Localization of uptake of tritiated norepinephrine by rat brain <i>in vivo</i> and <i>in vitro</i> using electron microscopic autoradiography

Abstract

Abstract Previous studies have identified granular vesicles in peripheral adrenergic axons, and larger granular vesicles in various brain regions which seem to be correlated with the presence of norepinephrine. In the present study, electron microscopic autoradiography was used to localize 3 H‐norepinephrine taken up by brain slices in vitro and by brain in vivo after injection via the lateral ventricle. In both preparations, the label was found predominantly in relation to small, unmyelinated axons and nerve endings. Many of these contained granular vesicles in axons which were located in regions of the brain known to contain norepinephrine. It is suggested on the basis of this study and previous work, that exogenous norepinephrine is accumulated by brain axons and nerve endings which contain endogenous norepinephrine, and that the presence of granular vesicles is a common feature of such structures.