Transneuronal effects of early eye removal on geniculo-cortical projection cells.

Iontophoretic injections of horseradish peroxidase (HRP) were made into the primary visual cortex of normal rats, and into the visual cortex ipsilateral to the remaining eye of neonatally enucleated rats. The distribution of retrogradely labelled cells in the dorsal lateral geniculate nucleus (LGNd) in the two groups was compared. In normal animals labelled cells were found running in a discrete column through LGNd following the relevant line of projection. In enucleated animals the cells were less tightly grouped through the structure, although the lines of projection coursed in the same general direction. These results suggest that the consequences of early monocular enucleation upon the retinal projection from the remaining eye are transmitted beyond the regions receiving direct input from the eye to secondary visual projections.