A new type of wide-field horizontal cell, presumably linked to blue cones, in rabbit retina

Abstract

Horizontal cells of vertebrate retina play an important role in the formation of visual receptive field surrounds of bipolar cells 21,39, and hence in the centre-surround receptive field organization of retinal ganglion cells. In some retinas, horizontal cells also play a major functional role in the first stage of colour-coding of visual stimuli 16,34. We have identified a new type of horizontal cell, called ‘type C’, in rabbit retina, which unlike type A and type B horizontal cells, contacts only a small fraction of cone photoreceptors, possibly blue cones. The multiple, sparsely branched axons of type C cells are well-positioned to contact bipolar dendrites in a feedforward manner. In summary, we propose (1) that the presence in rabbit retina of 3 types of cone horizontal cell, A, B, and C, may represent a more common pattern in mammalian retinae, shared with many non-mammalian retinas which contain colour-coded neurons, (2) that type C cells connect principally to blue cones, and (3) that type C cells are more common in retinas, such as those of squirrels, and to a lesser extent rabbits, in which blue cones play a major role in the colour coding of visual signals.