|Fixation time||Several hours|
|Acid dyes||Not enhanced|
|Basic dyes||Not enhanced|
How it fixes
Glutaraldehyde cross links proteins in a manner analogous to formaldehyde but targeting different components, such as amino groups. During this process it stabilises the protein mass and preserves the morphology. It fixes somewhat faster than formaldehyde, but its penetration rate is poorer. Since it is extensively used as a primary fixative for electron microscopy it was thought it might function as effectively for light microscopy, but this did not prove to be the case, and it is not popular as a routine fixative.
For histological purposes purified glutaraldehyde should be purchased. It is available as a 25% solution.
Carbohydrates are not fixed, although any protein bound to them will be, i.e. mucins.
Generally, triglycerides remain unfixed but the protein part of lipoprotein may be fixed, and these may resist extraction by solvents.
Morphological preservation is fair to good. The results are similar to formaldehyde.
Glutaraldehyde is usually used alone as a 4% solution, freshly made, in a pH 7.4 buffer. Once made it should be used within 8 hours.
For electron microscopy tiny pieces are fixed quite rapidly, but the 3 mm pieces required for light microscopy require longer. Generally, several hours to overnight will be adequate.
There is no particular aftertreatment for the tissue block, and it may be placed into ethanol at similar concentrations to those used with formaldehyde fixed tissue.
A problem does arise when a staining method is required on sections that depends on the production of aldehydes, such as a PAS or a methenamine silver reduction for fungi etc. Following fixation there are invariably some reactive free aldehyde groups present. These are sufficient in number to interfere with staining techniques which depend on aldehydes to recolour or reduce other solutions.
The resolution to this problem is to carry out an aldehyde block before staining any sections with one of these methods. The aniline-acetic block is suggested as a convenient method that does not take too long. Prior to the oxidation step in the method, block the pre-existing aldehyde by placing a dewaxed and hydrated section into a mixture of 9 parts glacial acetic acid and 1 part aniline for about 30 minutes at room temperature. Then wash well and continue with the oxidation step of the technique.
Culling, C.F.A., (1999)
Handbook of histopathological and histochemical techniques, 3rd ed.
Butterworths, London. pp. 38 - 39
Kiernan. J.A., (1999)
Histological and histochemical methods: Theory and practice, 3rd ed.
Butterworth Heinemann, Oxford, UK. pp. 23 - 24