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Abstract:
The ganglion cell dendrites of the rat retina were investigated by means of the strongly fluorescent, non-polar carbocyanine dye 1,1-dioctadecyl-3,3,3',3'-tetramethyl-indocarbodyanine perchlorate (diI or diI-C18-3 or D282) which was taken up by retinofugal axons and transported in the retrograde direction. The dye completely outlined the somata, the axons and the dendritic trees of several retinal ganglion cells and allowed qualitative and quantitative investigations. By means of this labeling technique, the diameters were determined in 272 dendrites and somata of various ganglion cell sizes. A comparison of the measurements with those reported in the literature revealed that the diI could be taken up by all classes of retinal ganglion cells. The most frequently labeled cells were those of class II, which have small to middle-sized perikarya (16.7 +/- 2.5 microns in diameter) and small to middle-sized dendritic trees (187 +/- 70 microns in diameter) with a high branching frequency (88 +/- 19 branching points). Retinal ganglion cells of class I were less frequent and have large perikarya (21.9 +/- 3.4 microns in diameter) with large dendritic trees (318 +/- 55 microns in diameter) and medium branching frequency (60 +/- 19 branching points). Class III cells which were described incompletely in the literature, appeared to be small to middle-sized in their perikaryal diameter (15.9 +/- 2.5 microns) but have large dendritic trees (299 +/- 63 microns in diameter) and a low branching frequency (40 +/- 10 branching points). In about 10% of the retinal ganglion cells with completely filled dendritic fields, the somata were situated outside the dendritic extensions, as viewed on the whole mounted retina. These "asymmetric" retinal ganglion cells appeared to belong to class II cells and were evenly distributed throughout the entire retina and were not related to neighboring blood vessels. The orientation of the asymmetric dendrites was random in relation to the optic disc. The axons of asymmetric retinal ganglion cells were almost always oriented opposite to the direction of the dendritic trees. If the dendrites extended towards the optic disc, the proximal parts of the corresponding axons were oriented towards the periphery of the retina, turning then at 180 degrees to the optic disc. Less than 1.5% of the retrogradely filled cells were displaced ganglion cells and extended dendritic trees within the deep inner plexiform larger.
