Retinal crowding alters the morphology of alpha ganglion cells

It has been hypothesized that the dendritic field size of individual retinal ganglion cells is regulated early in development by interactions among neighboring cells (Wässle and Reiman, Proc. R. Soc. Lond. B. 200:441-461, 1978). An opportunity to test this hypothesis is provided by the consequences of prenatal enucleation that results in an increased density of ganglion cells in the remaining retina (Chalupa et al., Neuroscience 12:1139-1146, 1984). In the present study we compared dendritic field diameters of alpha ganglion cells in normal retinas to those of adult cats that were monocularly enucleated before birth (on embryonic days 42 and 51) and 6 days after birth. In each animal ganglion cells were labeled by central injections of horseradish peroxidase. The retinas were incubated according to a modified Hanker-Yates procedure and whole-mounted. All cells were sampled from the temporal retina along a corridor established by a line drawn through the optic disk and the area centralis. Alpha cells were differentiated into ON and OFF subtypes on the basis of their level of stratification in the inner plexiform layer (Peichl and Wässle, Proc. R. Soc. Lond. B. 212:139-156, 1981). Dendritic field and soma diameters were determined from complete cell drawings by calculating the mean of the two longest orthogonal diameters. Our main findings are: Early monocular enucleation does not disrupt the mosaics of ON and OFF alpha ganglion cells in the remaining retina of adult animals. Within the retinal corridor sampled, the density of alpha cells was substantially greater than normal in the remaining retina of the prenatal enucleates at all eccentricities except the far periphery. Except at the far periphery, the dendritic field diameters of the prenatally enucleated animals were significantly smaller than normal when compared at equivalent eccentricities. However, when compared at equivalent cell densities, dendritic field dimensions in the prenatally enucleated and normal animals were found to be similar. In the prenatal enucleates the somas of these neurons were also significantly smaller than normal. If the monocular enucleation was postnatal, however, the density and the dendritic field diameters of alpha cells did not differ appreciably from normal. These results indicate that the morphology of retinal ganglion cells can be influenced by increasing the density of developing ganglion cells.(ABSTRACT TRUNCATED AT 400 WORDS)