SOME HORIZONTAL CELLS OF THE BOVINE RETINA RECEIVE INPUT SYNAPSES IN THE INNER PLEXIFORM LAYER

Bovine retinae were stained immunocytochemically with antibodies again st the calcium-binding protein, calbindin. Horizontal cells in the out er plexiform layer were heavily labelled. The processes of most horizo ntal cells were confined to the level of the outer plexiform layer, an d the tips of their dendrites were positioned as the lateral elements of the cone triads, viz. the usual mammalian arrangement. However, som e of the horizontal cells had additional thick processes descending to branch within the inner plexiform layer, where they were postsynaptic at bipolar cell dyads and where they also received input from amacrin e cells. No output synapses of horizontal cells were observed in the i nner plexiform layer.