Sodium movement across the blood-brain barrier in newborn and adult rats and its autoradiographic localization

Abstract

The net rate and structural specificity of 22Na entry into newborn and adult rat brain after intravenous injection were investigated. After a single injection, the half-time of sodium entry into adult rat brain was about 75 min, into newborn brain about 40 min, a difference not related to the history of plasma specific activity. Autoradiograms were made using Kodak NTB-3 plates 15 min after the intravenous injection of 22Na. In the adult rats, areas of increased uptake included a band across dorsal medulla and ventral cerebellum at the level of the foramen of Luschka, some white matter, the lateral walls of the posterior portion of the third ventricle, and the granular and medullary layers of the cerebellum. The regions of the subfornical organ (intercolumnar tubercle) and area postrema showed increased uptake, but the density in these areas was neither greatest at these specific structures nor restricted to them. Autoradiograms of newborn brain showed the greatest sodium uptake in the germinal cell zone (subependymal matrix cells). The neocortex, newly formed cell layers of Ammon's horn and the dentate gyrus, pineal body, and subfornical organ showed increased uptake; but the subcommissural organ did not. The density in the region of the walls of the third ventricle was not consistently increased. Areas destined to be white matter showed the least uptake of all. The pattern of increased barrier permeability to sodium does not conform to the traditional pattern established by trypan blue. From these data one can see the importance of considering the blood-brain barrier as unique for each class of tracer substance, age of animal, and structural area of the central nervous system.