MORPHOLOGICAL EVIDENCE FOR SYMPATHETIC INNERVATION OF BROWN ADIPOSE TISSUE OF RAT - A FLUORESCENCE AND ELECTRON MICROSCOPIC STUDY

Interscapular brown adipose tissue of the rat was examined by means of fluorescence and electron microscopy, in order to provide a conclusive morphological basis for the sympathetic innervation of this adipose tissue. Fluorescence microscopically, we observed scattered fine nerve varicosities between the brown fat cells showing catecholamine [noradrenaline]-specific fluorescence. Such a fluorescence was not observed in brown adipose tissue from reserpinized animals. No fluorescence could be detected in the cytoplasm of brown fat cells. Electron microscopically, after KMnO4 fixation, a number of small granular vesicles (about 500 Å in diameter) were found in the fine non-myelinated axons or preterminals partially covered by Schwann cells in the intercellular space. Occasionally, a small axon terminal containing a number of such granular vesicles was located in a depression on the surface of a brown fat cell. There was then only a cleft of 200 Å and no basement membrane. After treatment of the animals with reserpine, the electron density of granules in the vesicles decreased. From our morphological findings as well as from other physiological and biochemical data, we conclude that brown adipose tissue is innervated by sympathetic nerves. © 1969 Springer-Verlag.