What is a Fixative?
A
fixative is a chemical substance used in histology to preserve biological tissues. It stabilizes the structure and composition of the tissue, preventing decay and
autolysis (self-digestion) by inactivating enzymes. Common fixatives include formaldehyde, glutaraldehyde, and ethanol.
Why is the Choice of Fixative Important?
The choice of fixative is crucial because it affects the preservation quality of the tissue. Different fixatives have specific properties that make them suitable for various types of tissues and analyses. An incorrect fixative can lead to
artifacts, poor tissue preservation, and unreliable results.
What Happens When an Incorrect Fixative is Used?
Using an incorrect fixative can result in several issues:
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Poor Morphological Preservation: The tissue may shrink, swell, or become distorted.
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Loss of Antigenicity: Some fixatives can mask or destroy antigens, making it difficult to perform
immunohistochemistry.
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Degradation of Ultrastructure: Fine cellular details observed under an electron microscope may be lost.
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Altered Chemical Composition: The fixation process might alter or remove biochemical constituents of the tissue.
Examples of Incorrect Fixative Use
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Using Ethanol for Electron Microscopy: Ethanol is a good fixative for preserving nucleic acids but not suitable for electron microscopy, as it doesn't preserve the ultrastructure well.
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Using Formaldehyde for Enzyme Histochemistry: Formaldehyde can inactivate enzymes, making it unsuitable for
enzyme histochemistry studies.
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Using Glutaraldehyde for Routine Light Microscopy: While glutaraldehyde is excellent for electron microscopy, it can cause excessive cross-linking that hinders staining in light microscopy.
How to Avoid Using the Incorrect Fixative?
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Understand the Tissue Type: Different tissues may require different fixatives. For example, nervous tissue often requires stronger cross-linking fixatives like glutaraldehyde.
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Know the Downstream Application: Choose a fixative based on the intended downstream analysis, such as light microscopy, electron microscopy, or
molecular studies.
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Consult Protocols and Literature: Refer to established protocols or consult scientific literature to identify the appropriate fixative for your study.
Corrective Measures if an Incorrect Fixative is Used
If an incorrect fixative has been used, some corrective measures include:
- Re-Fixation: In some cases, re-fixing the tissue with an appropriate fixative may help, although this is not always effective.
- Optimized Staining Protocols: Modify staining protocols to account for the effects of the incorrect fixative.
- Repeat the Procedure: Although time-consuming, repeating the procedure with the correct fixative is often the best approach to ensure reliable results.Conclusion
The use of an incorrect fixative in histology can severely compromise the integrity and reliability of tissue analysis. Understanding the properties of different fixatives and their suitability for various tissues and applications is critical. Always consult established protocols and scientific literature to select the appropriate fixative, and be prepared to take corrective measures if an error occurs.
