Double antigen localization of two catecholamine enzymes and GABA in amacrine cells of the rat retina in semi-thin sections

A double immunohistochemical labeling technique was developed with two immunoperoxidase reactions performed before and after embedding in epoxy resin using two different chromogens: diaminobenzidine (yellowish brown color) and diaminobenzidine + nickel ammonium sulfate (black color).