A Morphological Classification of Retinal Ganglion Cells in the Japanese Catshark Scyliorhinus torazame

Abstract

Retinal ganglion cells (GCs) in the Japanese catshark Scyliorhinus torazame were labeled retrogradely with biotinylated dextran amine (BDA3000). First the labeled cells were classified into 5 morphological types (types I-III: small GCs; types IV and V: large GCs) according to the size of the soma and the dendritic arborization pattern as seen in retinal wholemounts. Type I cells were stellate, with dendrites radiating in different directions. Type II cells had bipolar dendritic trees, with 2 primary dendrites extending in opposite directions. Type III cells had a single thick primary dendrite. Type IV cells were stellate, with dendrites covering a large area centered on the cell body. Type V cells were asymmetric, with most dendrites extending opposite to the axon as a large, fan-shaped dendritic field. Subsequently a wholemount was cross-sectioned, and we classified cells further into multiple subtypes according to the level of dendritic arborization within the inner plexiform layer. The present results suggest the existence of many types of GCs in elasmobranchs in addition to the 3 types of large GCs that have been characterized previously. Some of the newly described GC subtypes in the catshark retina appear to be similar to some of those reported in actinopterygians.

Retinal Morphology and Visual Specializations in Three Species of Chimaeras, the Deep-Sea R. pacifica and C. lignaria, and the Vertical Migrator C. milii (Holocephali)

“…We observed a greater proportion of large ganglion cells than small ganglion cells, which could have been displaced to the inner nuclear or inner plexiform layers [Stell and Witkovsky, 1973;Collin, 1988;Muguruma et al 2014] and therefore not counted. The large ganglion cells may therefore represent a subpopulation of ganglion cells that also have large dendritic fields and be involved in the detection of movement [Barlow, 1953;Boycott and Wässle, 1974].…”

“…Only orthotopic ganglion cells located in the ganglion cell layer were analyzed. In some cartilaginous fishes, a proportion of ganglion cells are located in the inner plexiform and inner nuclear layers of the retina, but these cells are relatively sparsely distrib-DOI: 10.1159/000490655 uted and can be difficult to stain and/or visualized [Muguruma et al, 2014]. So we ignored them in this study, although we recognize that doing so can result in an underestimation of ganglion cell density and thus spatial resolving power (SRP).…”

Structure and diversity of retinal ganglion cells in steller's sculpin Myoxocephalus stelleri tilesius, 1811

“…The successive exclusion of noninformative, redundant, or masking variables resulted in higher‐quality solutions compared to dimensionality reduction using factor analysis. The optimum solutions were based on the dendritic field area and stratification in the retina, functionally relevant parameters used in the vast majority of studies on the structural diversity of GCs (e.g., Doi et al, ; Fletcher et al, ; Muguruma et al, ). The average silhouettes of the optimum solutions were above 0.5, suggesting a strong clustering structure (Gordon, ).…”

The structure and diversity of retinal ganglion cells in the masked greenling Hexagrammos octogrammus Pallas, 1814 (Pisces: Scorpaeniformes: Hexagrammidae)

“…To identify homologous GC types in different vertebrate lineages and reveal the balance between the ancestry and environment ( i.e ., phylogenetic signal) in their structure, function and diversity, systematic studies of these cells in a substantial number of species are required (Freckleton & Rees, 2019). The typological diversity of GCs has been studied in many fish species ( e.g ., Cohen et al ., 2002; Collin, 1989; Hitchcock & Easter, 1986; Mangrum et al ., 2002; Muguruma et al ., 2014). Nonetheless, only a few of these studies meet the aforementioned requirements for objective neuron classification.…”