colocalization of Dcx with GFP in ipsilateral striatum at 14 days after ischemia–reperfusion injury. Scale bar = 100 μm. (C) BtDCS exposure of 150 μA for 30 min per day for 2 days after MCAO for 12 days, with the anodal electrode placed on the ischemic hemisphere, decreases the colocalization of GFP with Dcx in the ischemic striatum at 14 days after ischemia–reperfusion injury. Scale bar = 100 μm.

FIGURE 5

BtDCS increases the colocalization of Dcx with GFP‐labeled cells in ipsilateral striatum. Summarized data show that BtDCS treatment for 12 days increases the colocalization of GFP/Dcx in the ischemic striatum at 14 days after ischemia–reperfusion injury (n = 8, *p < 0.05 vs. I/R, ^# p < 0.05 vs. I/R + BtDCS, ANOVA test).

FIGURE 6

BtDCS treatment reduces the infarct volume. (A‐B) Representative images of Nissl staining show that BtDCS application for 150 μA for 30 min per day for 12 days at 2 days after MCAO reduces the infarct volume of MCAO animals at 14 days after ischemia–reperfusion injury. IR = ischemia–reperfusion injury. (C) Summarized data of Nissl staining indicate that BtDCS application for 150 μA for 30 min per day for 12 days at 2 days after MCAO reduces the infarct volume of MCAO animals at 14 days after ischemia–reperfusion injury (n = 8 rats for each group, *p < 0.05 vs. I/R, Student t test).

FIGURE 7

BtDCS improves the neurobehavioral function of stroke animals. (A) Summarized data show that rats treated with BtDCS for 150 μA for 30 min per day for 12 days have significantly lower scores of mNSS tests on day 14 (I/R group score = 7.2 ± 1.02; I/R + BtDCS score = 4.8 ± 0.77) and day 28 (I/R group score = 6.2 ± 0.85; I/R + BtDCS score = 4.0 ± 0.67) after MCAO, (n = 7 rats for each group, *p < 0.05 vs. I/R; ANOVA and subsequent post hoc Bonferroni's test). (B) Summarized data show that rats treated with BtDCS for 150 μA for 30 min per day for 12 days have significantly lower scores of beam‐walking test on day 14 (I/R group score = 3.2 ± 0.48; I/R + BtDCS score = 2.1 ± 0.35) and day 28 (I/R group score = 2.8 ± 0.43; I/R + BtDCS score = 1.7 ± 0.22) after MCAO, (n = 9 rats for each group, *p < 0.05 vs. I/R; ANOVA and subsequent post hoc Bonferroni's test). (C) Summarized data show that rats treated with BtDCS for 150 μA for 30 min per day for 12 days have a significantly higher ratio of a modified sticky tape test on day 14 (I/R group score = 0.21 ± 0.03; I/R + BtDCS score = 0.40 ± 0.06) and day 28 (I/R group score = 0.24 ± 0.03; I/R + BtDCS score = 0.46 ± 0.06) after MCAO (n = 7 rats for each group, *p < 0.05 vs. I/R; ANOVA and subsequent post hoc Bonferroni's test).