MORPHOLOGY OF M-CELL AXON ARBORS IN STRIATE CORTEX OF MONKEYS REARED WITH MONOCULAR APHAKIA

Although the effects of visual deprivation on the development of ocula r dominance columns have been well described in primates, nothing is k nown in primates about the impact of the deprivation on the axonal pro files that make up the ocular dominance columns. We now show that the effects of monocular deprivation on the morphology of geniculostriate axons involve not only shifts in terminal arbor sizes, much as would b e expected from the ocular dominance data, but also changes in the pro liferation of terminal arbor branches. In macaque monkeys reared from birth with unilateral lens removal (aphakia), terminal arbors of genic ulostriate axons were bulk-filled with horseradish peroxidase (HRP) in brain-slice preparations and reconstructed from serial sections throu gh striate cortex (area 17). Our focus was on the arbors that terminat e in the upper tier of layer TV, the target of cells in the magnocellu lar (M) layers of the LGN. Of the 26 M-cell arbors reconstructed from three aphakic monkeys, eight were unique in having few very simple ter minal arbor branches. These also tended to be smaller in total extent than the average M-cell axons reconstructed from 1 normal monkey. In c ontrast, eight arbors had very rich terminal branching patterns, and s even of these were larger than any of those from the normal monkey. We propose that the small, sparse axon arbors are related to the deprive d eye, and the large, dense arbors are related to the non-deprived eye . These morphological changes reflect abnormalities in the growth patt erns of geniculostriate inputs that undoubtedly have important persist ing consequences for visual performance. (C) 1998 Elsevier Science B.V . All rights reserved.