The Coupling Pattern of Axon-Bearing Horizontal Cells in the Mammalian Retina

In most vertebrate retinae, horizontal cells of the same functional type are homologously coupled through gap junctions. However, ultrastructural, physiological and dye-coupling studies have shown that the axon terminals of horizontal cells in mammalian retinae are not connected by gap junctions. In this study, intracellular injection of the junction-permeant tracer, Neurobiotin, combined with photochromic intensification of the diaminobenzidine (DAB) reaction product, has revealed that the B-type horizontal cells in rabbit retina show strong tracer coupling, both between the dendritic trees and between the axonal arborizations. These findings establish that the coupling pattern of axon-bearing horizontal cells in a mammalian retina in qualitatively similar to the coupling patterns of axon-bearing horizontal cells in non-mammalian retinae.