Bulk flow of interstitial fluid after intracranial injection of Blue Dextran 2000

Abstract

The hypothesis that there is bulk flow of cerebral interstitial fluid (ISF) has been examined in rats by following the intracerebral distribution of Blue Dextran 2000. Guide tubes were implanted into the caudate nucleus using standard stereotaxic technique. One day after implantation, 0.5 μl of saline containing Blue Dextran was injected into brain. The extent and pattern of dye distribution were determined 15 min and 24 hr after injection by microscopic examination of brains sectioned using a freezing microtome. Blue Dextran was initially confined to the base of the injector cannula, but spread extensively over 24 hr. Characteristics of dye distribution indicate that Blue Dextran is transported away from the injection site by bulk flow of cerebral ISF, possibly along the course of cerebral blood vessels. There was no evidence of bulk flow in rats pretreated with dexamethasone or with an injection-implantation interval of 7 days, suggesting that edema fluid contributes to the observed flow of ISF. Results indicate the need to reevaluate the role of perivascular spaces in net fluid exchange between brain and cerebrospinal fluid.