The beaded form of myelinated nerve fibers.
When the nerves are lightly stretched and fixed by freeze-substitution, their fibers show the form-change termed "beading" which consists of a series of undulating constrictions and swellings in the internodes. This form change has not ordinarily been seen in chemically fixed nerves, or when it has, it has been ascribed to a pathological change or an artifact. We now report that beading is also retained in normal nerves when, following a light maintained stretch, they are fixed with aldehydes at a temperature close to 0 degrees C. The degree of beading in single fibers teased from the aldehyde fixed nerves was graded and found to be maximal at 0 degrees C, falling off with increased temperature until, at temperatures above 16 degrees C, most fibers showed no beading or a very mild beading. The fibers of nerves cold-fixed at 0 degrees C displayed the characteristics as freeze-substituted fibers, but with a somewhat smaller number of maximally beaded fibers and an 18% reduction in microtubule numbers in the axons. Desheathing or slitting the sheaths of the nerves before cold-fixation increased the probability of retaining beading. Exposure of stretched nerves to the aldehyde fixative at room temperatures for times as short as 3-5 min before they were cold-fixed showed a diminished degree of beading, indicating that aldehydes can have a deleterious effect on the beading mechanism which we hypothesize to be present in the fiber. This action is distinct from the general cross-linking action of aldehydes.
Department of Physiology, Indiana University School of Medicine, Indianapolis 46202.
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Ochs
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Jersild
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Pourmand
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Potter
D000818:Animals; D016477:Artifacts; D003432:Cross-Linking Reagents / Q000494:pharmacology; D003599:Cytoskeleton / Q000648:ultrastructure; D005404:Fixatives / Q000494:pharmacology; D005557:Formaldehyde / Q000494:pharmacology; D017110:Freeze Substitution; D005976:Glutaral / Q000494:pharmacology; D008297:Male; D009186:Myelin Sheath / Q000187:drug effects / Q000648:ultrastructure; D009413:Nerve Fibers, Myelinated / Q000187:drug effects / Q000648:ultrastructure*; D011108:Polymers / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000648:ultrastructure; D013314:Stress, Mechanical; D016707:Tissue Fixation / Q000379:methods
D003432:Cross-Linking Reagents; D005404:Fixatives; D011108:Polymers; D005557:Formaldehyde; D005976:Glutaral; C003043:paraform