Composition of fluid obtained from choroid plexus tissue isolated in a chamber in situ

A method is described for isolating a segment of the choroids plexus in the lateral ventricle of the cat brain in a chamber in situ. The electrolyte concentrations and protein content of serum, an ultra filtrate of serum (UF), cisterna-magna fluid CMF) and the fluid accumulated in the chamber (CF) were compared with fluid collected simultaneously from the choroids plexus (CPF) in the contralateral ventricle by another technique. The concentration of K+ in CPF was lower than in an UF, a finding which may be interpreted as evidence for regulation of K+ by an active transport process at the choroids plexus. The concentrations of Na+, K+, Cl- and Ca2+ were the same in CPF and CF, while the concentration of Mg2+ was significantly higher in CPF. The rate of fluid formation in the chamber was 0.4 µl/min/mg of tissue, a value in good agreement with reports in the literature. On the basis of regression analysis significant correlation was found between electrolyte values and the protein content of CF. It was suggested the plasma is the probable source of protein in CF and that K+ and probably Ca2+ and Mg2+ are subject to active homeostatic regulation by the choroids plexus. The results demonstrate that the chamber method for isolating a segment of the choroid plexus in situ provides a valid method for studying choroid plexus function free from the influence of surrounding neural tissue and, for the first time, to be able to control the osmotic, ionic and chemical composition of the fluid on the c.s.f. side of the choroid plexus during the study.