Transneuronal degeneration of beta retinal ganglion cells in the cat

Transneuronal retrograde degeneration of retinal ganglion cells was investigated following neonatal visual cortex ablation in the cat. After a survival time of at least 18 months, retinal ganglion cells projecting to the thalamus were labelled by retrograde transport of horseradish peroxidase. Filled ganglion cells were classified into alpha, beta and gamma types on the basis of dendritic morphology. In normal cats, alpha cells made up 8-10% of the total population in the sample area, beta cells made up 64-67% and gamma cells made up 23-27%. In retinae of visual cortex-ablated cats, normal numbers of alpha and gamma cells were present, but the beta cell population was depleted by 90% of normal. Thalamic projections of surviving retinal ganglion cells were investigated by anterograde transport of tritiated proline injected into the eye. In these animals, ablation of visual cortex resulted in almost complete degeneration of laminae A and A1 of the dorsal lateral geniculate nucleus. In the radioautographic material, projections from the retina to the degenerated parts of laminae A and A1 were barely detectable. Survival of some ganglion cell populations and death of others after neonatal visual cortex ablation may be explained in terms of the pattern of projections of the different cell types. We conclude that the majority of beta cells degenerate following visual cortex ablation because of removal of cells in the dorsal lateral geniculate nucleus which form their sole or principal target. Alpha and gamma cells and 10% of beta-cells survive because of extensive collateral projections to targets other than cells of the laminae A and A1 of dorsal lateral geniculate nucleus.