Behrens U D, Wagner H J
Anatomisches Institut, Universität Tübingen, Germany.
Vision Res. 1996 Dec;36(24):3901-11. doi: 10.1016/s0042-6989(96)00139-3.
We have investigated the effects of light and dark adaptation on the overall morphology of bipolar cell (BC) terminals in sublaminae a and b of the inner plexiform layer after labelling with Lucifer Yellow (LY) and PKC immunostaining using confocal laser scanning microscopy and serially sectioned material for electron microscopy. Three-dimensional reconstructed terminals showed marked adaptation-dependent changes of their morphology. Terminals of mixed rod-cone BCs in sublamina a (Ma BC) were irregular and scalloped in light adapted, but smooth and regular in dark-adapted specimens. Terminals from mixed rod-cone BCs in sublamina b (Mb BCs) exhibited an opposite behaviour. At the ultrastructural level, bipolar terminals in both sublaminae showed fingerlike extensions (spinules) invaginating presynaptic amacrine cell (AC) processes. Sixty-two percent of the dark-adapted Mb terminals in sublamina b showed spinules, whereas 21% of the light-adapted terminals had spinules. By contrast, 50.6% of the light-adapted Ma terminals in sublamina a formed spinules, compared to 17.8% of the dark-adapted Ma terminals in this sublamina. These observations reflect the functional subdivision of the inner plexiform layer in an inner ON-and an outer OFF-centre lamina. Our findings suggest that the synaptic plasticity of BC axon terminals may be due to differences of BC membrane potential, or the activity of AC input onto bipolar terminals. They may contribute to processes of fine tuning regulating the efficiency of AC-BC interaction under varying adaptation conditions.
我们使用共聚焦激光扫描显微镜，通过荧光黄（LY）标记和蛋白激酶C（PKC）免疫染色，并结合用于电子显微镜观察的连续切片材料，研究了明适应和暗适应对内网状层a和b亚层中双极细胞（BC）终末整体形态的影响。三维重建的终末显示出其形态明显的适应依赖性变化。a亚层中混合性视杆-视锥双极细胞（Ma BC）的终末在明适应时不规则且呈扇形，但在暗适应标本中则光滑且规则。b亚层中混合性视杆-视锥双极细胞（Mb BC）的终末表现出相反的行为。在超微结构水平上，两个亚层中的双极终末均显示出指状延伸（棘状突起），这些突起向突触前无长突细胞（AC）的突起内凹陷。b亚层中62%的暗适应Mb终末有棘状突起，而明适应终末中有21%有棘状突起。相比之下，a亚层中50.6%的明适应Ma终末形成了棘状突起，而该亚层中暗适应Ma终末只有17.8%形成棘状突起。这些观察结果反映了内网状层在内侧ON中心层和外侧OFF中心层的功能细分。我们的研究结果表明，双极细胞轴突终末的突触可塑性可能是由于双极细胞膜电位的差异，或者是双极终末上无长突细胞输入的活性不同所致。它们可能有助于在不同适应条件下微调调节无长突细胞-双极细胞相互作用效率的过程。
