Plasticity in innervation of the rat superior colliculus by transplanted retinae as a result of eye removal at maturity.

When the superior colliculus of a rat is innervated by inputs from both eyes as well as a retina transplanted intracranially over one tectum at birth, the tectal projection from the transplant is confined mainly to the superficial surface of the superior colliculus. The transplant-derived fibers possess a simple morphology, lacking terminal arborizations. If the contralateral eye is removed one month after transplantation, these fibers can be induced to arborize into the denervated portion of the superior colliculus over the next month. This demonstration of sprouting in a mature sensory relay system raises the possibility that an enhancement of behavioral responses mediated by transplanted retina might also occur. In turn, this may provide an ideal system to study the correlation between anatomical changes in transplant axons and changes in behaviors mediated by transplant activity.