Analysis of the circuit for visual information and its function on the avian retinotectal system

我们可以把所得结果归纳为以下三点。1)视网膜顶盖纤维终末与接受终末的树突相互交错形成大的突触复合体。(a)与猫、兔、仓鼠的上级丘的视纤维终末相比，鸡顶盖的视纤维终末前支的分支更为复杂。(b)鸡顶盖内视神经末梢的突触复合体比哺乳动物外侧膝状体内的肾小球复杂。(c)顶盖内的视神经末梢的突触复合体的大小比上级丘内的更为恒定。(d)树突状突触后元件的形态和大小比上级丘更易变化。2)视网膜神经节细胞层的P物质和乙酰胆碱受体阳性神经元分别向顶盖B层和F层发出轴突。前者神经节细胞胞体小，树突状分支简单而狭窄。在后者中，观察到两种以上的神经节细胞亚型。其中一种类型的细胞体较大，树枝状分支简单而宽。3)我们研究了双眼视觉的行为方法在鸡，收到一只眼睛的破坏在胚胎第4天。手术组和正常组鸡的黑珠命中率无显著差异。结果表明，鸟类的双眼视觉不一定需要两只眼睛。鸟类的双眼视觉很可能是由鸟类特有的视网膜顶盖系统完成的。

We can conclude the results obtained in three points as follows. 1) Retinotectal fiber terminals and the dendrites that receive the terminals formed interdigitation each other to shape large synaptic complexes. (a) Compared to the optic fiber terminals in the superior colliculus (cat, rabbit, hamster), arborization of preterminal branches of optic fibers in the chick tectum was more complex. (b) Synaptic complexes of the optic nerve terminals in the chick tectum were more complex than the glomerulus in the mammalian lateral geniculate body. (c) Sizes of the synaptic complexes of the optic fiber terminals in the tectum were more constant compared to those in the superior colliculus. (d) Shapes and sizes of dendritic postsynaptic elements were more variable than those in the superior colliculus. 2) Substance-P and acetylcholine receptor immunoreactive neurons in the retinal ganglion cell layer sent axons to the layer B and layer F of the chick tectum, respectively. Ganglion cells in the former has small somata with simple and narrow dendritic arborization. In the latter, more than two subtypes of ganglion cells were observed. One type of them had large somata with simple and broad dendritic arborization. 3) We studied the binocular vision by behavioral methods in chicks that received destruction of one eye on embryonic day 4. There was no significant difference in the rate of hit of black beads between the operated and normal chicks. The results suggest that the avian binocular vision would not necessarily require both eyes. Probably, the binocular vision in birds is carried out by the peculiar retinotectal system to birds.