Experiments to determine whether retinogeniculate axons can form translaminar collateral sprouts in the dorsal lateral geniculate nucleus of the cat

An earlier study has shown that in young kittens, but not in adult cats, section of one optic nerve produces a curious pattern of cell survival in the denervated geniculate laminae. Most of the cells in these laminae are shrunken, but a few large cells remain close to the borders of the adjacent, normally innervated laminae, giving the impression that these cells are sustained by collaterals arising from the normal retinogeniculate axons. Adult cats and kittens aged 7, 9 and 20 days have been used to determine the extent to which normal retinogeniculate axons can invade a denervated geniculate lamina. One eye was removed and the animals were kept for periods varying from four months to four years. The fiber degeneration produced by removal of the second eye was then studied. There is no evidence for any collateral sprouting in the adults. If the first operation is done at seven or nine days a limited number of axons grow across laminar borders and invade a small border zone of the denervated laminae. These axons do not appear in all of the regions that show surviving large border cells. It is concluded that new sprouts are probably not formed, but that growing axons can invade an inappropriate lamina if this is denervated during the normal period of axonal growth.