Development of catecholaminergic, indoleamine-accumulating and NADPH-diaphorase amacrine cells in rabbit retinae

We have investigated the ontogeny of four classes of amacrine cells in the rabbit retina. In particular, the distribution, number, soma diameter, dendritic field diameter, and pattern of dendritic stratification were studied in catecholaminergic (CA) and indoleamine-accumulating (IA) amacrines and in two classes of nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase amacrine cells. The first CA and IA cells are observed on the 27th postconceptional day (27PCD) and the first NADPH-diaphorase cells on 28PCD. These first cells are concentrated in the central part of the visual streak, and at subsequent ages, cells in this part of the streak have larger somata and more mature dendritic fields than those elsewhere, supporting the notion that the peak density region is a developmentally advanced part of the retina. Throughout development, amacrine cells of all classes are concentrated in the visual streak, with their density reaching minima at the superior and inferior retinal margins. As their total number increases, the difference in cell density between the streak and the periphery decreases, presumably because proportionately more cells are added at the periphery. Their total number peaks around 42PCD, followed by a decline of 12-31% to adult values. Once the peak number of cells has been reached, the difference in cell density between the streak and periphery begins to increase. The rate of this increase is closely correlated with the increase in retinal area. This redistribution of amacrine cells, as well as a greater expansion of their dendritic fields in peripheral retina, is almost certainly the product of nonuniform retinal expansion.