Electrical feedback mechanism in the processing of signals in the outer plexiform layer of the retina.

In any chemical synapse there is an electrical feedback initiated by the electrical current generated by the postsynaptic neurone. We argue that this feedback can be rather effective in the case of invaginating synapses in the retina. A model of a dyad synapse (cone-horizontal cell-bipolar cell) is developed, in which the transfer function between the cone and bipolar cell is modulated by the synaptic current of the horizontal cell. This modulation originates by the change of the potential drop along the intercellular gap between the cone and the horizontal cell. The model takes into account the electrical coupling between the horizontal cells as well as the nonlinearity of their nonsynaptic (somatic) membrane. The model reproduces qualitatively the steady-state responses of an hyperpolarizing bipolar cell to the light spot and an annulus. It gives also the adaptational (with a light background) shift of the cone-bipolar cell transfer function. The model can be applied to depolarizing bipolar cells and to C-type horizontal cells.