An ultrastructural quantitative method for the evaluation of the permeability to horseradish peroxidase of cerebral cortex endothelial cells of the rat.

A quantitative method for the evaluation of the importance of pinocytotic phenomena in cerebral cortex capillaries is proposed. The method involved the counting of labeled "caveolae intracellulares" in endothelia cells with the use of horseradish peroxidase as a tracer molecule. A mean pinocytotic value per capillary is then computed. It is demonstrated that the value obtained after irradiation of the brain is higher than in control animals. This information may provide an ultrastructural quantitative approach to the analysis of the blood brain barrier and of other problems related to vascular permeability of the cerebral cortex.