Studies to improve fixation of human nerves. V. Effect of temperature, fixative and CaCl2 on density of microtubules and neurofilaments.

Utilizing morphometry of electron micrographs of nerves of rat fixed with different schedules of fixation it was concluded that: irrespective of the fixative, fixation at low temperature is associated with markedly low densities of microtubules (MT) of myelinated and of unmyelinated fibers; of the various fixatives tested 2% glutaraldehyde in 0.1 M cacodylate buffer without 0.025 M CaCl2 was associated with the highest density of MT of myelinated fibers and the addition of 0.025 M CaCl2 to a 2% glutaraldehyde fixative solution is associated with abnormally low densities of MT in myelinated and unmyelinated fibers. An effect of temperature, fixative and added CaCl2 on neurofilaments density was not demonstrated. Using the criterion of density of MT and assuming that these studies on rat nerves can be applied to biopsied nerve of man, fixation of human nerves should be at room or body temperature, and the fixative solution should not contain 0.025 M CaCl2.