Abstract
Purpose :
The mature mammalian central nervous system fails to regenerate after severe injuries. However, it is known that the increased neural activity in mouse retinal ganglion cells (RGCs) by extrinsic stimulation can promote their axon growth. Recently, it has been shown that using blue light to stimulate transgenic mice that channelrhodopsin-2 is expressed exclusively in RGCs can modulate neural activity and enhance neurite outgrowth of postnatal retinal explants. In the mammalian retina, there are intrinsic photosensitive retinal ganglion cells (ipRGCs), thus blue light stimulation may also activate this subset of RGCs and promote axon growth. In the present study, the aim was to examine whether activating ipRGCs alone can induce the neurite outgrowth of postnatal explants.
Methods :
Retinal explants from P11 wild type mice were stimulated with different frequencies of blue light LED for one hour to activate ipRGCs and then cultured for 5 days. The extent of neurite outgrowth was quantified and compared to determine the effect of ipRGC activation on axon regeneration. Multi-electrode array was also used to examine the neural activity patterns of retinal explants upon blue light stimulation.
Results :
The results showed that activation of ipRGCs by blue light stimulation with the 1/60 Hz temporal pattern (30 s “on” and 30 s “off”) for one hour at the beginning of the experiment can significantly enhance neurite outgrowth of retinal explants in P11 wild type mice. While the number of ipRGCs is low in the developing retina, the fact that there are extensive gap junction couplings among ipRGCs and other types of RGCs which allows the spread neural activity across the whole of the retina and thus manifests the effect of blue light stimulation on neurite outgrowth. It was also found that blocking the stage II retinal waves during 1/60 Hz blue light stimulation significantly reduced neurite outgrowth of retinal explants in P11 mice, suggesting that endogenous correlated waves provide the most important neural activity to the neurite outgrowth.
Conclusions :
Thus, the present findings demonstrate that ipRGCs play a key role in facilitating the neurite outgrowth of retinal explants in the developing retina and stage II retinal waves are an indispensable component in promoting neurite regeneration.
This is a 2020 ARVO Annual Meeting abstract.