We will determine the regional blood flow response of adult beagles and newborn puppies to graded hypoxia in order to determine whether all regions of the brain have the same sensitivity to hypoxia. The results of the adult and newborn will be compared. Regional cerebral glucose metabolism will also be measured in the adult and newborn animals during various levels of graded hypoxia. This data will aid in determining whether in both the adult and the newborn the pattern of selective vulnerability of the brain can be explained on the basis of a failure of flow to adequately increase to keep pace with the metabolic requirements in some regions. Regional cerebral blood flow and regional cerebral glucose metabolism will both be measured autoradiographically using 123I-iodoantipyrine and 14C-2-deoxyglucose respectively. Both flow and metabolism will be measured simultaneously in each animal utilizing a double label autoradiographic technique we have developed.