The longterm goal of the proposed studies is to elucidate the mechanisms by which transport systems in the barriers of the central nervous system (CNS) mature. Funds for pilot studies are requested to begin a major research program on the developmental aspects of transport of biologically active compounds in the choroid plexus and blood brain barrier (BBB). These pilot studies will focus on mechanisms of transport of taurine, a neuromodulator, because this beta-amino acid is critical for normal development of the brain, and deficiency is associated with severe neurological dysfunction. Because data in the literature suggest that taurine does not enter the CNS via the BBB, the underlying hypothesis of this proposal is that taurine, a polar compound, is transported both into and out of the CSF by specific mechanisms in the choroid plexus. This hypothesis is supported by preliminary data from this laboratory suggesting that there is an Na+- dependent system for the transport of taurine in the choroid plexus. The proposed studies are divided into two major sections: I. Mechanisms of taurine transport and II. Development of taurine transport systems. To elucidate the mechanisms of taurine transport and the importance of these mechanisms to the biological disposition of taurine in the brain, we propose integrated in vitro/in vivo studies. In the in vivo studies using lateral ventricular injection, ventriculocisternal perfusion, and a novel approach combining dual radioisotopes, microdialysis, and deconvolution analysis, we will test the hypotheses that taurine enters the brain via the choroid plexus and that its clearance from CSF involves facilitated or active transport. The in vitro studies in cultured cells, isolated choroid plexus, and isolated membrane vesicles are designed to answer questions about the mechanisms and regulation of taurine transport at the cellular level and to identify molecular mechanisms for transport at each membrane of the choroid plexus epithelium. Two models are proposed for the entry of taurine into the CSF and will be specifically tested. Saturability, specificity, and electrogenicity of taurine transport will be studied in ATP-depleted choroid plexus. Studies in isolated brush border and basolateral membrane vesicles will identify transport mechanisms in each of the polar membranes of the choroid plexus epithelium to determine how the systems may work in concert to mediate transepithelial flux of taurine. Monolayers of cultured choroid plexus cells will be exposed to high and low concentrations of taurine to determine the mechanism of adaptive responses. After elucidating the mechanisms of taurine transport, we will study age- related changes at 4 developmental stages, and if maturational changes are observed, the kinetic mechanism will be identified. Future studies will be directed at elucidating the biochemical events responsible for maturational changes in taurine transport. Defining the mechanism of transport of an amino acid such as taurine via the choroid plexus into the microenvironment of the brain may contribute to effective pharmacologic strategies for a variety of neurologic problems. Furthermore, knowledge of maturational changes in a transport system will contribute to our overall understanding of normal development of the brain.
