The section-Golgi impregnation procedure. 1. Description of the method and its combination with histochemistry after intracellular iontophoresis or retrograde transport of horseradish peroxidase.

A method is described for impregnating neurons by the Golgi procedure in sections of brain tissue that are of a thickness 80-100 microns, so allowing a variety of histochemical procedures to be carried out prior to Golgi-impregnation. The method has been applied to the retina of the adult primate and to brain sections incubated to reveal horseradish peroxidase activity with substrates that give electron-dense reaction products. Sections containing neurons that have been filled with horseradish peroxidase by intracellular iontophoresis following electrophysiological characterization, or containing neurons retrogradely labelled by horseradish peroxidase, can be impregnated by this Golgi procedure. Subsequent gold-toning of the Golgi-impregnated neurons makes it possible to study, in the electron-microscope, both Golgi-impregnated and peroxidase-containing neurons and their afferent and efferent synaptic contacts within the same section. The procedure also makes it possible to repeat Golgi impregnation on sections already Golgi-impregnated and gold-toned, or to repeat the Golgi impregnation if the first impregnation is not satisfactory. The procedure is illustrated by examples from the monkey retina, cat visual cortex and rat neostriatum.