The objective of this project is to determine the functional relationships between individual CNS vasomoter control systems (commonly called vasomoter "centers" or vasomoter "pathways"). This objective constitutes a necessary sequel to the extensive studies which have identified and characterized individual vasomotor mechanisms in detail. The proposed study recognizes that vasomotor mechanisms do not act separately and that physiological interactions between central vasomotor mechanisms cannot be predicted by linear combinations of their individual effects. This study will provide two levels of information. The first level will consist of empirical data which will provide immediate (if not generalizable) insight into the types of vasomotor interactions which occur and their relative importance in various vascular beds. In these experiments, vasomotor systems will be electrically excited, first individually and then simultaneously. Vasomotor output will be assessed by measuring arterial and venous pressures, cardiac output and regional blood flows in skeletal muscle, mesenteric and renal vascular beds. The second level of information will characterize the mechanisms of interaction between vasomotor systems and will develop a comprehensive view of vasomotor control which will permit accurate predictions of complex autonomic behavior. The loci and modes of interaction will be determined by combining the techniques of simultaneous stimulation with focal lesions, careful neuroanatomical mapping, pharmacological blockade and direct microscopic observation of the peripheral vasculature.