Further histochemical studies characterizing the lipofuscin component of human neuromelanin.

The residuum of bleached substantia nigra neuromelanin and the nonoxidized and oxidized intraneuronal masses of inferior olive lipofuscin gave sudanophilic staining reactions with oil red O, Sudan black B, and a Sudan III and IV combination stain. The pigments also exhibited oxidation basophilia, each having been stained by Gomori's paraldehyde fuchsin method after bleaching or oxidation with potassium permanganate and by the modified carbol fuchsin method of Barbeito-Lopez after bleaching or oxidation with hydrogen peroxide or potassium permanganate. Confirmation of the presence of lipid substances in bleached neuromelanin was obtained by repeatedly staining, decolorizing, and restaining the residuum of the pigment when utilizing the chemically nonreactive beta naphthol type Sudan combination stain, Sudan III and IV. Not only were tinctorial properties characteristic of lipofuscin clearly demonstrated in the bleached residuum of neuromelanin, but additionally, a partial separation was achieved between the relatively soluble beta naphthol type Sudan-staining lipid component and an insoluble component, possibly lipoprotein, staining with Sudan black B and both basic fuchsin dye-containing mixtures. Consideration was given to the idea that the oxidation basophilia of these neuronal pigments was due to the oxidative formation or exposure of one or more kinds of acidic groups consisting of carboxyls or those containing sulfur or phosphorus.