An anatomical investigation of projections from lateral geniculate nucleus to visual cortical areas 17 and 18 in newborn kitten.

The presence of projections from the lateral geniculate nucleus to visual cortical areas 17 and 18 in newborn kitten was examined using the method of retrograde axonal transport. An injection of either horseradish peroxidase (HRP) or horseradish peroxidase conjugated to wheat germ agglutinin (HRP-WGA) was made into area 17 on one side of the brain and area 18 on the other side. The results were not unlike those from experiments on adults. Area 17 injections label a relatively high proportion of cells in laminae A and A1 and the distribution of sizes of labelled cells is almost the same as that for the total cell population. Area 18 injections label only a small percentage of the total cell population in laminae A and A1 and most of the labelled cells are large. Cells in the C layers are labelled after an injection into either area 17 or 18. It was concluded that the formation of organized thalamocortical projections in the kitten does not rely on visual experience as the projections are already present at birth.