Abstract
Abstract: :
Purpose: To elucidate the role of glycine receptor in the maturation of ON–OFF pathway, the dendritic stratification pattern of retinal ganglion cells (GCs) in inner plexiform layer (IPL) was examined in both wild type and spastic mutant mice, in which the density of glycine receptors is reduced about 80% in the nervous system. Methods: Retinas with Thy1–YFP (+) GCs were immuno–labeled with antibody against GFP to enhance YFP signal. Z–stack images were collected at a step of 0.5 µm using confocal laser–scanning microscope. The dendritic stratification of each GC was characterized by their ramification depth and thickness in IPL. Results:GCs of 167 in wild type and 114 in spastic mutant mice were studied and classified into 4 groups based on their dendritic stratification pattern in IPL. The dendrites of bistratified ON–OFF GCs were clearly separated into 2 layers and ramified in sublamina a and b of IPL, respectively. Subpopulation of GCs ramified their dendrites close to the center of IPL and extended into both sublamina a and b. These cells may receive signal inputs from both ON and OFF bipolar cells and therefore were classified as monostratified ON–OFF GCs. Cells with their dendrites exclusively ramified in either sublamina a or b were classified as ON or OFF GCs, respectively. The population of bistratified ON–OFF GCs was decreased from 22.2 ± 5.3 % in wild type to 13.2 ± 6.8 % in spastic mutant mice (P < 0.05). The population of OFF GCs in spastic mutant mice (14.2 ± 6.9 %) was also decreased in comparison with wild type (24.2 ± 6.4 %, P < 0.05). In contrast, the percentage of the monostratified ON–OFF GCs was significantly higher in spastic mutation (30.0 ± 8.7 %) than that of wild type control (11.6 ± 2.8 %, P < 0.01). The dendrites of monostratified ON–OFF GCs in spastic mice were more diffusely ramified in IPL (occupy 25.6 ± 7.0 % of the total thickness of IPL) than that of wild type control (occupy 15.0 ± 3.9 % of the total thickness of IPL, P < 0.001). For ON GCs, however, neither the percentage nor the dendritic stratification pattern in spastic mutant mice was statistically different from that of wild type controls. There were 42.6 ± 3.8 % ON GCs in wild type and 42.0 ± 8.8 % in spastic mutant mice (P > 0.05). The average dendritic stratification width was 15.6 ± 2.8 % and 16.5 ± 4.0 % of the total thickness of the IPL for wild type and spastic mutant mice, respectively (P > 0.05). Conclusions:The decreasing of the population of OFF and bistratified ON–OFF GCs in spastic mice suggest that mutation of glycine receptors retarded the maturation of OFF pathway in mouse retina and resulted in an correspond increasing of GCs with their dendrites more diffusely ramified in IPL.
Keywords: retina: proximal (bipolar, amacrine, and ganglion cells) • retinal development • receptors