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

Abstract

EFFERENT retinal fibres originating in the nucleus isthmo-opticus^1,2 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 cells^6,7. 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.