Which of the following is a common fixative mentioned for CNS tissue in the material?

• A. Formalin ammonium bromide
• B. Zenker solution
• C. Bouin
• D. Osmium tetroxide

Answer: (A)

Fixing CNS tissue well means locking in delicate neural architecture and preserving lipids and cellular detail so usual stains can reveal structure clearly. Formalin ammonium bromide is a fixative combination that provides good cross-linking with formaldehyde to stabilize proteins, while the bromide component helps tissue penetration and maintains morphology suitable for routine processing and staining of CNS specimens. It’s a commonly referenced option for CNS tissue in standard materials because it balances preservation quality with compatibility with paraffin embedding and downstream stains.

Other fixatives have different trade-offs: Zenker’s solution (a mercuric chloride–based fixative) gives sharp nuclear detail but is hazardous and less favored for general routine use; Bouin’s fixative yields excellent morphology but leaves a strong yellow color and can cause overstaining or tissue handling issues; Osmium tetroxide is excellent for preserving lipids and is routinely used for electron microscopy rather than standard light microscopy of CNS sections.