Circulating EVs from hyperoxia-exposed rats induce brain inflammatory injury when adoptively transferred into normal neonatal rats. (A) and (B): SVZ. (C) and (D): SGZ. (E) and (F): Cortex. Immunostaining for AIF-1, a microglia marker (brown signals) demonstrated enlarged activated microglial cells (black arrows) in the SVZ (B), SGZ (D) and cortex (F) of rats receiving O2- EVs injection. Scale bar: 50 µm. qRT-PCR showed increased gene expression of IL-1α, IL-18, TNF-α, fibronectin (FN1) and platelet derived growth factor receptor beta (PDGFRβ) in brain tissues of O2-EVs injected rats compared to RA-EVs injected rats ((G), n = 5/group, *P < 0.05). When compared to RA-EVs injected rats (H), the TUNEL assay showed increased dead cells (white arrows) in the SVZ of O2-EVs injected rats (I) ((J), n = 10/group, **P < 0.01). Scale bar: 50 µm.