Silver Impregnation of Degenerating Axons; Comparisons of Postoperative Intervals, Fixatives and Staining Methods

By introducing variations in procedures and comparing density and patterns of degeneration exhibited, we found that: (1) in the rat, cat, and monkey, the optimum survival time was about 1 wk; this period yielding the maximum amount of argyrophilic reaction and the most consistent staining among several different parts of the brain. Survival times of up to 3 wk did not seriously impair the interpretation of argyrophilial patterns; (2) some qualitative changes in the nuclear patterns of degeneration suggested that the use of a range of survival times may provide useful data; (3) staining differences and similarities in different neural systems of known connections were about the same in the 3 species of animals; (4) formalin, buffered formalin, and a 4%:1% paraformaldehyde-glutaraldehyde mixture were satisfactory perfusion solutions; however, staining was less intense when the Nauta-Gygax method followed the last fixative mixture; (5) The Fink-Heimer I method yielded more consistent results than did the Fink-Heimer II or the Nauta-Gygax methods.