ELECTRON-MICROSCOPY OF THE BLOOD-BRAIN-BARRIER IN DISEASE

The anatomical site of the blood-brain barrier (BBB) is at the capilla ry endothelium mainly, with some contribution from astrocytes. Electro n microscopic observations of endothelial cells and perivascular astro cytes comprising the BBB in brain edema and other pathological conditi ons are reviewed in this article. The tight junctions of cerebral endo thelial cells open under several conditions such as infusion of hypero smolar solutions. Pinocytotic vesicles increase under various patholog ical conditions and fenestrae appear in blood vessels of certain brain tumors and several non-neoplastic lesions. Inflammatory cells penetra te between or through endothelial cells. In long standing lesions, end othelial cells containing various tubular structures such as Weibel-Pa lade bodies proliferate. Other alterations include surface infoldings of endothelial cells and fluid diffusion through damaged endothelium. Astrocytic alterations include abnormal junctions between astrocytic p rocesses in certain gliomas. In vivo and in vitro studies suggest that astrocytes maintain or develop certain functions of BBB. As the BBB i s disrupted, edema fluid infiltrates the brain parenchyma. Because the white matter consists of nerve fibers without demonstrable junctions, it invades between nerve fibers. In the gray matter, expansion of the fluid is limited by complicated anatomical structures. In myelinated nerve fibers, edema fluid accumulates in five separate compartments of extracellular space. (C) 1994 Wiley-Liss, Inc.