Horizontal and amacrine cells in the mammal's retina

Abstract

The study of the retina of several mammals by both light and electron microscopy shows the existence of two types of horizontal cells: horizontal cells with a short axon, and horizontal cells without axon, which we can name “amacrine” cells of the outer plexiform layer. The horizontal cells with a short axon are related to cones. The amacrine cells of the outer plexiform layer make contacts with rods. Abundant membrane-to-membrane contacts, with total or partial fusion, can be seen between horizontal cells of both types as well as between them and the bipolar cells. In the retina of primates, only the horizontal cells with short axon have been seen. The horizontal cells of the monkey's retina show, in the soma, large processes and even in the thinnest terminals, the Kolmer “Kristaloide”. Such crystalline structures have been seen in the lateral processes of the cone “triads”. The membrane-to-membrane contacts between horizontal cells of the retina of primates adopt a structural aspect similar to that of the desmosomes. Both the diffuse and stratified type of amacrine cells have been found in all the retinae studies. A new cellular type, with processes expanding in both plexiform layers, have been seen in the cat's retina. A new cellular type, probably an amacrine cell, has been seen at the upper level of the ganglion cell layer. Horizontal and amacrine cells are not typical neurons. Due to their structure, disposition in plexus and electrophysiological response, they can be classified as a new type of nerve cell.