TH and Parkinson disease: TUNEL and TH double labeling were employed to validate the effect of EVs on apoptosis of dopaminergic neurons, the results of which demonstrated that the number of TUNEL+ cells in sham-operated mice was very small, while the number of TUNEL+/TH+ cells was reduced in PD mice injected with MSC–EV–NC mimic, and the number being obviously decreased in PD mice injected with MSC–EV–miR-181a–2–3p mimic (Fig. 9I).