The Cajal staining method uses which fixative?

• A. Formalin ammonium bromide
• B. Neutral buffered formalin
• C. Bouin's solution
• D. Glutaraldehyde

Answer: (A)

In this staining method, the fixative must preserve delicate neuronal structures while creating the chemical environment that allows silver impregnation to occur effectively. Formalin ammonium bromide provides that balance: formaldehyde fixes and preserves tissue by crosslinking proteins, while the ammonium bromide supplies bromide ions that participate in the silver impregnation chemistry, helping form silver compounds that are later reduced to metallic silver during development. This enables clear, complete visualization of neurons and their processes, which is the hallmark of the Cajal staining pattern. Other fixatives either over-fix tissue or alter the chemical milieu in ways that hinder the selective deposition of silver on neurons, making them less suitable for this method.