Chemical reduction of silver chromate: a procedure for electron microscopical analysis of Golgi-impregnated neurons.

A procedure is described by which the solid silver chromate precipitate present in Golgi-impregnated neurons is reduced by a photographic developer into metallic silver grains or particles. The remaining silver chromate is subsequently removed, and the fine structure and synaptic relationships of the impregnated neurons can be studied with the electron microscope. Three developers, Hydrochinone, Kodalith and D 19 were tested on cortical neurons in Vibratome sections of rapid Golgi-impregnated rat brains. Considerable differences were observed as regards penetration of the developer into the sections, uniformity of development, size and location of the silver particles produced during the development, and the quality of preservation of the ultrastructural details both in the impregnated neurons and the surrounding neuropil. Following the chemical reduction procedure the metallic silver deposit can be converted into metallic gold by a gold toning technique. Of the 3 tested developers, Kodalith and D 19 met the demands: good ultrastructural preservation, high contrast at both light microscopic (LM) and electron microscopic (EM) levels, reliable and easy to perform, minimum of test runs. Because of the high contrast provided by Kodalith and D 19, these substances are well suited for neuroanatomical tracing studies which make use of a transport or degeneration technique combined with Golgi-EM. In contrast to Kodalith, D 19 has little effect on the ultrastructure of the impregnated cells. Therefore, this developer can also be used for ultrastructural studies of Golgi-impregnated, light microscopically identified neurons.