[Projection of different ganglion cell classes in the albino rat retina. A study using horseradish peroxidase].

In order to demonstrate the central projections of the different ganglion cell classes in the albino rat retina horseradish-peroxidase was injected into the superior colliculus (CS) and into the lateral geniculate nucleus (Cgl). The study presents the following results: a) Injection into the CS: Labelled cells are only in the contralateral retina. Topistically, the retino-collicular projection is in good agreement with the findings of physiological methods. The nasal half of the retina projects mainly to the posterior part and the superior half to the lataral part of the CS. Taking into consideration our cell-size-classification among 500 labelled cells we found 63% of the small group (7...10 micrometer soma diameter), 35% of the medium-sized (11...14 micrometer) and only 2% of the large group (15...23 micrometer). The small cells (W-system)project mainly, but not alone and not exclusively to the CS. b) Injection into the Cgl: In the ipsilateral retina we found a few labelled cells in the superior, temporal region. Contralateral--as after CS-injection--only half of ganglion cells is labelled. The quantitative analysis of 500 labelled cells indicates: 32% belong to hte small group, 51% to the medium-sized and 17% to the large group. There are fibers of all three classes, but in the majority those of the medium-sized class terminating in the Cgl. It is discussed whether these results allow a comparison of the size classes with the W-, X- and Y-system. Our findings show that there is no clear agreement between cell-size and projection site as demonstrated in cats. There is a large overlapping of the cell classes with respect to their central projection. We found that with increasing soma-diameter the ganglion cells project more and more to the Cgl. It is known that in the Golgi-picture cells with different soma diameter are of the same neuron type. Therefore, a morphological comparison of the ganglion cells of the rat with the W-, X- and Y-system is only ingenious taking into consideration also the dendritic structure.