γ -aminobutyric Acid Antagonists Decrease Junctional Communication between L-Horizontal Cells of the Retina

The antagonists of γ -aminobutyric acid, bicuculline and picrotoxin, were found to narrow the receptive field profile of the large field horizontal cell (L1HC) in the turtle retina when added to the perfusion medium in micromolar concentrations. The coupling resistance between neighboring L1HCs was increased by bicuculline or picrotoxin. Under control conditions, the dye Lucifer yellow injected into one L1HC diffused into a large number of neighboring L1HCs; bicuculline or picrotoxin greatly restricted dye passage between these same cells. We conclude that antagonists of γ -aminobutyric acid decrease the conductance of gap junctions between L1HCs.