EARLY FUNCTIONAL NEURAL NETWORKS IN THE DEVELOPING RETINA

IN the adult mammalian retina, the principal direction of information flow is along a vertical pathway from photoreceptors to retinal intern eurons to ganglion cells, the output neurons of the retina. We report here, however, that initially in development, at a time when the photo receptors are not yet even present, there are already functionally def ined networks within the retina. These networks are spontaneously acti ve rather than visually driven, and they involve horizontal rather tha n vertical pathways. By means of optical recording using the calcium-s ensitive dye Fura-2, we have found that sets of retinal ganglion cells and amacrine cells, a type of retinal interneuron, undergo synchroniz ed oscillations in intracellular calcium concentration, These oscillat ions are highly correlated among subgroups of neighbouring cells, and spread in a wave-like fashion tangentially across the retina, Thus, in development of retinal circuitry, the initial patterning of neuronal function occurs in the horizontal domain before the adult pattern of v ertical information transfer emerges.