Dosage dependence of the effect of Ginkgo biloba on the rat retinal ganglion cell survival after optic nerve crush

Purpose To investigate the dosage dependence of the Ginkgo biloba effect on retinal ganglion cell survival in the rat optic nerve crush model. Methods The study included 56 Sprague-Dawley rats, the right optic nerve of which was crushed in a standardized manner. Two hours after the crush and once daily during the follow-up, the animals received intragastral applications of saline (saline group; n=13), or of a G. biloba extract of 0.25% concentration (n=14; low-dosage group), 1% concentration (n=15; medium-dosage group), or 4% concentration (n=14; high-dosage group). At 23 days after the optic nerve crush, the retinal ganglion cells were retrogradely labelled by injecting 3% fluorogold into the superior colliculi of the brain. At 4 weeks after baseline, the animals were killed. Retinal flat mount photographs were assessed for number and density of the retinal ganglion cells. Results The mean survival rate defined as the ratio of retinal ganglion cell density in the right eye with optic nerve crash divided by the retinal ganglion cell density in left eye without optic nerve intervention increased significantly (P<0.001) from 58.4 +/- 9.0% in the saline group to 68.5 +/- 5.7% in the low-dosage group, to 73.7 +/- 6.4% in the medium-dosage group, and to 74.2 +/- 6.8% in the high-dosage group. Conclusions Intragastral applications of a G. biloba extract applied after an experimental and standardized optic nerve crush in rats were associated with a higher survival rate of retinal ganglion cells in a dosage-dependent manner. Eye (2009) 23, 1598-1604; doi:10.1038/eye.2008.286; published online 26 September 2008