INFLUENCE OF PERIPHERAL-NERVE GRAFTS ON THE EXPRESSION OF GAP-43 IN REGENERATING RETINAL GANGLION-CELLS IN ADULT HAMSTERS

We have examined the ability of axotomized retinal ganglion cells in a dult hamsters, to regenerate axons into a peripheral nerve graft attac hed to the optic nerve and the expression of GAP-43 by these neurons. We also examined the effect on these events of transplanting a segment of peripheral nerve to the vitreous body. The left optic nerves in th ree groups of hamsters were replaced with a long segment of peripheral nerve attached to the proximal stump of the optic nerve similar to 2 mm from the optic disc to induce regeneration of retinal ganglion cell s into the peripheral nerve. An additional segment of peripheral nerve was transplanted into the vitreous of the left eye in the second grou p. The animals from the first and second groups were allowed to surviv e for 1-8 weeks and the number of regenerating retinal ganglion cells was determined by applying the retrograde tracer, Fluoro-Gold to the p eripheral nerve graft and the expression of GAP-43 was studied by immu nocytochemistry in the same retinas. As a control, a segment of optic nerve was transplanted into the vitreous body of the left eye in the t hird group of hamsters. These animals were allowed to survive for 4 we eks and the number of regenerating retinal ganglion cells was counted as in Groups 1 and 2. The percentages of the regenerating retinal gang lion cells which also expressed GAP-43 were very high at all time poin ts in Group 1 (with no intravitreal peripheral nerve) and Group 2 (wit h intravitreal peripheral nerve) and at 4 weeks for the Group 3 (with intravitreal optic nerve) animals. In addition, the number of regenera ting retinal ganglion cells, the number of retinal ganglion cells expr essing GAP-43 and the number of regenerating retinal ganglion cells wh ich also expressed GAP-43 were much higher in Group 2 than in Group 1 at all the time points and it was also much higher in Group 2 than in Group 3 at 4 weeks whereas there was no significant difference between the results from Groups 1 and 3 at 4 weeks. These data suggested that there was a close correlation between the number of the axotomized re tinal ganglion cells regenerating axons into the peripheral nerve graf t attached to the optic nerve and the expression of GAP-43. In additio n, the intravitreal. peripheral nerve, probably by releasing various n eurotrophic factors and by acting synergistically, can enhance the exp ression of GAP-43 in some of the axotomized retinal ganglion cells and promote the regeneration of retinal ganglion cells into the periphera l nerve graft.