Failure to restore vision after optic nerve regeneration in reptiles: interspecies variation in response to axotomy.
Optic nerve regeneration within the reptiles is variable. In a snake, Viper aspis, and the lizard Gallotia galloti, regeneration is slow, although some retinal ganglion cell (RGC) axons eventually reach the visual centers (Rio et al. [1989] Brain Res 479:151-156; Lang et al. [1998] Glia 23:61-74). By contrast, in a lizard, Ctenophorus ornatus, numerous RGC axons regenerate rapidly to the visual centers, but unless animals are stimulated visually, the regenerated projection lacks topography and animals remain blind via the experimental eye (Beazley et al. [2003] J. Neurotrauma 20:1263-1269). V. aspis, G. galloti, and C. ornatus belong respectively to the Serpentes, Lacertidae, and Agamidae within the Eureptilia, the major modern group of living reptiles comprising the Squamata (snakes, lizards, and geckos) and the Crocodyllia. Here we have extended the findings on Eureptilia to include two geckos (Gekkonidae), Cehyra variegata and Nephrurus stellatus. We also examined a turtle, Chelodina oblonga, the Testudines being the sole surviving representatives of the Parareptilia, the more ancient reptilian group. In all three species, visually elicited behavioral responses were absent throughout regeneration, a result supported electrophysiologically; axonal tracing revealed that only a small proportion of RGC axons crossed the lesion and none entered the contralateral optic tract. RGC axons failed to reach the chiasm in C. oblonga, and in G. variegata, and N. stellatus RGC axons entered the opposite optic nerve; a limited ipsilateral projection was seen in G. variegata. Our results support a heterogeneous response to axotomy within the reptiles, each of which is nevertheless dysfunctional.
Dunlop
Sarah A
SA
School of Animal Biology, The University of Western Australia, Crawley 6009, Australia. sarah@cyllene.uwa.edu.au
Tee
Lisa B G
LB
Stirling
R Victoria
RV
Taylor
Andrew L
AL
Runham
Phil B
PB
Barber
Andy B
AB
Kuchling
Gerald
G
Rodger
Jenny
J
Roberts
J Dale
JD
Harvey
Alan R
AR
Beazley
Lyn D
LD
D000818:Animals; D001369:Axons / Q000378:metabolism; D019771:Axotomy / Q000379:methods*; D001522:Behavior, Animal; D002232:Carbocyanines / Q000378:metabolism; D005247:Feeding Behavior / Q000502:physiology; D007839:Functional Laterality / Q000502:physiology; D007150:Immunohistochemistry / Q000379:methods; D066298:In Vitro Techniques; D009409:Nerve Crush / Q000379:methods; D009416:Nerve Regeneration / Q000502:physiology*; D009900:Optic Nerve / Q000378:metabolism / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D012104:Reptiles; D013045:Species Specificity; D013477:Superior Colliculi / Q000503:physiopathology / Q000528:radiation effects; D013997:Time Factors; D014785:Vision, Ocular / Q000502:physiology*; D014795:Visual Pathways / Q000503:physiopathology
C035005:3,3'-dihexadecylindocarbocyanine; D002232:Carbocyanines; D018809:Proliferating Cell Nuclear Antigen