Axons of alpha ganglion cells regenerate faster than other types into a peripheral nerve graft in adult cats.

We reported previously that alpha ganglion cells in the cat retina have the highest ability in axonal regeneration. To examine whether alpha cells regenerate axons faster, we estimated the rate of axonal regeneration of retinal ganglion cells (RGCs) with transplantation of a peripheral nerve (PN) segment. After 4, 6, and 8 weeks of survival, regenerated RGCs were double-labeled with two fluorescent dyes injected separately at 10 mm and 20 mm from the connected site. From a scatter diagram of double-labeling ratios, we estimated that axons reached 20 mm by 3.2 weeks. Immunostaining suggested that first axon sprouts entered a PN segment on Day 4. These values enabled us to estimate average rates of axonal regeneration as 1.1 mm/day for all the RGCs. Proportions of cell types of regenerated RGCs were obtained with Lucifer yellow injections, and those of alpha cells were higher than those in normal retinas in any periods. From analysis of scatter diagrams, we estimated axonal growth rate of alpha, beta, and non-alpha/beta cells as 1.4, 1.1, 1.0 mm/day, respectively. The higher regeneration rate of alpha cells may reflect greater regenerative ability compared to other cell types. The present system also provides control values when a method to promote axonal regeneration is developed.