The overall goal of this project is to understand how water shifts between extracellular and intracellular compartments during ischemia, and during changes in the brain microenvironment that mimic ischemic events. Basic experiments will be done to choose and characterize an ischemic slice model and to look at related protocols that cause water movement in both normal and gliotic slices. A set of collaborative investigations with other members of the Center will then capitalize on this basic research. During all experiments data will be gathered on light scattering properties of the tissue and [Na] - [K] content to see if they will provide useful indicators of water behavior. Finally the data will be used to model changes in the geometry the extracellular space. The majority of experiments will use slices from the neocortex of rats, with which we have experience under both normal and ischemic conditions. The slice permits the application of different media and drugs at precisely known concentrations. Water compartmentalization will be measured using a combination of the extracellular TAMA-method, based on ion-selective microelectrodes, and the weighing-drying method. Aim 1. After setting up a reliable ischemic slice model we will determine how water moves in the intracellular and extracellular compartments, determine the role of NaCl entry into cells, and assess the role of extracellular calcium. Aim 2. Elucidates which of the changes in the cellular microenvironment that occur during ischemia cause water movements. We shall use the normal slice and elevate [K+]c block Na-K transport, change osmolarity of bathing medium, add glutamate and NMDA and AMPA blockers. Aim 3. Some of the experiments will be repeated on slices containing predominantly glial cells. Aim 4. (With Dr. Margaret Rice ) Studies the distribution of water in the young adult and ag ed guinea pig brain under normal and ischemic conditions both with and without ascorbate in the bathing medium. Aim 5. (With Dr. Mitchell Chesler) Looks at the relationship between the putative Na+ - HCO3 co-transporter and water compartmentalization in the gliotic slice under normal conditions, ischemia and when Na-K transport is blocked. Aim 6. Measures the light scattering properties of the slice and analyzes the total Na and K content for many of the above experiments to determine if these measures permit a simplified approach to charting water movement between compartments. The accumulated data will be used to test models relating volume fraction and tortuosity in the extracellular space.