Organization of geniculocortical connections following prenatal interruption of binocular interactions.

The organization of geniculostriate connections in normal cats was compared with that of adult animals that were uniocularly enucleated before birth. In normal animals microelectrophoretic deposits of horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) into the A-lamina of the dorsal lateral geniculate body (LGd) resulted in anterograde label in layers IV and VI and labeled cells in layer VI of areas 17 and 18. The labeling pattern within both of these cortical areas consisted of alternating patches separated by zones of equivalent size that were relatively free of label. In the normal animals no reaction product was evident in any other cortical area. In the prenatally enucleated cats, the LGd both contralateral and ipsilateral to the remaining eye is comprised of only two distinct cell layers. The dorsal layer appears to be a composite of the normal A/A1-laminae, while the ventral layer appears to correspond to the C-laminae. Deposits of WGA-HRP into the superficial aspect of the A/A1 layer yielded a dense continuous band of label within layers IV and VI of areas 17 and 18. Additionally, such deposits in the prenatally enucleated cats also revealed an anomalous reciprocal connection with area 19. Punctate deposits of WGA-HRP into cortical area 19 of the fetal enucleates resulted in the labeling of two distinct populations of cells within the A/A1 layer of the LGd. No cells were labeled within the A-laminae following such deposits into area 19 of normal animals. The geniculocortical connections of the prenatally enucleated cats, including that to area 19, were found to be retinotopically organized. These results indicate that in utero interruption of binocular interactions prevents the formation of ocular dominance domains within areas 17 and 18 of the cat's visual cortex. This could reflect the maintenance of exuberant geniculocortical projections present at the time of prenatal eye removal as originally suggested by Rakic (Science, 214 (1981) 928-931). The anomalous connection with area 19, on the other hand, could be due to the disruption of LGd cell migration resulting from the early eye removal.