Electrical coupling between horizontal cell bodies in the tiger salamander retina

We studied lateral interactions between horizontal cells in the tiger salamander retina in order to determine the underlying mode of synaptic transmission. Pairs of cells, visually identified by inspection of the in vitro retinal slices, were impaled with two separate electrodes and the transmission between them was examined by injecting current into one cell while recording the resulting voltage response from the other soma. It was found that coupling between horizontal cells remained intact and even increased somewhat during the light response and in the presence of cobalt or acetylcholine. It was also observed that a fluorescent dye injected into one cell would often migrate and stain neighbouring horizontal cells. These results suggest that synaptic transmission between horizontal cell bodies is mediated mainly by electrotonic conduction. The increase in apparent coupling observed under certain experimental conditions can be explained by the increase in input resistance of each horizontal cell.