A new method to selectively injure the optic nerve using argon-laser photocoagulation.

To create a model by noninvasive means for the study of Wallerian and transneuronal degeneration of the central nervous system, we devised a two-step argon laser photocoagulation (ALP) procedure with which we could selectively injure the optic nerve in rats. Changes in the optic nerve distal to the site of injury were studied histologically to evaluate this method; we succeeded in selectively and completely injuring the optic nerve. We found this ALP technique to be superior to either the panretinal or one-step photocoagulation method. Changes within astrocytes of the intracerebral optic tract and the lateral geniculate body in animals were also studied immunohistochemically following ALP and compared with those which follow enucleation. Reactive astrocytes with enhanced immunoreactivity for glial fibrillary acidic protein (GFAP) increased in number in the intracerebral optic tract and in the lateral geniculate body on the contralateral side of the optic injury in both groups of animals. The increased GFAP immunoreactivity was sustained for 6 weeks following injury; the proliferative tendency of the glial cells, shown by the bromodeoxyuridine method, peaked 3 days after injury and then decreased gradually. These glial responses in the optic tract and lateral geniculate body of animals subjected to ALP are similar to those of animals following enucleation. Our results indicate that this new technique for selectively and noninvasively injuring the optic nerve with ALP is applicable to the study of Wallerian and transneuronal degeneration.