COMPARISON OF PHOTORECEPTOR SPATIAL DENSITY AND GANGLION-CELL MORPHOLOGY IN THE RETINA OF HUMAN, MACAQUE MONKEY, CAT, AND THE MARMOSET CALLITHRIX-JACCHUS

We studied the relationship between the morphology of ganglion cells a nd the spatial density of photoreceptors in the retina of two Old Worl d primates, human and macaque monkey; the diurnal New World marmoset C allithrix jacchus; and the cat. Ganglion cells in macaque and marmoset were labelled by intracellular injection with Neurobiotin or by DiI d iffusion labelling in fixed tissue. Cone photoreceptor densities were measured from the same retinas. Supplemental data for macaque and data for human and cat were taken from published studies. For the primates studied, the central retina is characterised by a constant numerical convergence of cones to ganglion cells. Midget ganglion cells derive t heir input, via a midget bipolar cell, from a single cone. Parasol cel ls derive their input from 40-140 cones. Outside the central retina, t he convergence increases with eccentricity. The convergence to beta ce lls in the cat retina is very close to that for parasol cells in prima te retina. The convergence of rod photoreceptors to ganglion cells is similar in human, macaque, and marmoset, with parasol cells receiving input from 10-15 times more rods than midget cells. The low convergenc e of cones to midget cells in human and macaque retinas is associated with distinctive dendritic ''clusters'' in midget cells' dendritic fie lds. Convergence in marmoset is higher, and the clusters are absent. W e conclude that the complementary changes in photoreceptor density and ganglion cell morphology should be considered when forming linking hy potheses between dendritic field, receptive field, and psychophysical properties of primate vision. (C) 1996 Wiley-Liss, Inc.