Fig. 3
VNS improves outcomes of nervous system diseases through multisystemic modulation. One is via the microbiota–gut–brain axis because VNS can reduce the release of H2S by gut microbiota into circulation, further reduce the lesion severity of the nervous system, and cause an M2 shift in microglia. Other possible mechanisms include amelioration of atrial fibrillation and obesity, risk factors for ischaemic stroke. Furthermore, stress is known to have negative impacts on gut flora and induce poor prognosis of CNS diseases. VNS is able to reduce responses to stress, thus helping to stop the inflammatory loop along the gut–brain axis. AF atrial fibrillation, IL-6 interleukin 6, TNF-α tumour necrosis factor-α