Identifying lymphatic drainage pathway of protein from subarachnoid hemorrhage rat brain using fluorescence Evans blue-labeled albumin injected into caudate-putamen

Abstract

Objective To investigate the pathway of lymphatic drainage of proteins from cerebral parenchyma in subarachnoid hemorrhage rat models. Methods Healthy adult male Wistar rats were divided into Saline group, Evans blue-labeled albumin (EBA) group, and SAH + EBA group. SAH models were produced by double injection of autologous arterial blood into cisterna magna. Using a modified microinjection method, EBA was injected into left candate-putamen of the EBA group and EBA + SAH group rats. In Saline control group, saline was injected. After injection, at 12 hours, 1 day, 2 days, 3 days and 5 days, the animals were sacrificed and the fluorescence signals of EBA were imagined and analyzed along the possible lymphatic drainage pathway, e.g. the brain tissue, the wall of common carotid artery, and cervical lymphatic nodes. Results One day after injection, in EBA group, the fluorescence of EBA initially appeared on the left of the brain, the wall of common carotid artery, left lateral cerebral ventricle, and the perivascular spaces of cerebral vessels. The fluorescence signals gradually expanded to the opposite side.Large amount of fluorescence granules accumulated in the outer layer of common carotid artery. Fluorescence was also found in cervical lymphatic nodes. Two days after injection in this group, the density of fluorescencein the brain became weaker while the density of fluorescence in rhinencephalon became stronger. The fluorescence of EBA was found in lymphatic nodes adjacent to abdominal aorta. In SAH + EBA group,reduced amount and velocity of the drainage of EBA from left caudate-putamen to rhinencephalon, cervical lymphatic nodes, and lymphatic nodes adjacent to abdominal aorta were observed. From 12 hours to 5 days after injection, fluorescence intensity of EBA in deep cervical lymphatic nodes in SAH + EBA group(8.9 ±2. 0, 11.9 ± 2. 5, 17.4 ± 3.7, 26.7 ± 4. 5 and 59.0 ± 8. 1 ) were lower than those in EBA group ( 14. 5 ±3.2, 27.5 ±7.4, 60.3 ±12.3, 138.0±12.0 and 108. 1 ±13.4, F=13. 17, 24.04, 66.81, 302.77 and 59.36, P ＜ 0. 01 ). From 2 to 5 days, fluorescence intensity of EBA in lymphatic nodes adjacent to abdominal aorta was also lower in SAH + EBA group( 11.0 ± 1.5, 12. 5 ±2. 8, 23.6 ±3. 2) than those in EBA group(26. 3 ±5.9, 47.5 ±9.6, 41.0 ±9.3; F =38. 17, 72.52, 19.01, P ＜0.01). Conclusion SAH can result in reduced drainage of macromolecular substances, e.g. protein, from the brain via lymphatic pathway. Key words: Subarachnoid hemorrhage; Macromolecular substances; Lymphatic system; Rats