Extracellular space of rat cerebral cortex

Abstract

Investigators have used a number of techniques in attempts to measure the size of the extracellular space (ECS) of the brain. Currently, general agreement on the size of the ECS is lacking; thus a definitive measurement of this space is needed. A method of ventriculo-cisternal perfusion of the rat brain, in vivo, was developed in which 14C-labeled inulin was used as an extracellular indicator. Functionally nephrectomized 300- to 350-g rats were injected intravenously with 1 [mu]c inulin-14c/100 g body wt. After 30 min. the animals were perfused with artificial CSF [cerebro-spinal fluid] the inulin concentration of which was equal to that of the plasma. With such a method it is possible to circumvent the blood-brain barrier and many of the technical problems encountered in previous studies. The insulin space of the cerebral cortex reached a constant value of 13.5-14.5% of the wet wt after perfusion for 6 hr.