Intraorbital Optic Nerve Crush Induces Retinal Ganglion Cell Loss: Transient Protection With the Neurotrophic Factors BDNF, NT–4 or CNTF

Abstract

Abstract: : Purpose: To investigate retinal ganglion cell (RGC) survival after complete intraorbital optic nerve crush (IONC) and administration of the neurotrophic factors Ciliary neurotrophic factor (CNTF), Brain derived neurotrophic factor (BDNF) and Neurotrophin–4 (NT–4). Methods: Adult Sprague–Dawley rats were anaesthetized and retinal ganglion cells (RGC) were retrogradely labelled with Fluorogold (3% fluorogold in 0.9% NaCl containing 10% DMSO) applied to both superior colliculi (SCi). Seven days later, the left optic nerve was exposed and completely crushed with fine angulated jeweller's forceps, at approximately 3 mm from the optic disc. Right after crush, several groups of rats received an intravitreal injection of vehicle or the following trophic factors: (5µl of PBS), 5µg of BDNF, 5 µg of NT–4 or 5µg of CNTF. RGC survival was assessed 5, 7, 9 or 12 days after injury by counting FG–labelled RGCs in twelve standard regions of the left (axotomized) and right (intact) retinas. Results: Five, 7, 9 or 12 days after complete intraorbital optic nerve crush (IONC), the mean (±SD) densities of FG–labelled RGCs in the left axotomized retinas represented 92% (n=8), 80% (n=14), 49% (n=8) or 32% (n=11), respectively, of the contralateral intact retinas. Significant cell loss was observed between 5 and 7 days after injury. Intravitreal administration of BDNF, NT–4 or CNTF resulted in RGC survival rates of 95% (n=7), 89% (n=7) or 91% (n=8), respectively, by 7 days after injury and in survival rates of 67% (n=5), 60% (n=8) or 36% (n=7), respectively, by 12 days after injury. Conclusions: Intraorbital optic nerve crush results in RGC loss that first appears between 5 and 7 days after the lesion, progresses during the period of the study and causes death of approximately 70% of the RGC population by 12 days after injury. Prevention of IONC–induced RGC death was observed at 7 days with BDNF, NT–4 or CNTF. This neuroprotection was transient, and by 12 days after IONC only BDNF or NT–4 showed significant neuroprotection.

Keywords: ganglion cells • neuroprotection • neuro-ophthalmology: optic nerve