Origins of crossed and uncrossed retinal projections in pigmented and albino mice

Abstract

The extent of the binocular cortical field in albino mice, as revealed by recording from single cells, was almost normal; although the input from the ipsilateral eye was weaker than normal, most cells were driven from both eyes. By backfilling retinal ganglion cells from one optic tract with horseradish peroxidase we examined the origins of the retinofugal projections. Filled cells ipsilateral to the injected tract were concentrated in a crescent-shaped area bordering the inferior temperal retina. In black mice this area constituted 20% of the total retinal area, in albinos 17%. In black mice we counted nearly 1,000 labeled cells in the ipsilateral retina, or 2.6% of all cells filled in both eyes. Albinos had about one-third fewer filled cells ipsilaterally than black mice. Four percent of all ipsilaterally filled cells in black mice and 8% in albinos were scattered outside of the crescent region. The density of ipsilaterally projecting cells was uniform throughout the crescent region in black mice, but decreased toward the central retina in albinos. In retinas contralateral to the injection up to 39,000 cells were filled-about two-thirds of the cells in the ganglion-cell layer whose cytoplasm contained conspicuous Nissl substance. Depending on classification of unfilled cells as ganglion cells or interneurons, we estimated a total of 48,000 to 65,000 ganglion cells to exist in the retina. The size distribution of ipsilaterally projecting ganglion cells was similar in albinos and normals. Ipsilaterally projecting ganglion cells were on average 1.8-3 times larger in volume than contralaterally projecting ones in both types of mice. Displaced ganglion cells were relatively more common in ipsilateral retinofugal projections: 21% of all ipsilateral ganglion cells were displaced versus less than 1% of all the contralateral ganglion cells in black mice. In albinos only 13% of the ganglion cells in the ipsilateral retina were displaced. The overall reduction in ipsilaterally projecting cells in albinos was reflected twice as much in displaced ganglion cells as in normally placed ones.

Visual Function in Mice with Photoreceptor Degeneration and Transgenic Expression of Channelrhodopsin 2 in Ganglion Cells

“…When the plane of focus is shifted to the amacrine cell layer a sparse population of cell bodies was labeled (data not shown). We interpret these sparse somas to be displaced ganglion cells (Dräger and Olsen, 1980).…”

“…At an eccentricity of 1-2 mm from the optic disc the density of ChR2-YFP cells was 787 Ϯ 252 (n ϭ 8) cells per mm 2 . Dräger and Olsen (1980) estimated the density of ganglion cells of the mouse that were retrogradely labeled from the optic tract to be 2680 Ϯ 231 (n ϭ 7) per mm 2 , which would confirm that approximately one third of the ganglion cells express ChR2-YFP.…”

Visual thalamocortical circuits in parvalbumin-deficient mice

“…However, the study of the functional properties of the visual pathway of mice has attracted limited attention by the neurophysiologists in the past probably because of the poor visual acuity of this species (Prusky et al, 2000). In mice, less than 3% of the entire retinofugal pathway projects ipsilaterally (Dräger and Olsen, 1980), and the number of retinal ganglion cells viewing a point in binocular space is 9 times smaller for the ipsilateral than for the contralateral retina (Dräger and Olsen, 1980). Despite such disparity in retinofugal projections the contralateral-to-ipsilateral ratio of visually evoked responses is only 2 times smaller for the ipsilateral than for the contralateral retina at the level of the primary visual cortex (Coleman et al, 2009).…”

The Experimental Manipulation of Visual Cortex Efferents

“…In rodents, most of the retinal ganglion axons cross the optic chiasm to the contralateral side [5,6]. Thus, retinal deafferentation is a convenient experimental means of investigating the plastic response mechanisms to central nervous system (CNS) lesions.…”