Density, proportion, and dendritic coverage of retinal ganglion cells of the common marmoset (Callithrix jacchus jacchus)

F.L Gomes,C.A Saito,E.S Yamada,L.C.L Silveira

doi:10.1590/s0100-879x2005000600014

Abstract

We performed a quantitative analysis of M and P cell mosaics of the common-marmoset retina. Ganglion cells were labeled retrogradely from optic nerve deposits of Biocytin. The labeling was visualized using horseradish peroxidase (HRP) histochemistry and 3-3'diaminobenzidine as chromogen. M and P cells were morphologically similar to those found in Old- and New-World primates. Measurements were performed on well-stained cells from 4 retinas of different animals. We analyzed separate mosaics for inner and outer M and P cells at increasing distances from the fovea (2.5-9 mm of eccentricity) to estimate cell density, proportion, and dendritic coverage. M cell density decreased towards the retinal periphery in all quadrants. M cell density was higher in the nasal quadrant than in other retinal regions at similar eccentricities, reaching about 740 cells/mm(2) at 2.5 mm of temporal eccentricity, and representing 8-14% of all ganglion cells. P cell density increased from peripheral to more central regions, reaching about 5540 cells/mm(2) at 2.5 mm of temporal eccentricity. P cells represented a smaller proportion of all ganglion cells in the nasal quadrant than in other quadrants, and their numbers increased towards central retinal regions. The M cell coverage factor ranged from 5 to 12 and the P cell coverage factor ranged from 1 to 3 in the nasal quadrant and from 5 to 12 in the other quadrants. These results show that central and peripheral retinal regions differ in terms of cell class proportions and dendritic coverage, and their properties do not result from simply scaling down cell density. Therefore, differences in functional properties between central and peripheral vision should take these distinct regional retinal characteristics into account.

Highlights

In order to understand how the image is sampled at the earliest stages of visual information processing, it is important to know how different ganglion cell classes are distributed throughout the retina
Dacey and Petersen (5) and Dacey (6) suggested that the coverage factor remains constant with eccentricity in the human and macaque retina because the increase of the dendritic field size is counterbalanced by a proportional decrease of cell density
Cell morphology was quantified by measuring a sample of 182 M cells and 839 P cells

Summary

Introduction

In order to understand how the image is sampled at the earliest stages of visual information processing, it is important to know how different ganglion cell classes are distributed throughout the retina. There are indications that the P/M density ratio remains fairly constant in the central retina, but changes towards the nasal periphery (4-7). We know that in some species M cells represent 5 to 10% of all ganglion cells in the central retina, but that this proportion increases towards the nasal periphery (8,9). Another important measurement for morphologic studies of the retina is the coverage factor, which was introduced by Perry and colleagues (4) to quantify how many cells of a single type cover each retinal location. Perry et al (4) for the macaque monkey retina and Yamada et al (7) for the capuchin monkey retina, showed that the M and P cell coverage factor changes as a function of eccentricity

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Results

Conclusion