Nagy Z, Pettigrew K D, Meiselman S, Brightman M W
Laboratory of Neurobiology, National Institute of Neurological, Communicative Disorders and Stroke, Bethesda, MD 20892.
Brain Res. 1988 Feb 9;440(2):315-27. doi: 10.1016/0006-8993(88)91001-3.
Three purported means by which large solutes may penetrate the blood-brain barrier are: permeabilized tight junctions; vesicular transport; or channel formation across cerebral blood vessels. The role of vesicular transport has been questioned, in part, because many cytoplasmic vesicles are induced by aldehyde fixation. Cryofixation reduces this artefact and was used to see structural changes in frog cerebral endothelium made permeable to plasma solutes after perivascular exposure to hyperosmotic (3 M) urea, or injury with a cold probe (-50 degrees C). Some control and experimental frogs were made hypothermic so as to inhibit endocytosis and autolytic changes. The brains of some untreated controls were immerse-fixed in aldehydes. Other controls and all other brains of normothermic or hypothermic animals were rapidly frozen, then substituted with acetone-fixative. The interendothelial tight junctions separate partially or completely, after hyperosmotic exposure, in one third of the junctions. Blood-borne ferritin and Evans blue pass through some of the patent junctions. Junctional opening is caused by cell shrinkage, because the perimeter/area ratio of individual endothelial cells in the hyperosmotic group is significantly greater than in the control, due to a decreased area. Large 0.08-0.32-micron-wide invaginations or pits of the endothelial cell membrane characterize both cryofixed and aldehyde-fixed vessels. The pits often appear as isolated vesicles in the cytoplasm, but serial sections reveal that many communicate with either the capillary lumen or subendothelial space. No series of pits opened onto both lumen and space to form a transendothelial channel. The number of vesicles in aldehyde-fixed specimens is about 4 times greater (P less than 0.01) and in the cold injured, cryofixed brain capillary, about two times greater (P less than 0.01), than in the cryofixed control. Hyperosmotic exposure does not increase the number of pits. The permeabilization of anuran cerebral endothelium by hyperosmotic treatment or cold injury is thus by means of an intercellular rather than a transcellular route.
紧密连接通透性增加；囊泡运输；或跨脑血管形成通道。囊泡运输的作用受到了质疑，部分原因是许多细胞质囊泡是由醛固定诱导产生的。冷冻固定减少了这种假象，并用于观察蛙脑内皮细胞在血管周围暴露于高渗（3M）尿素或用冷探针（-50℃）损伤后对血浆溶质通透性增加时的结构变化。一些对照和实验蛙进行低温处理以抑制内吞作用和自溶变化。一些未处理对照的大脑用醛类进行浸没固定。其他对照以及正常体温或低温动物的所有其他大脑迅速冷冻，然后用丙酮固定剂进行置换。高渗暴露后，三分之一的连接处内皮细胞间紧密连接部分或完全分离。血源性铁蛋白和伊文思蓝通过一些开放的连接处。连接开口是由细胞收缩引起的，因为高渗组单个内皮细胞的周长/面积比显著大于对照组，这是由于面积减小所致。冷冻固定和醛固定的血管中内皮细胞膜均有0.08 - 0.32微米宽的大凹陷或小窝。这些小窝在细胞质中常表现为孤立的囊泡，但连续切片显示许多小窝与毛细血管腔或内皮下间隙相通。没有一系列小窝同时通向管腔和间隙以形成跨内皮通道。醛固定标本中的囊泡数量比冷冻固定对照大约多4倍（P小于0.01），在冷损伤的冷冻固定脑毛细血管中比冷冻固定对照大约多2倍（P小于0.01）。高渗暴露不会增加小窝的数量。因此，高渗处理或冷损伤使蛙脑内皮细胞通透性增加是通过细胞间途径而非跨细胞途径。
