Role of retinal afferents in regulating growth and shape of the lateral geniculate nucleus.

Segregated binocular maps in the dorsal lateral geniculate nucleus (LGN) develop from a stage where they initially overlap. Sophisticated computational models have been used to describe the dynamics of three-dimensional LGN shape changes that play a role in segregation. These models have revealed specific nuclear growth vectors associated with the process of ocular segregation in the LGN (Williams and Jeffery [2001] J Comp Neurol 430:332-342.). In this study, we use similar techniques to determine whether retinal innervation contributes to the dynamics of shape maturation in the ferret LGN. In this animal, 90% of the retinal innervation of the mature LGN comes from the contralateral eye. If one eye is removed before segregation, the projection from the remaining eye remains diffuse and nuclear growth is stunted. Here, we quantify this effect and show that removing the contralateral projection before segregation has a profound impact on LGN size but changes its ultimate shape by only 12%. The impact on shape on the other side of the brain where the ipsilateral projection is removed, which accounts for only 10% of its innervation in maturity, is less than 2%. Hence, retinal innervation plays a minor role in determining mature LGN shape. Although in both hemispheres, the ultimate shape of the nucleus is close to normal, removal of the larger projection disrupts normal growth vectors, with almost none being present in the 5 days after enucleation, when the normal nucleus expands markedly. Hence, the effect of enucleation is to delay shape maturation. Growth vectors absent after removal of the smaller projection are mainly confined to those in what would be the binocular region. Copyright 2002 Wiley-Liss, Inc.