Pioneering a golden age of cerebral microcircuits: the births of the combined Golgi-electron microscope methods.

Theodor W. Blackstad devised methods by which the synaptic connectivity of neuron somata and their dendritic and axonal processes in the CNS could be analyzed by the combined use of light and electron microscope techniques. His first publication on that subject dates from 1965 and was contemporary to the independent research by William K. Stell. The Golgi method was an obvious neuronal marker at those times, and Blackstad and Stell showed that the Golgi precipitate is electron-dense and intracellular and, therefore, it could help identify in the electron microscope, with great accuracy, profiles of neurons initially visualized in light microscopy. Besides this convergent research, Blackstad demonstrated for the first time that anterograde axonal degeneration could be combined with the Golgi-electron microscope method, allowing the identification of the neurons whose dendritic or somatic profiles were postsynaptic to the severed axonal afferent projections. Last, but not least, Blackstad pioneered de-impregnation techniques for electron microscopy of Golgi preparations. This had a great impact in the study of synaptic circuitry. The present account is a remembrance of the events that linked these early attempts with the development of a de-impregnation method based on gold toning by Alan Peters and the present author.