The fine structure of large dense-core organelles in human locus coeruleus neurons

Protein bodies, the characteristic spherical organelles present in human monoamine neurons, have been shown in previous electron microscope studies to originate as dense bodies in mitochondria. This study was designed to investigate the presence of catecholamine reaction products in the dense bodies of locus coeruleus neurons, in frozen fresh post-mortem brain tissue with the use of potassium permanganate (KMnO4) fixation. This fixation procedure forms a dense KMnO4/catecholamine reaction product, visible in the electron microscope, in the large dense-core vesicles of experimental animals. Our results demonstrate the localization of KMnO4 dense product in the cores of double membrane-bound spherical organelles, as well as in spherical structures in the matrix of typical mitochondria. No typical large dense-core vesicles were observed in these catecholamine neurons of the tissues studied. Our findings are consistent with the notion that altered mitochondria may contribute to the formation of a new type of large dense-core vesicle in the locus coeruleus neurons of man, which is probably an evolutionary adaptation of amine-storing organelles.