Transcranial-Direct-Current-Stimulation Accelerates Motor Recovery After Cortical Infarction in Mice: The Interplay of Structural Cellular Responses and Functional Recovery

Background Transcranial direct current stimulation (tDCS) promotes recovery after stroke in humans. The underlying mechanisms, however, remain to be elucidated. Animal models suggest tDCS effects on neuroinflammation, stem cell proliferation, neurogenesis, and neural plasticity. Objective In a longitudinal study, we employed tDCS in the subacute and chronic phase after experimental focal cerebral ischemia in mice to explore the relationship between functional recovery and cellular processes. Methods Mice received photothrombosis in the right motor cortex, verified by Magnetic Resonance Imaging. A composite neuroscore quantified subsequent functional deficits. Mice received tDCS daily: either 5 sessions from day 5 to 9, or 10 sessions with days 12 to 16 in addition. TDCS with anodal or cathodal polarity was compared to sham stimulation. Further imaging to assess proliferation and neuroinflammation was performed by immunohistochemistry at different time points and Positron Emission Tomography at the end of the observation time of 3 weeks. Results Cathodal tDCS at 198 kC/m 2 (220 A/m 2 ) between days 5 and 9 accelerated functional recovery, increased neurogenesis, decreased microglial activation, and mitigated CD16/32-expression associated with M1-phenotype. Anodal tDCS exerted similar effects on neurogenesis and microglial polarization but not on recovery of function or microglial activation. TDCS on days 12 to 16 after stroke did not induce any further effects, suggesting that the therapeutic time window was closed by then. Conclusion Overall, data suggest that non-invasive neuromodulation by tDCS impacts neurogenesis and microglial activation as critical cellular processes influencing functional recovery during the early phase of regeneration from focal cerebral ischemia.