Water, electrolytes, and extracellular space in hydrated and dehydrated brains

Abstract

After intravenous infusion of distilled water (20% of body wt) the water content of rabbit brain was increased by about 10%. The brain lost sodium (11%), chloride (12%), but no potassium. A decrease of the water content (about 18%) was found after injection of 50% glucose (5% of body wt) in mice. It has been found previously in rabbits that the brain also loses sodium (25%) and chloride (21%) during dehydration, but no potassium. The Na and Cl ions in hydrated and dehydrated brain seem to be lost from the extracellular space. The ratio between the extra- and intracellular compartment can be expected to be smaller in the hydrated and especially in the dehydrated brains than in normal tissue. Electron micrographs of the molecular layer of the cerebellar cortex of mice hydrated with distilled water and dehydrated with 50% glucose were prepared by freeze substitution. The tissue was frozen within 30 sec of circulatory arrest. The micrographs were similar in appearance to those of normal animals. The magnitude of the extracellular space did not seem different in hydrated, but was perhaps somewhat smaller in dehydrated cerebellum. Asphyxiation caused a reduction of the extracellular space.