The Effect Of Glutamate On Retinal Ganglion Cells During Retinal Remodeling In RCS Rats

ObjectiveTo study the influence of glutamate on the survival of RGCs, and the RGCselectrophysiological function during retinal degeneration in RCS rats, through researches ofthe releasing, uptaking, conversion of glutamate during the retinal remodeling, and theeffect of retinal information output changes of glutamate as neurotransmitter on the RGCsfunction, so as to provide theoretical fundation for neuron protection,vision function rescueand reconstruction during retinal degeneration.MethodsThe expression levels of VGLUT-1(vesicular glutamate transporter1) and PKCα(Protein kinase C) were respectively detected in RCS rat and wild-type rat retinas at postnatal15day (P15), P30, P60, P90by quantitive real time PCR and immunohistochemisty.Glutamine synthetase (GS) and L-glutamate/L-aspartate transporter (GLAST) wereevaluated by western blot at same time points. And the patch clamp technique was used tomeasure the change of electrophysiological function of RGCs during retinal degeneration inRCS rats and wild-type rats.Results1. The photoreceptor cells lost firstly in RCS rats during retinal degeneration, and theratio of survival bipolar cells in inner plexiform layer to whole retinal cells graduallyincreased. At the terminal stage of retinal degeneration, there were still a lot of neurons ininner nuclear layer and ganglion cell layer.2. The releasing of glutamate as neurotransmitters gratually raised till the middle stageof retinal degeneration in RCS rats. And the uptaking of glutamate in Müller cells did notaccordingly increased, but the conversion of glutamate enhanced in Müller cells. At thefinal stage of retinal degeneration, the volume of glutamate release decrease relatively.3. The inward current of wild-type rats’ RGCs evoked by light, clamp at-80mV, consist of the AMPA receptor element, the GABA receptor element, the Na+inflow afteraction potential evoked by light. At this clamp voltage, the RGCs accepted the message ofsuperior neurons with AMPA receptor and GABA receptor. The current strength of inwardcurrent evoked by light did not change at different time point. The glutamate current did notchange yet. And the NBQX did not influence the time course of those inward current.4. The survival RGCs in RCS rats, which can not evoked by light, still reserved theelectrophysiological function partly. At the early stage of retinal degeneration, partial RGCshad appeared functional impairment, the spike could not transmit to RGCs through superiorneurons. Up to the terminal stage of retinal degeneration, all kind of suvival RGCs couldnot accept the message from superior neurons at all.5. ON-type RGCs disfunction appeared at early stage of retinal dengeration in RCSrats, for instance, the course of information transmission delayed, the function of receivingand processing the message from superior neurons descended, and the time of retinalinformation output delayed. But those function of OFF-type and ON-OFF-type RGCs didnot be impacted. At the terminal stage of retinal degeneration, there were no visual signaloutput in RCS rats’ retina.6. The volume of receiving and processing the message from superior neurons in RCSrats were lower than that of wild-type rats. And those message transmission passed throughthe postsynaptic excitatory current.Summary1. There have a lot of survival neurons in RCS rats at the terminal stage of retinaldegeneration. It provided the theoretical dundation for some treatment, such asphotoreceptor cell and visual prosthesis transplant, in order to rescue the visual function.2. The glutamate in the RCS rats’ retina at the middle stage of degenerationaccumulated likely. Till the final stage of degeneration, the intrinsic glutamatergic drive ofthe sensory retina to inferior neurons decreased. It support the hypothesis that thedeafferentation activates retinal remodeling.3. With the development of retinal degeneration, the RGCs of RCS rats graduallybrought about disfunction, and could not receive the singal input from superior neurons, sothat it could not export signal to the center visual system. But the suvival RGCs that can not evoked by light still reserved the partial electrophysiological function. This provide thetheoretical and experimental fundation for resecue the visual function after retinalremodeling.