Mechanisms of blood-brain barrier breakdown after microembolization of the cat's brain

Unilateral microembolization of the cat brain with carbonized microspheres 15 microns in diameter ten minutes (min) before death induced multifocal disruption of the blood-brain barrier (BBB) to horseradish peroxidase (HRP) in nine adult cats. The gross pattern of HRP extravasates was studied: (a) after five min of in vivo circulation, (b) following infusion of HRP immediately before chemical fixation, and (c) following infusion of HRP after 60 min of aldehyde fixation. Examination of the material from the three different experimental groups revealed no qualitative differences at the light microscopic level; specific features such as ring-shaped extravasations of HRP occurred irrespective of the mode of tracer injection. Tracer-filled pinocytotic vesicles and tubular profiles were abundant in the vascular endothelium after in vivo circulation of HRP, but were virtually absent after supravital and postmortem HRP administration. The results suggest that BBB breakdown for proteins after microembolization is not an energy-dependent process mediated by either pinocytosis or tubular-endothelial channel formation.