Developmental regulation of the morphology of mouse retinal horizontal cells by visual experience.

Visual deprivation during development alters the normal refinement of connections, neurotransmitter expression and physiological function in the retina. We investigated the effects of different forms of visual experience on the anatomy of retinal neurons in the mouse. Although it is generally assumed that outer retinal cells are not affected morphologically by visual experience, we found changes in the outer retinas of animals reared with light but no contrast. In postnatal day 30 animals reared in control, dark and high-contrast environments, horizontal-cell processes ramified normally in the outer plexiform layer. However, in postnatal day 30 no-contrast-reared retinas, horizontal-cell processes emerged from the outer plexiform layer and ramified in the inner nuclear layer. Similar sprouting processes of horizontal cells were found in a mouse model of retinitis pigmentosa. In conclusion, our data show that a lack of contrast during development alters the morphology of horizontal cells and may thus affect normal visual processing. This effect may be relevant for young patients with cloudy vision (e.g. cataract).