Horizontal Cell Layer Research Articles

ATPase activity at the functional contacts between retinal cells which produced S-potential.

ACCORDING to Cajal1, the horizontal cells of the teleost retina are arranged in three superimposed tangential layers formed by the external, medial and internal horizontal cells. Cajal classified the horizontal cells as short axon (Golgi II) cells and showed that radially oriented apical processes make contact with the receptor endings. Golgi studies and ultrastructural studies on the teleost retina (refs. 2 and 3 and unpublished results of V. Parthe and myself) confirm Cajal's description of these cells which in certain teleosts are enormous compared with the bipolar cells in the same retinal layer. Thin tangentially oriented extensions were not found in the external horizontal cells in Parthe's Golgi material. Such extensions of the medial and internal horizontal cells do not exceed in length the diameter of the cell body. Axon-like structures were not seen by Parthe or myself in any of the horizontal cell layers. In ultra-structural work4 each row of horizontal cells appears as a reticulum in which the cells are interconnected by membrane to membrane apposition of their lateral processes. Yamada and Ishikawa3 described in the carp, shark and ray retinae “fused membrane structures” at the apposition areas between the short lateral processes of the horizontal cells. But specialized junctions were not seen between horizontal cells belonging to different layers. These findings have been confirmed (Fig. 1) and similar fused membrane structures have been seen between stellate amacrine cells and between interstitial amacrine cells, in the regions where membrane to membrane contacts are formed between adjacent cells (my unpublished work). Light and electron microscopy shows that all the cells, which are of a giant size in certain teleost retinae, form tangential networks which are continuous throughout the retina (ref. 5 and unpublished results of V. Parthe and myself). Synaptic vesicles have not been observed in the region of the fused membrane structures (Fig. 1).

Ganglion, amacrine and horizontal cells of the cat's retina

Cell types in the cat's retina were stained by methylene blue given intravitally and by a modification of the Gros-Bielschowsky silver impregnation technique. The dendritic arborisations of the cells were studied in whole mounts and in sections. In peripheral retina each ganglion cell had a horizontal dentritic spread confined to one zone of the inner plexiform layer, usually within its outer half. The diameter of this dendritic arborisation ranged from 18–710μ and all intermediate sizes were seen. In general the cells with large dendritic fields had 3–5 main dendrites arising from the cell body and passing obliquely through the inner plexiform layer to branch in the zone of horizontal spread. The cells with small fields had a single main dendrite passing vertically through the inner plexiform layer. Some small fields had a loose dendritic network, and others a dense ramification of fine dendrites. In the central area of retina ganglion cells were found with a dendritic spread of less than 15μ. Amacrine cells were seen in the outer half of the inner plexiform layer. At the outer edge of the bipolar cell layer, a layer of horizontal cells was well seen in the silver stained retinas.