How do cone inputs reach the axon terminal?
The horizontal cell axon does not transmit signals from axon terminal to soma, but so far the possibility of signal transmission in the opposite direction has not been examined in the mammalian retina. To test whether cone signals reach the axon terminal via rod–cone coupling or by way of the horizontal cell soma and axon, we recorded light responses of horizontal cell axon terminals from Cx36-deficient retinas. We reasoned that if, in the wild type, cone signals reach the axon terminal by way of rod–cone gap junctions, then light responses of axon terminals from Cx36-deficient retinas should resemble those obtained from CNGA3-deficient retinas, in which the cone component of the light responses was missing. Light responses of an axon terminal from a Cx36-deficient mouse are shown in Figure 6B. These light responses closely resemble those obtained from somata from this mouse line, and are also very similar to axon terminal responses obtained from rhodopsin-deficient retinas (Fig. 4C),
