CNR Neuroscience Institute, Pisa, 56124, Italy.
Save Sight Institute, Discipline of Clinical Ophthalmology, The University of Sydney, Sydney, NSW, 2000, Australia.
Sci Rep. 2018 Nov 6;8(1):16429. doi: 10.1038/s41598-018-34621-2.
The AII amacrine cell is known as a key interneuron in the scotopic (night-vision) pathway in the retina. Under scotopic conditions, rod signals are transmitted via rod bipolar cells to AII amacrine cells, which split the rod signal into the OFF (via glycinergic synapses) and the ON pathway (via gap junctions). But the AII amacrine cell also has a "day job": at high light levels when cones are active, AII connections with ON cone bipolar cells provide crossover inhibition to extend the response range of OFF cone bipolar cells. The question whether AII cells contribute to crossover inhibition in primate fovea (where rods and rod bipolar cells are rare or absent) has not been answered. Here, immunohistochemistry and three-dimensional reconstruction show that calretinin positive cells in the fovea of macaque monkeys and humans have AII morphology and connect to cone bipolar cells. The pattern of AII connections to cone bipolar cells is quantitatively similar to that of AII cells outside the fovea. Our results support the view that in mammalian retina AII cells first evolved to serve cone circuits, then later were co-opted to process scotopic signals subsequent to the evolution of rod bipolar cells.
AII 无长突细胞是视网膜视杆（暗视觉）通路中的一种关键中间神经元。在暗视觉条件下，杆状细胞信号通过杆状双极细胞传递至 AII 无长突细胞，AII 无长突细胞将杆状信号分裂为 OFF 通路（通过甘氨酸能突触）和 ON 通路（通过缝隙连接）。但是，AII 无长突细胞还有一个“日常工作”：在高光照水平下，当视锥细胞活跃时，AII 与 ON 视锥双极细胞的连接提供交叉抑制作用，以扩展 OFF 视锥双极细胞的反应范围。AII 细胞是否有助于灵长类动物中央凹（此处杆状细胞和杆状双极细胞很少或不存在）中的交叉抑制作用，这个问题尚未得到解答。本文通过免疫组织化学和三维重建表明，猕猴和人类中央凹中的 calretinin 阳性细胞具有 AII 形态，并与视锥双极细胞相连。AII 细胞与视锥双极细胞的连接模式在数量上与中央凹外的 AII 细胞相似。我们的结果支持了这样一种观点，即在哺乳动物视网膜中，AII 细胞最初是为了服务于视锥细胞回路而进化的，然后在杆状双极细胞进化之后，又被重新用于处理视杆信号。
