Regeneration of functional synaptic connections between widely separated neurons in the adult mammalian central nervous system.

The responses to light of retinal ganglion cells with regenerated axons can be recorded from axons teased from peripheral nerve grafts replacing the optic nerve of the adult rat or hamster. These responses resemble those of normal retinal ganglion cells but can no longer be observed several months after grafting, concomitant with ongoing loss of the population of axotomized retinal ganglion cells. Synapses formed with neurons in the superior colliculus by retinal ganglion cell axons regenerated through peripheral nerve grafts mediate both excitatory and inhibitory responses. These experiments demonstrate that when provided with an appropriate milieu for elongation, neurons indigenous to the adult mammalian central nervous system can make functional reconnections with distant targets within the nervous system.