The staining of degeneration in the nervous system of the octopus by modified silver methods

Introduction DEGENERATING axons of cephalopod material can be stained with a Cajal method (Sereni and Young, 1932). Whilst this has proved extremely valuable for demonstrating principal fibre connexions, it becomes more difficult to interpret the results when identifying degenerating fibres which are diffusely distributed within neuropil, or in tracts composed mainly of normal fibres. This is largely because there is no differential staining of degenerating and normal fibres, such as can be found in vertebrate material stained by the Nauta and Gygax method (Nauta and Gygax, 1954). A further difficulty is that degenerating fibres stained by the Cajal method often do not appear as grossly distorted as vertebrate degenerating fibres stained by the Glees method (Glees, 1946) or either Nauta and Gygax method (Nauta and Gygax, 1951, 1954). However, none of these techniques for vertebrates is satisfactory when used on the octopus brain. It has therefore been considered valuable to adapt them for use on such material. A large number of variants have been tried. The two outlined below are found to be the most successful in that they consistently produce reliable results, and stain a maximum amount of degeneration when compared with Cajal-stained material. The preliminary study has been made on Octopus vulgaris in which one optic tract has been cut intracranially. Post-operative survival times of one to six days have been used with a tank temperature of 20 to 25 C.