Retinal transplants in congenitally blind mice: patterns of projection and synaptic connectivity.

Embryonic retinae were transplanted onto the midbrain of neonatal congenitally anophthalmic mice and neonatal mice from which both eyes had been removed. When donor mice of the AKR strain were used, the detailed patterns of the transplant projections to the host brain were demonstrated with an antibody to Thy-1.1, which specifically stains neural tissue derived from AKR donors. Many of the subcortical visual centers were innervated, and only small differences were encountered between anophthalmic and eye-enucleated mice. The terminal arbors of transplant-derived axons could not be classified as in normal animals, although several distinct arbor types were seen. In the superior colliculus, the laminar arrangements that characterize normal retinal arbors were disrupted. Despite this, the synaptic patterns formed by transplant-derived axons in the superior colliculus of anophthalmic mice compared very closely with those of retinal axons in normal, sighted animals. These observations indicate that the ability of a retinal transplant to innervate the host brain and to form the synaptic arrays characteristic of optic terminals are not dependent on prior innervation, nor do they appear to be influenced by the events that follow eye removal.