Localization of tritiated norepinephrine in the renal arteriolar nerves

The innervation of the glomerular arterioles was investigated by light and electron microscopy autoradiography for localization of exogenous tritiated norepinephrine. By light microscopy accumulations of grains were seen associated with afferent arterioles and in lesser numbers with efferent arterioles and neighboring tubules. Accumulations of grains were noted to be in contact with juxtaglomerular granular cells. Electron microscopy autoradiography revealed that nearly two-thirds of the silver grains were on axons. Most of the label was on varicosities packed with small, clear and dense-cored, vesicles. Most varicosities, including those in contact with smooth muscle, juxtaglomerular granular or tubular cells, were labeled. Some varicosities which appeared unlabeled in a given section were labeled in subsequent sections. These findings are consistent with the notion that the glomerular arterioles are innervated mainly by adrenergic nerves. This view is supported by the previously reported observations of the concomitant virtual disappearance of fluorescent and acetylcholinesterase-positive nerves from the region of the glomerular arterioles after two injections of six-hydroxydoapmine (a drug which selectively destroys adrenergic nerves) and the presence of small dense-cored vesicles in all axons of the juxtaglomerular region when examined by serial section electron microscopy.