Parameters of optic nerve electrical stimulation affecting neuroprotection of axotomized retinal ganglion cells in adult rats.

We previously showed the enhancement of survival of retinal ganglion cells (RGCs) by electrical stimulation (ES) of the optic nerve (ON) stump in adult rats. To elucidate the mechanisms underlying the survival enhancement, we determined whether the neuroprotective effect of ES is affected by the following parameters: stimulation time, frequency of current pulses and starting of ES. ES for 10min immediately after ON transection was not effective in increasing the number of surviving RGCs 7 days after the transection, but that for 30min was effective. ES at 20Hz was the most effective, when applied just after axotomy. When the starting of ES to the ON was shifted either 3h after or 4h before the axotomy, the neuroprotective effect of ES was not observed. These results suggest that the electrical activation of RGCs and/or the transected ON interfere with early events after axotomy that leads to RGC death.