Zhang Jian, Zhang Ai-Jun, Wu Samuel M
Cullen Eye Institute, Baylor College of Medicine, Houston, Texas 77030, USA.
J Comp Neurol. 2006 Nov 20;499(3):432-41. doi: 10.1002/cne.21116.
By using immunocytochemical techniques, we demonstrate that there are two distinct, nonoverlapping populations of horizontal cells (HCs) in the tiger salamander retina: GABA-positive cells account for about 72% and GABA-negative (calretinin-positive) cells account for 28% of the total HC somas. The calretinin-positive HCs have relatively sparse and thick dendrites: soma diameter of 19.72 +/- 0.29 microm, and soma density of 140 +/- 13 cells/mm(2), morphological features very much like the A-type HCs described in the accompanying article. The GABA-positive HCs have thinner dendritic and coarse axon-terminal-like processes of higher density: soma diameter of 18 +/- 0.18 microm, and soma density of 364 +/- 18 cells/mm(2), features that very much resemble the B-type HCs and B-type HC axon terminals in the accompanying article. By using double and triple immunostaining techniques we found that only 18% of the non-GABAergic HC dendritic clusters contact rods, whereas the remaining 82% of the dendritic clusters contact cones. This is consistent with the physiological finding in the accompanying article that the A-type HCs are cone-dominated. On the other hand, 32% of GABAergic HC dendrites contact rod pedicles and 68% contact cone pedicles, consistent with the physiological finding that B-type HCs and B-type HC axon terminals receive mixed rod/cone inputs. Detailed confocal microscope analysis shows that 4% rods, 6% principal double cones/single cones, and 100% accessory double cones contact calretinin-positive HCs, and 79% rods, 100% principal double cones, 14% accessory double cones, and 82% single cones contact GABAergic HCs. These results suggest that GABAergic and non-GABAergic HC input/output synapses differ and they may mediate different functional pathways in the outer retina.
通过免疫细胞化学技术，我们证明在虎螈视网膜中存在两种不同的、不重叠的水平细胞（HCs）群体：GABA阳性细胞约占HCs胞体总数的72%，GABA阴性（钙视网膜蛋白阳性）细胞占28%。钙视网膜蛋白阳性的HCs具有相对稀疏且粗大的树突：胞体直径为19.72±0.29微米，胞体密度为140±13个细胞/平方毫米，其形态特征与随附文章中描述的A型HCs非常相似。GABA阳性的HCs具有较细的树突和密度较高的粗大轴突终末样突起：胞体直径为18±0.18微米，胞体密度为364±18个细胞/平方毫米，这些特征与随附文章中的B型HCs和B型HCs轴突终末非常相似。通过使用双重和三重免疫染色技术，我们发现只有18%的非GABA能HC树突簇与视杆细胞接触，而其余82%的树突簇与视锥细胞接触。这与随附文章中的生理学发现一致，即A型HCs以视锥细胞为主。另一方面，32%的GABA能HC树突与视杆小足接触，68%与视锥小足接触，这与生理学发现一致，即B型HCs和B型HCs轴突终末接受视杆/视锥混合输入。详细的共聚焦显微镜分析表明，4%的视杆细胞、6%的主要双视锥细胞/单视锥细胞和1杯细胞接触钙视网膜蛋白阳性的HCs，79%的视杆细胞、100%的主要双视锥细胞、14%的辅助双视锥细胞和82%的单视锥细胞接触GABA能HCs。这些结果表明，GABA能和非GABA能HC的输入/输出突触不同，它们可能在外层视网膜中介导不同的功能通路。
