| Research Abstract |
Retinal ganglion cells (RGCs) of mammals regenerate their axons into a grafted peripheral nerve segment, but numbers of regenerated RGCs are 2% in average. They are too small to intend functional recovery of impaired vision, or to guide axons of stem cell-derived RGCs into the central visual areas. Therefore, methods increasing the numbers should be developed. We tested several drugs which protect death of axotomized RGCs since survival of axotomized RGCs is the first requisite for axonal regeneration. We also obtained rate of axonal regeneration.
1. To develop a method promoting RGC survival, survival curve of axotomized RGCs were examined. Beta cells degenerate rapidly between day 3 to 7, while alpha cells did slowly until day 14. Death of beta cells in the rapid phase was due to apoptosis, and was able to be prevented with a caspase inhibitor. 2. We intravitrealy injected drugs which are reported to prevent rodent RGC death after axotomy. Combination of BDNF, CNTF and forskolin facilitated survival of cat RGCs, especially beta cells. Nipradilol (NP), an anti-glaucoma drug, protects injured RGCs from death at 10^<-7> mol.
3. Rates of prolongation of regenerated axons were estimated in cat RGCs. The average rate of whole RGCs was estimated as 1.1 mm/d. Alpha cells had the most rapid rate as 1.4 mm/d, compared with beta cells' (1.1 mm/d) and other cells' (1.0 mm/d). The highest rate of alpha cells reflects their greater ability to regenerate axons. The values are used as control values when a method to facilitate axonal elongation.
4. Combination of BDNF, CNTF and forskolin increased numbers of regenerated RGCs, but did not increase axonal regeneration of cells which survived axotomy without axonal regeneration. NP at 10^<-7> mol increased numbers of regenerated RGCs into 3-4 fold, and shortened time for 20 mm axonal elongation by 7 days.
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