Morphology of retinal ganglion cells in lungless salamanders (Fam. Plethodontidae): An HRP and Golgi study

Publisher Website
Google Scholar
Abstract
The family Plethodontidae consists of nearly two‐thirds of all living urodeles; most of them possess highly developed visual abilities. We investigated the morphology of retinal ganglion cells (RGCs) in four representative species by means of the horseradish peroxidase method in flatmounts and in transverse sections and with the Golgi method in transverse sections. In flatmount preparations, four classes of RGCs were found, differing in dendritic arborization, dendritic field size, and stratification pattern of dendrites in the inner plexiform layer (IPL). Class‐1 cells had small dendritic fields (29–44 μm2) and arborized throughout the entire depth of the IPL. Class‐2 cells had medium to large dendritic fields (75–206 μm2) and mostly arborized in two or three laminae or in a diffuse fashion in the IPL. Class‐3 cells had medium to large dendritic fields (72–200 μm2) but sparse dendritic arborization. They only arborized in the proximal lamina of the IPL. Class‐4 cells had large dendritic fields (273–626 μm2) and branched in the most sclerad stratum of the IPL. No large differences in intraspecific soma size of the different RGC classes were detected (although interspecific soma size varied to a considerable degree) and no “giant” cells typically found in other vertebrate retinas were present.The results suggest that, with respect to the pattern of arborization and stratification of dendrites, lungless salamanders possess morphological classes of RGC similar to those found in frogs, but the morphology of RGCs in lungless salamanders seems to be simplified in comparison to frog RGCs. This simplification might be a consequence of paedomorphosis.