OBJECTIVES AND AIMS Brain interstitial fluid (ISF) moves between cells and along fiber tracts and perivascular spaces. Normally, it provides nutrients to cells and removes waste products. However, in pathological conditions, it can carry toxic substances to sites of injury or interfere with brain metabolism. The aims of this proposal are to determine autoradiographically the patterns of transport of molecules of different sizes, to assess the effect of ISF transport of toxic enzymes, such as proteases, on white matter injury, and to analyze the role of the basement membrane in blood-brain barrier integrity. These studies are aimed at understanding the nonimmunological mechanisms or demyelination. The effect of free radical-induced edema on ISF transport and metabolism will be studied autoradiographically and with 1H-NMR in rats and cats. Local injections of a free radical generator will cause injury that should interfere with ISF production. The cellular injury is detectable by in vivo 1H-NMR spectroscopy. These studies are important to help in interpretation of 1H-NMR spectroscopy. Brain edema, which frequently accompanies ischemia, trauma and tumors, leads to permanent tissue damage by mechanisms which are poorly understood, and 1H-NMR provides a new method to follow tissue injury noninvasively in animals and humans. METHODS Adult cats will have ventriculocisternal perfusion with radiolabelled extracellular markers for autoradiography and with proteolytic enzymes for histology. The proteolytic enzyme, plasmin along with a phospholipase, will be used to induce demyelination for analysis of patterns of white matter damage, while heparitinase, pronase and collagenase will be used to determine the role of basement membrane in the blood-brain barrier integrity. Rats injected intracerebrally with free radical generator will be followed by 1H-NMR in vivo, and by autoradiography of radiolabelled extracellular molecules. Proton spectra obtained in vivo and in brain extracts in vitro provide information about lactate, amino acids and lipids. Adult cats will have free radical injection prior to analysis of 1H-NMR in the 1.5 Tesla Sigma System, and spectra will be compared with in vivo and in vitro studies in rats at 7 Tesla.