The distribution of native albumin and foreign albumin injected into lateral ventricles of prenatal and neonatal rat forebrains

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Abstract
Several plasma proteins are found within the cells of the developing brain of many species, with a distribution pattern which changes during development, but the origin of such proteins is in dispute. The experiments described here were designed to test the hypothesis that some developing brain cells are able to take up plasma proteins. The distribution of the plasma protein albumin has been studied in the rat forebrain from the 14th day of gestation until birth. Although present within the cerebrospinal fluid and plasma from the earliest age studied, albumin was not seen within cells of the developing forebrain until day 16E or 17E. A foreign protein, sheep albumin, was injected into the ventricles at days 14E, 16E, 18E, 20E and on the day of birth. Sheep albumin can be detected in the presence of rat albumin because the antibody to sheep albumin does not cross-react with rat albumin. The sheep albumin was taken up very rapidly into cells of the ventricular zone at the later but not the earlier ages, thus mimicking the distribution of the naturally occurring rat albumin. After the foreign albumin had been left within the ventricle for several hours, some of the cells of the cortical plate also contained the protein, again mimicking the normal distribution of albumin. These findings suggest that the presence of albumin within cells of the developing rat forebrain can largely be attributed to uptake rather than synthesis.