PRESERVATION OF MYELINATED FIBERS FOR ELECTRON-MICROSCOPY - A QUALITATIVE COMPARISON OF ALDEHYDE FIXATION, MICROWAVE STABILIZATION AND OTHER PROCEDURES ALL COMPLETED BY OSMICATION

A qualitative comparison was made of a variety of electron microscopic preservation methods for nervous tissue, especially with respect to m yelinated fiber areas. The methods studied were aldehyde perfusion/imm ersion fixation, aldehyde-tannic acid immersion fixation (stimulated b y either microwave or conventional heating), microwave stabilisation, saline treatment with conventional heating (all with secondary osmicat ion), and primary osmication. For all methods three morphological aspe cts, the ultrastructural quality of myelin sheath and axon and the coh erence between the two were judged separately. It appears that the bes t version of each method studied is capable of providing a good overal l ultrastructural result but always shows a preference for one or two of the three separate morphological aspects. When aiming at good axon quality together with good axon/myelin coherence, aldehyde perfusion/i mmersion, saline treatment or primary osmication are almost equivalent . Microwave stabilisation, on the other hand, can be chosen when good myelin quality has to be combined with good axon quality. For more spe cific purposes the following examples can be given. When excellent mye lin quality is needed both microwave-stimulated aldehyde-tannic acid f ixation or microwave stabilisation can be considered. When the preserv ation of the axon quality has priority the aldehyde-perfused tissue sh ould be further immersed in a heated aldehyde-tannic acid solution. Pr imary osmication guarantees excellent axon/myelin coherence. Despite t he differences in detail, a remarkable correspondence is stressed betw een the overall results of sometimes extremely different methods of ti ssue preservation. Probably they all guarantee a reliable reflection o f the in vivo situation. With respect to the use of microwave irradiat ion for tissue preservation, it appeared that stabilisation procedures are rather capricious. However, if successful, the results are not in ferior to those of aldehyde fixation.