Parameters of fixation of the putative pain afferents in the ureter: preservation of the dense cores of the large vesicles in the axonal terminals.

A study has been undertaken of the effects of a number of fixation procedures on the appearance of axons in the ureteric plexuses of the rat, and especially on the appearance of the dense-cored vesicles in those axons which have recently been characterized as pain afferents. Terminals were readily identified in material fixed by perfusion with glutaraldehyde, and many of them contained few if any vesicles. After fixation by immersion in cold glutaraldehyde terminals were not easy to identify because of the loss of microtubules. Immersion fixation in glutaraldehyde produced changes in the number and distribution of the vesicles in the axons which accentuated the similarity of the 'vesicle-containing regions' to the terminals of so-called 'purinergic' axons. Few of the dense-cored vesicles seen in glutaraldehyde-fixed material were preserved by fixation in permanganate, osmium or paraformaldehyde. The way dense-cored vesicles were or were not preserved by the various fixatives used indicated major differences between such cores and those of the vesicles in adrenergic axons. There was also evidence from the study of osmium-fixed material that both the number and appearance of the vesicles can be affected by the type of buffer used: the presence of more vesicles after fixation in osmium buffered with veronal than after osmium buffered in other ways was attributed to the membrane-stabilizing properties of veronal.