Yun, Bai Zeng; (1993) An experimental anatomical study of degenerative and regenerative responses following injury to the optic nerve in adult rats. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis is focused on the responses of the retinal ganglion cell (RGC) in adult rats to optic nerve injury, and in particular on the formation, elongation and regression of axonal sprouts under different conditions. In four series of animals, the ultrastructural and temporal characteristics of the sprouting response were examined (by LM and EM) in the proximal stump of the optic nerve following either intraorbital (proximal) or intracranial (distal) optic nerve transection, after both relatively short survival times (1–7 days) and after longer periods (1 to 8 weeks). In some animals, RGC axonal sprouts were labelled by anterograde tracers (DiI and RITC for LM and confocal microscopy; horseradish peroxidase for EM). After proximal lesion, sprouting is extensive at 2–7 dpo but few sprouts survive beyond 2–3 weeks. After distal lesion, sprouting is less extensive but sprouts persist for longer. In further series of animals, the presence of the growth associated protein GAP - 43 in RGC and optic axons was studied qualitatively and quantitatively by immunofluorescence in retinal wholemounts (and by EM immunocytochemistry) after either intraorbital or intracranial optic nerve section. GAP - 43 positive RGC appeared 5 days–8 weeks (peak at 4 weeks) after both proximal and distal lesion but were ca. 10 times more numerous after proximal lesion. In another series of animals, a sprout—sustaining effect of the acellular components of a peripheral nerve graft was found by suturing a segment of peroneal nerve in which all cells had been destroyed by repeated freezing and thawing to the proximal stump of intraorbitally transected optic nerves. In a final series of experiments, the possibility that humoral factors from injured peripheral nerves affect RGC survival and axonal regeneration after axotomy was demonstrated by suturing the proximal (retinal) stump of intraorbitally transected optic nerve into the proximal end of a silastic tube and a segment of peroneal nerve into the distal end of the tube, with the two stumps initially separated by a gap of about 5mm. The findings in these experiments are discussed in the light of current hypotheses about the failure of regeneration in the adult mammalian CNS.

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