A scanning electron-microscopic analysis of the intraparenchymal brain vasculature following experimental hypertension

The effects of acute systemic hypertension on the intraparenchymal cerebral vasculature of cats was assessed by morphological means. Intravenous horseradish peroxidase administration coupled with light microscopy was employed to identify brain sites manifesting hypertension-induced peroxidase extravasation and therein the luminal surface of the intraparenchymal vasculature was examined with scanning electron microscopy (SEM). Comparable SEM studies were also conducted within sites reflecting no altered peroxidase permeability. Via these techniques, hypertension was recognized to evoke significant vascular change throughout the neuraxis. The luminal endothelia of that vasculature contained within the peroxidase extravasation sites demonstrated numerous plasmalemmal pits and the occasional presence of balloon- and crater-like lesions which were localized along the marginal lines. In sites demonstrating no peroxidase exudation, these plasmalemmal pits were infrequent; yet, the balloon and crater-like lesions, again localized along the marginal lines, were now conspicuous and regular endothelial features. Within the peroxidase extravasation sites, plasmalemmal pits could be identified within minutes of the onset of the hypertensive event, while in all loci endothelial balloons were observed prior to the appearance of craters. These results demonstrate that numerous plasmalemmal pits, the SEM correlates of vesicles observed with transmission electron microscopy, appear to be temporally and spatially linked to the peroxidase extravasation and as such this may suggest that these phenomena are causally linked. The significance of endothelial balloons and craters, which are most prevalent in sites not manifesting peroxidase extravasation, is unclear; however, based on a parallel study conducted in the pial vasculature, the suggestion is advanced that their appearance may be linked to the loss of microvascular autoregulation.