Electrophysiological And Morphological Properties Of Rat Retinal Ganglion Cells During Postnatal Development

Purpose: To establish the rat retinal slice patch clamp technique. To study the electrophysiological properties of rat retinal ganglion cells during postnatal development, including the passive membrane properties and the active membrane properties such as action potentials gengerated by deplorizing current injections. To discuss the relations between the functional properties and morphological properties of rat retinal ganglion cells.Methods: Retinal slices were prepared from 90 Wistar rats. Whole cell recordings were made from retinal ganglion cells of postanatal rats. The RMP,IR of RGCs and APs generated by deplorizing current injections were recorded. Retinal ganglion cells were stained by Lucifer Yellow or biocytin which were injected into cells during whole cell recordings for the purpose of morphological study of RGCs. The retinae of rats ranging in age from postnatal days P1 through P30 were examined by light microscope.Results: 1. Totally 112 retinal ganglion cells were recorded from postanatal rats ranging in age from postnatal days P7 through P30. Three different discharge patterns of RGCs in response to maintained depolarizing currents were recorded, which were single firing, transient firing and sustained firing. At a certain range, the relationship between injected current and spike frequency in retinal ganglion cells was found to be linear.2. The three RGC types clearly differed from one another in their membrane properties(P<0.05). The RMP and IR of single firing RGCs were significantly higher, and the amplitude were significantly lower than the other two types(P<0.05). Among the three types, the thresholds and spike width of Aps of single firing RGCs were the largest and that of sustained firing RGCs were the smallest(P<0.05). The maximum frequency of APs of sustained firing RGCs was significantly larger than that of transient firing RGCs(P<0.01).3. During a relatively brief developmental period(postnatal days P7-P30), retinal ganglion cells of rats exhibited pronounced changes in the discharge patterens(P<0.01) generated by depolarizing current injections. The percentage of single firing RGCs decreased from 50.0% in P7-13 to zero in P21-30. By contrast, the percentage of sustainedfiring RGCs increased from 23.5% in P7-13 to 69.2% in P28-30, and that of transient firing RGCs decreased slightly. 4. The membrane properties of rat retinal ganglion cells changed significantly during development. With age, the RMP, IR and the threshold of Aps of RGCs decreased , and the amplitude of APs of RGCs increased, and the steady state frequency of APs of sustained firing RGCs increased(P<0.01), and then reached a stable level after eye opening. There were significant differences between before-eye-open group(P7-13) and after-eye-open group(P14-30)(P<0.01), but no significant differences among the groups after eye opening. Following grow up, the spike width of APs of the three RGC types decreased and the maximum frequency of APs of transient firing and sustained firing RGCs increased. There were significant differences between each group(P<0.05).5. There were only the RPE layer, the neuroblast layer and the ganglion cell layer in rat reinae till postnatal day 3. Following grow up, the retinae developed gradually. The rat retinae would be mature nearly on postnatal days 21.6. Totally 29 retinal ganglion cells of rats were stained by Lucifer Yellow or biocytin. Among which, the discharge patterns of RGCs changed with age. In P7-13, the percentage of single firing, transient firing and sustained firing RGCs were 50.0%,30.0% and 20.0% receptively. In P14-30, none of single firing RGCs could be seen and the percentage of transient firing and sustained firing RGCs were 47.4% and 52.6% respectively. Among the 24 RGCs labeled by Lucifer Yellow, the soma diameters of transient firing and sustained firing RGCs were larger than that of single firing RGCs(P<0.05), and that of transient and sustained RGCs were not significantly different. The soma diameters of 80.0% single firing and 55.6% susta...