Deoxynucleoside and vitamin transport into the central nervous system.

Several essential substances for the mammalian brain including certain vitamins and deoxynucleosides do not enter the brain in appreciable amounts directly through the cerebral capillaries, the blood-brain barrier; rather these substances are transported from blood into cerebrospinal fluid (CSF) by specific, carrier-mediated transport systems in the choroid plexus, the anatomic locus of the blood-CSF barrier. From the CSF, these substances then enter the brain. The evidence supporting the notion that the choroid plexus is important in the transfer of ascorbic acid, folates, and pyrimidine deoxynucleosides from blood into CSF is summarized. This evidence provides strong support for the theory that the CSF is, in fact, a nourishing liquor, although an incomplete one, for developing and adult mammalian brain.