Research proposed in this application is directed toward defining the effects of brain blood flow on cerebrospinal fluid formation, composition and reabsorption which are brought about by barbiturate anesthesia, exposure to hypoxic-hypercapnic gas mixtures and under the conditions of changing local brain temperature and whole body hypothermia. Using a technique of perfusing the brain's ventricles with an artifical cerebrospinal fluid which contains radioactively labelled tracers will allow the direct measurement of both active and passive transport of test molecules and ions among the brain's extracellular compartments (its blood, interstitial and cerebrospinal fluids), as well as the calculation of their respective permeability coefficients at their interfaces in response to experimentally adjusted, warm-blooded species (the rabbit) and on an anesthetized poikilotherm (the turtle) to provide comparative physiological data which will describe in more complete detail the interactions of brain blood flow on cerebrospinal fluid dynamics. Since a precise method for the measurement of regional blood flow in the brain and choroid plexus is essential in these tests, support is also requested to allow the further development of a technique which measures local perfusion of a tissue based on its directly assessed thermodynamic properties as shown in the calculations of its thermal conductivity coefficient and facilitated heat transfer due to local blood flow. These are interpreted to indicate blood flow through an analysis of the tissue's conductive, convective, radiative and evaporative heat fluxes and the heat transfer properties of the perfusing blood. Coincident with the development of this technique, the use of injected, radioactively labelled microspheres as a more standard measure will serve as an interim indicator of blood flow for the entire brain, its major anatomical parts and specifically for the choroid plexus.