Re-establishment of visual circuitry after optic nerve regeneration.

In mammals there are a few circumstances in which axotomised ganglion cell axons can regenerate. For instance, in vitro explants of retina can be encouraged to regenerate axons into appropriate culture media. Similarly, axotomised ganglion cells can regenerate into a peripheral nerve graft surgically connected to the optic nerve head, and during early development axons are able to regenerate across the retina to re-enter the optic nerve. This is certainly encouraging, but we are a long way from applying these observations to clinical practice. We need to know whether regenerating axons also retain a functional capacity for navigation. We must ask whether a regenerated projection is likely to be topographic rather than disordered. In this brief review we will look at some selected models of ganglion cell regeneration in order to examine this question of navigation in more detail. This is an important issue: the capacity to re-establish appropriate rather than random connections after ganglion cell regeneration would most likely be necessary for any meaningful return of visual function.