Axon arbors of X and Y retinal ganglion cells are differentially affected by prenatal disruption of binocular inputs.

In the mammalian visual system, the terminal arbors of retinal ganglion cell axons from the two eyes are restricted to mutually exclusive territories within their thalamic target, the lateral geniculate nucleus (LGN). Here we have investigated some of the factors that determine the adult morphology of terminal arbors in the cat's retinogeniculate system. Removal of one eye during prenatal life at a time when retinogeniculate axons from the two eyes are extensively intermixed within the LGN perturbs the subsequent morphological development of some but not all axons from the remaining eye. The presence of terminal arbors qualitatively normal in size, shape, and location within the LGN suggests that for some retinal axons, ongoing binocular interactions throughout prenatal life are not needed for the development of normal arbor morphology. However, many of the axons form arbors of abnormal size or location, suggesting that such features of axon morphology are not intrinsically determined for these axons but may be susceptible to external influences. Electrophysiological studies reveal that the abnormal arbors all belong to the functionally distinct Y class of retinal ganglion cells, whereas the normal arbors all belong to X cells. The different responses of X and Y axons to prenatal enucleation demonstrate that during development subsets of a single neuronal population projecting to the same target in the central nervous system can be under different developmental controls for axon arbor differentiation.