Retinal growth in foveated teleosts: nasotemporal asymmetry keeps the fovea in temporal retina

Abstract

Fish retinas continue to grow throughout life by adding neurons at the margin, with the result that cells born at a peripheral site are steadily displaced toward the center of the enlarging retina. This presents a functional problem for fish with specialized temporal areas such as a fovea--how to reconcile continual growth with the maintenance of a temporal location for the fovea. One possibility is that the retina grows asymmetrically, with most new retina added nasally, relatively little temporally. I have tested this hypothesis by evaluating retinal growth in marine teleosts from 15 families, both foveated and unfoveated. The pattern of growth was revealed by exploiting the fact that each new generation of ganglion cells sends its axons into the optic nerve as a cohort; small grains of the carbocyanine dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethyl- indocarbocyanine were applied to various sites in the cross section of the optic nerves of adults, and the retrogradely labeled cell bodies in the retina were visualized in whole-mounts. The labeled cells lay in annuli, each one a generation of ganglion cells. Representatives of seven of the families showed clearly asymmetric growth: the labeled annuli were close together on the temporal side and more distant nasally, the embryonic fissure curved from its ventral origin toward the temporal side, and in six of these families, labeled fibers from temporal retina skirted the fovea. Members of the other eight families, without specialized areas, had more symmetric retinal growth: labeled annuli were equally spaced on all sides, the embryonic fissure was vertical, and there were no skirting fibers. The following hypothesis is supported: the retina grows asymmetrically, and maintains the area for acute vision oriented toward the anterior field.

Cone photoreceptor regeneration in adult fish retina: phenotypic determination and mosaic pattern formation

“…The resulting eye cups were fixed by immersion in 4% paraformaldehyde in 0.05 M PO, buffer overnight. One or more small pellets of the fluorescent carbocyanine dye DiI (l,l'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate;Molecular Probes, Eugene, OR;Honig and Hume, 1986;Godement et al, 1987) were embedded within the cut face of the optic nerve (n = 13), and the eye cups were incubated in fixative at 45°C for 5 d. DiI was incoruorated into retinal aanelion cell (RGC) axonal membranes local to the pellet, and retrogGde?y labeled annuli of RGC somata and dendrites (Easter, 1992;Cameron and Easter, 1993), and one of these annuli generally intersected the lesion site or lay peripheral to it. Retinal whole-mounts were made with the pigment epithelium side down, cover slipped with 50% glycerol, 50% PO, buffer, and viewed with epifluorescence microscopy.…”

Control of Cellular Pattern Formation in the Vertebrate Inner Retina by Homotypic Regulation of Cell-Fate Decisions

“…Specifically, PCNA-positive cells were located at the extreme margin of all retinas (Fig. 1 A), corresponding to the location of the CGZ (Johns, 1977;Easter, 1992;Cameron 1995). BrdU incorporation was also observed in this location (Fig.…”

Enhancing videoconferencing using spatially varying sensing

“…Studies have shown that animate vision has much higher resolution in the center of the visual field than in the periphery [9], [13], [14], [16], [20], [21], [23], [31], [32]. Several mathematical models and vision systems have been developed based on this variable resolution concept [4], [6], [24], [26], [28], [33].…”

“…We can define an iteration step which will converge to the zero crossing (16) Now, for every angle relative to a fovea we have to provide and , and use the iteration procedure to numerically compute and .…”