The course of regenerating retinal axons in the frog chiasma: the influence of axons from the other eye.

There is evidence, from a variety of species, that axons arising from the two eyes interact as they pass through the optic chiasma. In this paper we examine the effect of altering the composition of the normal chiasmatic environment on the course taken by regenerating axons in Xenopus. We show that the usual contralateral route of such axons in the optic chiasma is not affected by the absence of axons from the other eye. We have not observed any influence of embryonic enucleation, or eye removal before the onset of metamorphosis, on either the normal ipsilaterally projecting axons or the contralateral route taken by regenerating axons. Further, we have found no effect of the degeneration of the other projection, either for long or short periods of time, suggesting that axonal debris does not influence the course of regenerating axons. The simultaneous regeneration of the two projections also has no effect on the trajectory of regenerating axons. We conclude that in spite of the close association of axons from the two eyes in the chiasma, there is no interaction involved in Xenopus in the generation of the decussation pattern.