Some of the effects of norepinephrine, an important neurotransmitter, are mediated by beta-adrenergic receptors. These receptors have been identified and partially characterized in rat brain using radioactive antagonists in reversible binding studies. Preliminary investigations indicate large variations in the distribution and properties of beta-receptors in various mammalian species and among various brain regions. I therefore propose to systematically characterize the beta-adrenergic receptors in selected brain regions of several mammalian species by studying the binding of the potent beta-antagonist, 3H-dihydroalprenolol (DHA), to particulate preparations of brain tissue samples. The characterizations will include a determination of the K and B of 3H-DHA binding, the Ki for agonists and antagonists in inhibiting 3H-DHA binding, and the effect of anions and nucleotides on the extent, affinity and kinetics of binding.