Brain Extracellular Space and the Sink Action of Cerebrospinal Fluid

Abstract

To BE PRESENTED here are results of a series of animal experiments intended to measure the volume of extracellular space (ECS) in rabbit brain. These experiments were designed to test the hypothesis that a sink action of cerebrospinal fluid (CSF) removed solutes from nervous tissue ECS, resulting in substantial error in those methods based upon the volume of distribution of tracer substances believed to remain confined to the ECS when these substances were introduced into brain by way of blood. Sink action refers to diffusion of solutes down a concentration gradient from a region of high concentration to one of lower concentration. In the usual method of measuring the volume of ECS of a tissue, an indicator substance that remains outside cells (an ECS label) is introduced into the blood and its concentration maintained constant for a time sufficient to allow the label to pass through the capillary walls in