Regeneration of retinotectal projections after optic tectum removal in adult newts.

Purpose: When injured, the adult newt possesses the remarkable capability to regenerate tissues and organs with return of function and physiology. One example is the newt eye, in which regeneration can restore normal vision if the retina or lens has been removed. We wanted to examine how the retinotectal projections regenerate after removal of the brain's optic tectum and establish this animal as a model for retinal projection as well as a central nervous system regeneration model.

Methods: A major portion of the left optic tectum was removed in several adult newts, and the animals were monitored postoperatively for eight months to observe regeneration and innervation. Cell proliferation was examined by histological methods and by BrdU incorporation.

Results: We observed that adult newts have the capability to the excised optic tectum. As indicated by horseradish peroxidase staining, 80% of the retinotectal projection area was regenerated eight months after the operation, even though the wound closed much earlier. Our study provides the first quantitation of regeneration of the retinotectal projections. The ependymal cells that line the ventricle were the most likely source of the regenerated tectum. After removal, cell proliferation was detected only in the ependymal cells layer. Double staining of proliferating cells and neurons was limited, indicating that direct transition of ependymal cells is a possibility.

Conclusions: The retinotectal projections after removal of the adult newt optic tectum can be readily re-established. Thus, this model can become indispensable for the study of vision restoration and neurogenesis.