Microglia, a specialized type of glia, is related in function and origin to macrophages. While the functional role and properties of brain microglial cells have been debated for some time, recent evidence supports that these cells are tissue resident macrophages. Ramified microglia, a specialized form of microglia, noted for its branching characteristics, appears to be derived from and capable of conversion into active macrophages, however, these cells are inactive in respect to macrophage activity. Because of its inactive status, it has been generally thought that ramified microglia contribute little to the normal operation of brain tissue and serve only as precursors of active macrophages. Previous studies of ramified microglia in tissue culture revealed a combination of motility and pinocytosis, fluid uptake and removal activity. The goal of this research project is to determine the function of ramified microglial. Dr. Thomas will ascertain whether these cells continually take up and exchange fluid for the purpose of removing or degrading small soluble compounds. Experiments utilizing radioactive gamma- aminobutyric acid (3H-GABA) will be performed to determine the kinetic properties of fluid uptake in isolated microglial cells in culture. The kinetic properties will be used to delineate the fluid-phase from the absorptive phase of pinocytosis. In addition, the degradation of pinocytosed compounds will be assessed. Results derived from this investigation will provide information on whether ramified microglia functions as a filtering system to cleanse CNS extracellular fluid.
