How Does Fontana Masson Staining Work?
The Fontana Masson method relies on the ability of melanin and other argentaffin substances to reduce ammoniacal silver nitrate to metallic silver without the need for an external reducing agent. This reaction results in the deposition of metallic silver, which appears as black or dark brown deposits in the tissue. The process involves treating the tissue sections with silver nitrate solution, followed by washing, and then toning with gold chloride to enhance the contrast.
What are the Limitations of Fontana Masson Staining?
Despite its usefulness, the Fontana Masson technique has limitations. It may not distinguish between different types of pigments, such as melanin and
lipofuscin. Additionally, the staining intensity can be variable, depending on the tissue fixation and processing methods used. In some cases, non-specific staining may also occur, leading to potential misinterpretation.
Fixation: Tissue samples are fixed in an appropriate fixative, such as formalin.
Sectioning: The fixed tissues are embedded in paraffin and sectioned at a thickness of 4-5 micrometers.
Deparaffinization and Hydration: Paraffin sections are deparaffinized in xylene and hydrated through graded alcohols to water.
Silver Nitrate Treatment: Sections are treated with ammoniacal silver nitrate solution, which reacts with melanin and argentaffin substances.
Gold Chloride Toning: The sections are then treated with gold chloride to enhance the visibility of the silver deposits.
Counterstaining: A counterstain, such as nuclear fast red, may be used to provide contrast.
Dehydration and Mounting: The sections are dehydrated through graded alcohols, cleared in xylene, and mounted with a coverslip.
What are the Expected Results?
In Fontana Masson staining, melanin and argentaffin granules appear as black or dark brown deposits, providing a clear contrast against the background tissue. The counterstain helps to highlight the cellular and tissue architecture, making it easier to identify the specific locations of the stained substances.
Conclusion
The Fontana Masson staining technique is a valuable tool in histology for identifying melanin and other argentaffin substances. Its application extends to various fields, including dermatology, oncology, and endocrinology. Despite its limitations, it remains a widely used and effective method for studying pigment-related pathologies and neuroendocrine tissues.
