Influence of efferent retinal fibres on responsiveness of ganglion cells to light.

Abstract

EFFERENT retinal fibres originating in the nucleus isthmo-opticus1,2 of the pigeon have been shown, by electron microscopy, to terminate directly on amacrine cells3. These findings support the notion of a centrifugal control, originating at the brain, on the retina. Centrifugal fibres exist in several other non-mammalian species4, but their precise site of termination in the retina has not been determined. In the turtle, stimulation of centrifugal fibres at the level of the optic nerve has a powerful excitatory effect on amacrine cells since it produces a large, “all-or-none” excitatory postsynaptic potential (e.p.s.p.)5. Such excitation is in turn transmitted to ganglion cells5 through the extensive connections between amacrine and ganglion cells6,7. Thus ganglion cells are influenced both by the visual input through photoreceptors and other retinal cells, and by a centrifugal input possibly mediated by amacrine cells alone. We describe here some preliminary results concerning the interactions between these two inputs to the ganglion cells.