Reduced conduction velocity of retinal Y-cell axons following early partial removal of their synaptic targets.

Following unilateral visual cortex ablation in neonatal kittens, the extraretinal conduction velocities of retinal Y-cell axons projecting to the lesioned hemisphere were measured and compared to the velocities of Y-cell axons projecting to the intact hemisphere. The extraretinal velocities of Y-cells projecting to the lesioned hemisphere were 16-28% lower than the velocities of Y-cells projecting to the intact hemisphere. This effect was seen in axons originating in both the ipsilateral and contralateral retinae. These data are consistent with the hypothesis that one factor regulating axon size is the amount of synaptic territory which is available to the cell. When the velocities of the unmyelinated intraretinal portions of Y-axons were examined in experimental animals, no significant differences could be detected between axons projecting to the lesioned hemisphere and those projecting to the intact hemisphere.