K 42 distribution in brain during simultaneous ventriculocisternal and subarachnoid perfusion

Abstract

The K 42 distribution in brain during simultaneous ventriculocisternal and subarachnoid perfusions has been studied. A new technique utilizing the dissecting microscope has been developed which permits perfusion of an area of the cerebral subarachnoid space in the cat. By combining this method with simultaneous ventriculocisternal perfusion, a more controlled comparison of the relative permeability of brain surfaces can be obtained. By analysis of tissue slices, it was found that the ependymal surface is approximately twice as permeable to K 42 as is the pial-glial surface. By perfusion of the subdural space, it was found that the arachnoid membrane constitutes a barrier to exchange. When K 42 distribution patterns are plotted, they differ significantly from the profiles that would be predicted on the basis of simple diffusion into a slab of brain. Analysis of experimental results shows that a large proportion of the isotope must be intracellular. Using a compartmental approach, a mathematical model is constructed by solving equations which have been modified to allow for cellular and capillary absorption processes. This model reflects what has been found experimentally.