Timing of fiber arrival and dennervation of postsynaptic neurons is required for restoration of visual perception by regenerating axons.
Axotomized CNS neurons, whose regenerating axons are guided to their natural target areas in the brain with the aid of peripheral nerve grafts, are capable of establishing synaptic contacts with normal morphological and electrophysiological properties. The present study was undertaken to analyse the functional significance of the reestablished synaptic contacts made by these regenerated retinofugal neurons. Adult rats were trained in a T-maze to obtain a food reward with the aid of visual cues. One of their optic nerves was transected and the regenerating axons were guided into the optic tract with a peripheral nerve graft, in order to enable them to reinnervate the superior colliculus (SC) and thalamus. Postoperative testing of the animals showed a drastic improvement of visual perception. The protocol of dennervation of the SC (prior to, simultaneous or with a delay with respect to fiber arrival) determined the performance of the animals. Rats belonging to the first two groups performed almost as well as they did prior to the transplantation. The functional integrity of the retina was assessed by electroretinography (ERG) which revealed typical rod spectral sensitivity at 380 and 500 nm, but reduced responsiveness to illumination. In accordance, neuroanatomical assessment of the retinal ganglion cells revealed that about 15% of the axotomized neurons contributed to regeneration of axons. These findings show that a restricted population of retinofugal axons of capable of restoring higher visual functions such as light-discrimination-behaviour in the adult rat. Prerequisites for the restoration of visual perception are first the preservation of the intraretinal integrity, and second the temporal matching of fiber arrival and dennervation of postsynaptic neurons.
Thanos
S
S
Department of Ophthalmology, University of Tübingen, School of Medicine, Germany.
Naskar
R
R
Mey
J
J
Schaeffel
F
F
D000818:Animals; D001369:Axons / Q000648:ultrastructure*; D004596:Electroretinography; D008636:Mesencephalon / Q000648:ultrastructure; D009474:Neurons / Q000648:ultrastructure*; D017729:Presynaptic Terminals / Q000502:physiology*; D051381:Rats; D012038:Regeneration / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*