Retinal Ganglion Cell Distribution and Spatial Resolving Power in the Japanese CatsharkScyliorhinus torazame

Abstract

Topographic distribution of retinal ganglion cells (GCs) is linked with the visual capabilities and behavioral ecology of vertebrates. Studies on the distribution of different types of GCs, however, have been conducted in only a few species of elasmobranchs. In the present study, the distribution and peak cell density of GCs, and spatial resolving power (SRP) were examined in the Japanese catshark, Scyliorhinus torazame. Distinct populations of GCs were identified in the ganglion cell layer of S. torazame based on soma size: small and large GCs, which showed different spatial distribution patterns. A horizontal streak of high cell density was recognized in the dorsal retina for small GCs. The highest cell density occurred within the streak, and the peak SRPs of the three fish investigated in the present study were 2.32, 2.64, and 3.01 cycles/deg. In contrast, two spots of high cell density, or areae gigantocellulares, were identified for large GCs, one in the temporal and the other in the nasal retina. The highest cell density occurred in the temporal or nasal area gigantocellularis (SRP: 1.36, 1.55 and 1.83 cycles/deg). This is the first study reporting an elasmobranch species with a horizontal visual streak of small GCs and two areae gigantocellulares. The horizontal streak of small GCs in the dorsal retina, which serves for the inferior visual field, is likely important for food search on the bottom, and the areae gigantocellulares may be important to the detection of prey and/or predators approaching from the front or behind the catshark.

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

“…It grows to a maximum length of 50 cm and is easy to keep in the laboratory; therefore it is useful for experimental studies. We recently published an initial study of the retina of this shark, which revealed the existence of large and small GCs [Muguruma et al, 2013]. The present, more detailed study will serve as the basis for future experimental studies on the visual system of this species, and those studies are expected to reveal that different subtypes of GCs project to different central targets and mediate distinct functions in cartilaginous fishes, as in other vertebrates including mammals [Rodieck and Watanabe, 1993].…”

“…A number of studies have reported that there are populations of small and large GCs in elasmobranch (sharks and rays) retinas [Peterson and Rowe, 1980;Bozzano and Collin, 2000;Bozzano, 2004;Lisney and Collin, 2008;Litherland and Collin, 2008;Litherland et al, 2009;Muguruma et al, 2013]. However, only 3 types of large GCs with different soma and dendritic morphologies have been identified so far [Stell and Witkovsky, 1973] in these retinas.…”

“…More recently, a number of studies using Nissl staining revealed the presence of small and large GC somas in various cartilaginous fishes [Peterson and Rowe, 1980;Bozzano and Collin, 2000;Bozzano, 2004;Lisney and Collin, 2008;Litherland and Collin, 2008;Litherland et al, 2009;Muguruma et al, 2013]. However, the Nisslstained small GCs could not be classified further (except possibly for those described in the giant shovelnose ray [Collin, 1988]; see Introduction) because the Nissl stain does not usually delineate dendritic structures.…”

“…All three of these studies noted the presence of small as well as large GCs but did not classify them further. A number of later studies also revealed small and large GCs in cartilaginous fishes [Peterson and Rowe, 1980;Collin, 1988;Bozzano and Collin, 2000;Bozzano, 2004;Lisney and Collin, 2008;Litherland and Collin, 2008;Litherland et al, 2009;Muguruma et al, 2013] but again without further classification. An exception is a study in the giant shovelnose ray where three populations of GCs with different soma sizes and depths were described [Collin, 1988], and the smaller of the two may represent different subpopulations of small cells.…”

Visual Capability of the Weakly Electric Fish <b><i>Apteronotus albifrons</i></b> as Revealed by a Modified Retinal Flat-Mount Method

“…Several methods of retinal flat-mount preparations to examine the topographic distribution of neuronal elements in retinae have been developed [for a review, see Collin, 2008;Ullmann et al, 2012]. Surgical removal [Graydon and Giorgi, 1984;Collin and Pettigrew, 1988;Mangrum et al, 2002;Ullmann et al, 2012;Muguruma et al, 2013] or chemical bleaching [Oliveira et al, 2006;Ullmann et al, 2012] of the pigment epithelium is usually required for observation with a conventional microscope using transmitted light [Ullmann et al, 2012].…”