Special stains for central nervous system
In the central nervous system, we distinguish the gray substance where are located mainly the cell bodies of neurons and the white matter which is made up of bundles of nerve fibers: axons or cylindraxes, wrapped with Schwann cells.
Neurons are not the only cellular constituents, there are also support cells (the cells of the neuroglia) and blood capillaries.
Two particular types of staining are used to study nervous tissue in the central system: "bichromes" and silver impregnations. "Bichromes", like Dominici, combine a basic dye (toluidine blue) showing basophilic structures (Nissl's body, the nucleus) and an acidic cytoplasmic dye. The absence of connective tissue in the central nervous system renders the use of a third dye unnecessary. The techniques of silver impregnation make it possible to overcome the lack of colorability of the cytoplasmic prolongations of the nerve cells by revealing the cytoskeleton (neurofibrils) which is particularly abundant in these extensions.