THE COUPLING PATTERN OF AXON-BEARING HORIZONTAL CELLS IN THE MAMMALIAN RETINA

In most vertebrate retinae, horizontal cells of the same functional ty pe are homologously coupled through gap junctions. However, ultrastruc tural, 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 juncti on-permeant tracer, Neurobiotin, combined with photochromic intensific ation of the diaminobenzidine (DAB) reaction product, has revealed tha t the B-type horizontal cells in rabbit retina show strong tracer coup ling, both between the dendritic trees and between the axonal arboriza tions. These findings establish that the coupling pattern of axon-bear ing horizontal cells in a mammalian retina in qualitatively similar to the coupling patterns of axon-bearing horizontal cells in non-mammali an retinae.