Changes in the water and electrolyte pattern of the brain and of the intracranial pressure during development in rabbits.

During its development the brain becomes dehydrated pari passu with growth and myelination and the electrolyte pattern changes from high sodium, low potassium to the opposite. The latter change is complete or virtually so in some species at term but in others the reversal is a postnatal occurrence. We have examined these features in rabbits of several ages and have measured the intracranial pressure at intervals during development as well. At or near both the water content of the brain is very high compared to that found later and the fetal electrolyte pattern is transitional in that the K/Na ratio is approximately one but not as high as in the mature brain. The intracranial pressure is lower in the newborn pups than it is later in development. Unlike that in mature animals the premature and young term rabbit brain is unable to affect ionic movements appropriate to the protection of the volume of the brain.