Electron-microscopic autoradiography of rat hypothalamus after intraventricular h3-norepinephrine.

Tritiated norepinephrine was injected into the lateral ventricles of rats, and its localization in the hypothalamus was determined by light and electron-microscopic autoradiography. Eighty percent of the autoradiographic grains were located over nerve endings and unmyelinated axons. Large, dense synaptic vesicles were present in most of the endings and axons with activity. Grains were rarely seen over myelinated axons, glia, or blood vessels.