Survival Enhancement of Axotomized Retinal Ganglion Cells by Electrical Stimulation to the Optic Nerve Depending on Stimulus Frequency, Period and Timing of Stimulation

Abstract

Purpose: : To elucidate the underlying mechanisms of survival promoting effect of electrical stimulation (ES) to the optic nerve (ON) stump on axotomized retinal ganglion cells (RGCs) in adult rats, we investigated here whether such neuroprotective effect of ES was affected by the following parameters: stimulation time and frequency, and timing when ES was delivered.

Methods: : Adult Wistar albino rats were used. RGCs were retrogradely pre-labeled with fluorogold^TM (FG), and then ON was transected intraorbitally. Before or after sectioning the ON, ES was applied to the ON right behind the grobe. One week after treatment, whole mounts of the retinas were prepared to determine the density of surviving RGCs, which were identified with FG using a epifluorescence microscopy.

Results: : By ES at 20Hz for 2 hrs applied to the ON stumps right after the ON transection, the mean density of surviving RGCs at 7 days after axotomy increased from 57% to 82% of intact retinas, confirming the previous study (Morimoto et al., 2002). Contrary to 20 Hz, ES at neither 10 nor 50 Hz enhanced the density of FG-labeled RGCs. ES at 20Hz after ON transection for 10 min was not effective in enhancing the density of surviving RGCs 7 days after the treatment, but that for 30 min was effective. ES at 20 Hz provided the highest density of surviving RGCs, when applied just after axotomy. When the time for stimulating the ON was shifted either 3 hrs after or 4 hrs before axotomy, the neuroprotective effect of ES was not observed. While the mean density of RGCs reduced to 19% of control retinas at 14 days after axotomy, 30% of normal RGCs were preserved in the stimulated retinas.

Conclusions: : The present study demonstrates that survival promoting effects of ES depended not only on current intensity, but also on duration of ES, and frequency of stimulation pulses. Taking these results with narrow time-window of ES around ON transection, ES might be used to intervene the early events of axotomy-induced RGC death by activating RGCs and/or the ON electrically.All procedures conformed to the ARVO statement for the Use of Animals in Ophthalmic and Vision Research.Commercial Relationship: Health Sciences Research Grants from the Ministry of Health, Labor and Welfare, Japan.

Keywords: neuroprotection • ganglion cells • cell survival