necessary to discuss the various tools that are available. Many of the histological techniques used to study other tissues can be applied to the nervous system as well. However, there are some techniques that have been developed especially for the study of neuroanatomy. Cell staining In biological systems, staining is a technique used to enhance the contrast of particular features in microscopic images. Nissl staining uses aniline basic dyes to intensely stain the acidic polyribosomes in the rough endoplasmic reticulum, which is abundant in neurons. This allows researchers to distinguish between different cell types (such as neurons and glia), and neuronal shapes and sizes, in various regions of the nervous system cytoarchitecture. The classic Golgi stain uses potassium dichromate and silver nitrate to fill selectively with a silver chromate precipitate a few neural cells (neurons or glia, but in principle, any cells can react similarly). This so-called silver chromate impregnation procedure stains entirely or partially the cell bodies and neurites of some neurons -dendrites, axon- in brown and black, allowing researchers to trace their paths up to their thinnest terminal branches in a slice of nervous tissue, thanks to the transparency consequent to the lack of staining in the majority of surrounding cells. Modernly, Golgi-impregnated material has been adapted for electron-microscopic visualization of the unstained elements surrounding the stained processes and cell bodies, thus adding further resolutive power. Histochemistry Histochemistry uses knowledge about biochemical reaction properties of the chemical constituents of the brain (including notably enzymes) to apply selective methods of reaction to visualize where they occur in the brain and any functional or pathological changes. This applies importantly to molecules related to neurotransmitter production and metabolism, but applies likewise in many other directions chemoarchitecture, or chemical neuroanatomy. Immunocytochemistry is a special case of histochemistry that uses selective antibodies against a variety of chemical epitopes of the nervous system to selectively stain particular cell types, axonal fascicles, neuropiles, glial processes or blood vessels, or specific intracytoplasmic or intranuclear proteins and other immunogenetic molecules, e.g., neurotransmitters. Immunoreacted transcription factor proteins reveal genomic readout in terms of translated protein. This immensely increases the capacity of researchers to distinguish between different cell types (such as neurons and glia) in various regions of the nervous system. In situ hybridization uses synthetic RNA probes that attach (hybridize) selectively to complementary mRNA transcripts of DNA exons in the cytoplasm, to visualize genomic readout, that is, distinguish