In this study, the roles of exosomes (Exo) from bone marrow mesenchymal stem cells (BMSCs) in attenuating early brain injury (EBI) in rat brain after subarachnoid hemorrhage (SAH) had been investigated. The male Sprague-Dawley rats (300–350 g) were used to establish the SAH model using endovascular perforation method. The animals were randomly divided into three groups: sham (n = 25), SAH+PBS (n = 42), and SAH+Exo groups (n = 33). At 1 h after SAH, Exo or phosphate-buffered saline (PBS) was administered by femoral vein injection. The effects of Exo on the mortality, neurological function, brain water content, and blood–brain barrier (BBB) were explored. Furthermore, the expressions of miRNA129-5p and high-mobility group box 1 protein (HMGB1) after Exo treatment were also detected. In addition, immunohistochemistry and western blot were applied to investigate the mechanism of Exo's effects. The results indicated that Exo could improve the neurological functions, reduce brain water content and maintain BBB integrity after SAH. After Exo treatment, the expression of miRNA129-5p was significantly increased, whereas the RNA level of HMGB1 was decreased. The protein levels of proinflammatory and proapoptosis factors, such as HMGB1, Toll-like receptor-4 (TLR4), tumor necrosis factor-α, and p53, were increased after SAH, which were significantly declined after Exo application. The results indicated that Exo from BMSCs could alleviate EBI after SAH through miRNA129-5p's anti-inflammation and antiapoptosis effects through quenching the activity of HMGB1-TLR4 pathway.

Recent studies have proposed three lymphatic drainage systems in the brain, that is, the glymphatic system, the intramural periarterial drainage pathway, and meningeal lymphatic vessels, whose roles in various neurological diseases have been widely explored. The glymphatic system is a fluid drainage and waste clearance pathway that utilizes perivascular space and aquaporin-4 protein located in the astrocyte endfeet to provide a space for exchange of cerebrospinal fluid and interstitial fluid. The intramural periarterial drainage pathway drives the flow of interstitial fluid through the capillary basement membrane and the arterial tunica media. Meningeal lymphatic vessels within the dura mater are involved in the removal of cerebral macromolecules and immune responses. After ischemic stroke, impairment of these systems could lead to cerebral edema, accumulation of toxic factors, and activation of neuroinflammation, while restoration of their normal functions can improve neurological outcomes. In this review, we summarize the basic concepts of these drainage systems, including drainage routes, physiological functions, regulatory mechanisms, and detection technologies. We also focus on the roles of lymphatic drainage systems in brain injury after ischemic stroke, as well as recent advances in therapeutic strategies targeting these drainage systems. These findings provide information for potential novel strategies for treatment of stroke.

The nature of brain interstitial fluid (ISF) has long been a subject of controversy. Most of the previous studies on brain ISF were carried out in vitro. In the present study, a novel method was developed to characterize ISF in the living rat brain by magnetic resonance (MR) imaging using gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) as a tracer. Sprague Dawley rats (n=8) were subjected to MR scanning before and after the introduction of Gd-DTPA into the caudate nucleus. A one-way drainage of brain ISF was demonstrated on the dynamic MR images. According to the traditional diffusion model, the diffusion and clearance rate constants of the tracer within brain extracellular space (ECS) were derived as (3.38+−1.07)×10⁻⁴ mm² s⁻¹ and (7.60±4.18)×10⁻⁵ s⁻¹. Both diffusion and bulk flow contributed to the drainage of ISF from the caudate nucleus, which demonstrated an ISF-cerebrospinal fluid confluence in the subarachnoid space at the lateral and ventral surface of the brain cortex at 3 h after the injection. By using this newly developed method, the brain ECS and ISF can be quantitatively measured simultaneously in the living brain, which will enhance the understanding of ISF and improve the efficiency of drug therapy via the brain interstitium.