Microglia mediate synaptic plasticity induced by 10 Hz repetitive transcranial magnetic stimulation

Microglia—the resident immune cells of the central nervous system—sense the activity of neurons and regulate physiological brain functions. They have been implicated in the pathology of brain diseases associated with alterations in neural excitability and plasticity. However, experimental and therapeutic approaches that modulate microglia function in a brain-region-specific manner have not been established. In this study, we tested for the effects of repetitive transcranial magnetic stimulation (rTMS), a clinically employed non-invasive brain stimulation technique, on microglia-mediated synaptic plasticity. 10 Hz electromagnetic stimulation triggered a release of plasticity-promoting cytokines from the microglia in organotypic brain tissue cultures, while no changes in microglial morphology or microglia dynamics were observed. Indeed, substitution of tumor necrosis factor alpha (TNFα) and interleukin 6 (IL6) preserved synaptic plasticity induced by 10 Hz stimulation in the absence of microglia. Consistent with these findings, in vivo depletion of microglia abolished rTMS-induced changes in neurotransmission in the medial prefrontal cortex (mPFC) of anesthetized mice. We conclude that rTMS affects neural excitability and plasticity by modulating the release of cytokines from microglia.