 The blood-brain barrier BBB is an intricate barrier composed of a variety of efflux pumps, a luminal negative charge, a basal lamina and three distinct cell types: brain endothelial cells, pericytes, and astrocyte foot processes. Specifically, the BBB integrity and degree of permeability is regulated by the capillary endothelial cells in response to astrocytic signals. The strength of intercellular junctions ex. tight junctions, adherins amongst endothelial cells also plays a major role in permeability. Therefore, modulation of all these paracellular properties may decrease BBB integrity and thus improve drug penetration to the tumor bed. Previous studies utilizing the vasoactive peptide, Regadenoson, demonstrated transient increase in BBB permeability, allowing a 70kD dextran molecule to enter the brain of rodents. Thus, the investigators propose to evaluate brain interstitium concentrations of temozolomide pre and post Regadenoson using brain microdialysis. If Regadenoson successfully demonstrates effectiveness in disrupting the BBB, it could be of major importance in improving the outcome of patients with a variety of brain tumors and other neurologic illnesses. 