Abstract
Purpose: :
It has been reported that OFF–center retinal ganglion cells (RGCs) in cats have smaller ability to regenerate their axons into a transplanted peripheral nerve (PN) than ON–center RGCs. We examined whether regeneration of OFF–center RGCs is promoted when number of the RGCs is increased.
Methods: :
Transection of optic nerve (OpN): Most of RGCs were labeled with DiI. The left OpN of anesthetized cats was completely cut. The both retinas were dissected at day 14. Transplantation of PN: A PN was transplanted to the cut left OpN. At week 6, regenerated RGCs were labeled with dextran–Texas Red. After 2–3 days, the transplanted retina was dissected. Analysis of dendritic ramification in IPL: After regenerated RGCs were injected with LY, the retinas were fixed with paraformaldehyde. To visualize the outer border of IPL, processes of dopamine amacrine cells were immunostained with anti–tyrosine hydroxylase antibody. Dendritic depth of LY–injected RGCs was measured using NeuroLucida in flat–mounted retinas, and determined to ramify in sublamina a (OFF) or b (ON).
Results: :
With our analysis, ON– and OFF–ratio was 1.26 (ON 56%, OFF 44%) in the normal cat retina, slightly number of ON–RGCs was greater. In regenerated RGCs with saline injection (control), the ratio increased to 2.61 (ON 72%: OFF 28%), indicating ON–cell dominance. An intravitrreal injection of BDNF+CNTF+forskolin (BCF) increased the number of regenerated RGCs, but it increased also the ratio into 6.94 (ON 87%: OFF 13%). Numbers of ON– and OFF–cells were estimated as 2,149 +/ –777 (ON) and 895 +/– 606 (OFF) in the control retinas whereas 5,766 +/– 1215 (ON) and 858 +/– 234 (OFF) in the BCF–injected retina, indicating no increase of OFF–cells in the BCF–injected retina. Intravitreally injected nipradilol increased the ratio into 1.60 (ON 62%: OFF 38%), which was very close to that in the normal retina. In nipradilol–injected retinas, the numbers of regenerated RGCs were 11,518 +/– 1,159 (ON) and 7,330+/–1477 (OFF), which showed equal promotion by nipradilol in axonal regeneration of ON– and OFF–RGCs. When the cats were reared in light deprivation, the ratio was 3.58 (ON 78%: OFF 22%); no promotion of regeneration of OFF–center cells.
Conclusions: :
OFF–center RGCs had smaller ability to regenerate their axons along grafted peripheral nerves, and was not promoted with an injection of BCF. Nipradilol equally promoted regeneration of ON– and OFF–center RGCs.
Keywords: ganglion cells • regeneration • nitric oxide