Retinal ganglion cells that project to the dorsal lateral geniculate nucleus in the macaque monkey

Perry, V.H., Oehler, R. and Cowey, A. (1984) Retinal ganglion cells that project to the dorsal lateral geniculate nucleus in the macaque monkey. Neuroscience, 12 (4), 1101-1123. (doi:10.1016/0306-4522(84)90006-X).

Abstract

Horseradish peroxidase was deposited in the optic nerve to retrogradely label and reveal the dendritic form of all classes of ganglion cell, or it was injected into the dorsal lateral geniculate nucleus to reveal only those classes projecting to the thalamus. The results were compared with those of the accompanying paper in which the ganglion cells projecting to the midbrain are selectively revealed. Two major classes of ganglion cells are described, the Pα and Pβ cells. For both classes dendritic field size increases with eccentricity from the fovea and there is no overlap in the two classes at any given eccentricity. Cell body size shows a similar mean difference but with a slight overlap. Both cell bodies and dendritic fields are larger along the temporal horizontal meridian than the nasal horizontal meridian, for Pα and for Pβ cells, but these differences are reduced when naso-temporal differences in ganglion cell density are taken into account, that is, size correlates closely with density. Injections restricted to the parvocellular layers of the lateral geniculate nucleus labelled almost exclusively Pβ cells, whereas injections confined to the magnocellular layers labelled almost exclusively Pα cells. As midbrain injections label no Pβ cells and few Pα cells it can be shown that about 80% of ganglion cells are Pβ cells projecting to parvocellular lateral geniculate nucleus, and that about 10% are Pα cells projecting to magnocellular layers. The coverage factor, that is the number of cells covering each point on the retina, varied from 1.9-2.3 for Pβ cells, and from 2-7 for Pα cells. Comparing the results with those of comparable investigations on cats and rabbits shows a much clearer segregation of the terminal targets of different classes of ganglion cell in monkeys, the greatest difference being the absence in the monkey of a projection to the geniculate from gamma- and epsilon-like cells. Further, axons which branch and innervate both thalamus and midbrain are rare in monkeys but common in other mammals. Comparing the results with those from physiological investigations suggests that the Pβ cells correspond to colour-opponent cells, whereas Pα cells correspond to the achromatic broad-band magnocellular cells.

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