Effects of different neurotrophic factors on the survival of retinal ganglion cells after a complete intraorbital nerve crush injury: A quantitative in vivo study

We examined in adult Sprague Dawley rats the loss of retinal ganglion cells (RGCs) induced by complete intraorbital optic nerve crush (IONC) as well as the effects of several neurotrophic factors to prevent IONC-induced RGC loss. Completeness of the IONC lesion was assessed by investigating the orthograde and retrograde transport of neuronal tracers applied to the origin and termination of the retinotectal pathway. RGC survival after IONC alone or combined with intraocular injection of the neurotrophic factors NT-4, BDNF or CNTF was quantified at survival intervals ranging from 5 to 12 days post-lesion (dpl) by identifying RGCs that had been pre-labelled with fluorogold (FG). RGC loss first appeared at 7 dpl and by 12 dpl only 32% of the RGC population remained in the retina. Intraocular administration of NT-4, BDNF or CNTF resulted in almost a complete protection against IONC-induced RGC loss by 7 dpl, and the protection remained significant by 12 dpl only for NT-4 and BDNF. We have analyzed these results taking into account our previous studies on the loss of RGCs induced by intraorbital optic nerve transection (IONT) and concluded that RGC loss induced by IONC is slower and less severe than that following IONT. Moreover, as for IONT-induced RGC loss, IONC-induced RGC loss may also be prevented with administration of NT-4, BDNF or CNTF, though for NT-4 and CNTF their neuroprotective effects differ depending on the injury type. Overall this data underscore the importance of the type of ON injury on the pattern of RGC degeneration as well as in their response to neuroprotective treatments.