Cataractogenic lens injury prevents traumatic ganglion cell death and promotes axonal regeneration both in vivo and in culture

PURPOSE. To examine and quantify neuroprotective and neurite-promoting acti vity on retinal ganglion cells (RGCs) after injury of the lens. METHODS. In adult albino rats, penetrating lens injury was performed by int raocular injection. To test for injury-induced neuroprotective effects in v ivo, fluorescence-prelabeled RGCs were axotomized by subsequent crush of th e optic nerve (ON) with concomitant lens injury to cause cataract. The numb ers of surviving RGCs were determined in retinal wholemounts and compared b etween the different experimental and control groups. To examine axonal reg eneration in vivo, the ON was cut and replaced with an autologous piece of sciatic nerve (SN). Retinal ganglion cells with axons that had regenerated within the SN under lens injury or control conditions were retrogradely lab eled with a fluorescent dye and counted on retinal wholemounts. Neurite reg eneration was also studied in adult retinal explants obtained either after lens injury or without injury. The numbers of axons were determined after 1 and 2 days in culture. Putative neurotrophins (NTs) were studied within im munohistochemistry and Western blot analysis. RESULTS. Cataractogenic lens injury performed at the same time as ON crush resulted in highly significant rescue of 746 +/- 126 RGCs/mm(2) (mean +/- S D; approximately 39% of total RGCs) 14 days after injury compared with cont rols without injury or with injection of buffer into the vitreous body (30 +/- 18 RGCs/mm(2)). When lens injury was performed with a delay of 3 days a fter ON crush, 49% of RGCs survived, whereas delay of 5 days still rescued 45% of all RGCs. In the grafting paradigm virtually all surviving RGCs afte r lens injury appeared to have regenerated an axon within the SN graft (763 +/- 114 RGCs/mm(2) versus 79 +/- 17 RGCs/mm(2) in controls). This rate of regeneration corresponds to approximately 40% of all RGCs. In the regenerat ion paradigm in vitro preceding lens injury and ON crush 5 days previous re sulted in a maximum of regeneration of 273 +/- 39 fibers/explant after 1 da y and 574 +/- 38 fibers/explant after 2 days in vitro. In comparison, in co ntrol retinal pieces without lens injury 28 +/- 13 fibers/explant grew out at 1 day, and 97 +/- 37 fibers/explant grew out at 2 days in culture. Immun ohistochemical and Western blot analysis of potential NTs in the injured le ns revealed no expression of ciliary neurotrophic factor (CNTF), brain-deri ved neurotrophic factor (BDNF), NT-4, nerve growth factor (NGF), and basic fibroblast growth factor (bFGF). CONCLUSIONS. The findings indicate that the lens contains high neuroprotect ive and neuritogenic activity, which is not caused by NT. Compared with the data available in the literature, this neuroprotection is quantitatively a mong the highest ever reported within the adult rat visual system.