Histochemical

Histochemical refers to the field and methods of histochemistry, the study of chemical components and activities within cells and tissues using chemical reactions that yield detectable signals. The goal is to localize, identify, and sometimes quantify specific substances in their native tissue context.

Common approaches include enzyme histochemistry, histochemical staining, and immunohistochemistry. Enzyme histochemistry detects enzymatic activity in situ by providing substrates that produce colored or insoluble reaction products where the enzyme is active. Examples include peroxidase-based detection using diaminobenzidine and alkaline phosphatase substrates. Histochemical stains such as the Periodic Acid–Schiff (PAS) reaction identify carbohydrates and mucopolysaccharides; the Feulgen reaction identifies DNA; and histochemical tests for lipids, glycogen, or other cellular components rely on targeted chemical reactions. Immunohistochemistry, often considered part of histochemistry, uses antibodies to localize specific antigens, typically visualized with enzyme or fluorescent labels.

Procedures typically begin with tissue fixation, processing, and embedding, followed by sectioning and the application of reagents under controlled conditions and appropriate controls. The resulting signals are observed by light or fluorescence microscopy. Important considerations include fixation type, antigen preservation, specificity of reagents, and avoidance of artifacts.

Applications span pathology, neuroscience, developmental biology, and basic research, enabling localization of enzymes, metabolites, and specific biomolecules within tissue architecture. Histochemical techniques remain valuable for correlating structure with biochemical function and for diagnostic and research purposes, often complementing molecular and immunological methods.