Nerve cells, or neurones, in the brain contain some RNA. This often appears to be in stripes, so an older name for it was tigroid, named after tigers, who have stripes (tigroid meaning tiger like). It is now more likely to be referred to as Nissl substance or Nissl bodies, or simply as Nissl, as it is named after a physician with that surname.
Nissl bodies contain significant amounts of RNA and this can be used to demonstrate them, such as with Einarsen's method. Most staining methods which are used for nucleic acids will be successful including the methods for plasma cells, whose selective demonstration also depends on the presence of large amounts of RNA in the cell cytoplasm. In fact, the Unna-Pappenheim type methods stain Nissl bodies quite well. Nevertheless, they are not the most popular for doing so, and methods have been devised which demonstrate them clearly in good contrast to the rest of the brain tissue. These methods are very often used to give an overall view of the neurone content and distribution in sections of brain and spinal cord, rather than because of an interest in the Nissl bodies themselves. Since Nissl is confined to neurones, staining Nissl is tantamount to staining neurones, and it is this which makes its demonstration useful.
The original fixation method recommended was alcoholic. It has been suggested that this may have given sharper staining results due to removal of some cellular lipid which obscured the staining. It is recommended that frozen sections should be treated with ethanol and xylene to remove some of the lipids before staining. Formalin fixed paraffin sections will have this done during processing, but further treatment may still improve staining.
Thin sections are not usually of any benefit for staining Nissl and it is usually recommended that sections be thicker than normal, about 10 μmetres or thicker for paraffin sections, to give a sufficient depth of colour.
Most staining methods follow Nissl's original example and use blue, basic dyes to overstain the Nissl bodies, then remove excess dye by differentiating in a fluid which dissolves it out of the section, usually ethanol (95%), often with some cajeput oil or acetic acid.. In a well stained preparation the Nissl bodies are darkly stained, outlining nerve cells clearly against a pale background. Nuclei of all cells, being predominantly nucleic acid, will also be stained. Most of these methods are satisfactory. For paraffin sections the cresyl violet method differentiated with 95% ethanol acidulated with acetic acid will generally be found to be convenient and easily controlled.
|Einarsen's gallocyanin-chrome alum|
|Nissl's methylene blue|
|Nissl bodies||Neurone||Spinal cord|
Drury, R A, and Wallington, E A, (1967).
Carleton's histological technique., Ed. 5., pp. 379.
Oxford University Press, London, England.
Last updated March 2016.