Two types of orientation-sensitive responses of amacrine cells in the mammalian retina.

Neurons sensitive to the orientation of light stimuli exist throughout the mammalian visual system, suggesting that this spatial feature is a fundamental cue used by the brain to decipher visual information. The most peripheral neurons known to show orientation sensitivity are the retinal ganglion cells. Considerable morphological and pharmacological data suggest that the orientation sensitivity of ganglion cells is formed, at least partly, by the amacrine cells, which are laterally oriented interneurons presynaptic to the ganglion cells in the inner plexiform layer. So far there have been few studies of the responses of amacrine cells to oriented visual stimuli and their role in forming orientation-sensitive responses in the retina remains unclear. Here I report the novel finding of a population of amacrine cells in the rabbit retina which are orientation-sensitive. These amacrine cells can be divided into two subtypes, whose orientation sensitivity is manufactured by two distinct mechanisms. The orientation sensitivity of the first subtype of amacrine cell is formed from the interactions of excitatory, centre-receptive field synaptic inputs and inhibitory inputs of opposite polarity, whereas that for cells of the second subtype seems to be the product of a marked asymmetry in their dendritic arbors.