Functional Aspects of Optic Nerve Regeneration in Non‐Mammalian Vertebrates

Abstract

OverviewOptic nerve regeneration in fish and amphibia is largely successful with return of useful vision within one to two months, but is abortive in birds and mammals, with blindness persisting after nerve injury. Reptiles have an intermediate degree of success, with some species displaying robust regeneration and others only a limited degree. Nevertheless, in all reptiles tested behaviorally to date, animals are blind via the experimental eye. In the lizard Ctenophorus ornatus, although regeneration is robust, it is also highly inaccurate, with axons displaying a range of errors en route to visual targets. Crucially, a topographic map is not restored. Comparison of events in fish and lizard reveals that re-expression of guidance cues and recapitulation of an appropriate balance of excitatory glutamatergic and inhibitory GABAergic neurotransmission are crucial in restoring topography and therefore useful vision. Nevertheless, defects can be overcome by training lizards on a visual task with the result that topography is restored and animals are able to elicit visually elicited behavioral responses.

Regenerating optic axons restore topography after incomplete optic nerve injury

“…Many central projections are topographically organized and restoration of such ordered connectivity will be essential for functional repair (Kandel et al, 2000). The relative simplicity of the primary visual system has provided an excellent model to examine factors necessary for the restoration of topography after CNS injury (Meyer, 1998;Beazley, 2000a,b;Schmidt, 2004;Dunlop, 2006).…”