Visual information in birds is to great extent processed in the optic tectum (TeO), a prominent laminated midbrain structure. Retinal input enters the TeO in its superficial layers, while output is limited to intermediate and deeper layers. In addition to visual information, the TeO receives multimodal input from the auditory and somatosensory pathway. The TeO gives rise to a major ascending tectofugal projection where neurons of tectal layer 13 project to the thalamic nucleus rotundus, which then projects to the entopallium. A second tectofugal projection system, called the accessory pathway, has however not been studied as thoroughly. Again, cells of tectal layer 13 form an ascending projection that targets a nucleus known as either the caudal part of the nucleus dorsolateralis posterior of the thalamus (DLPc) or nucleus uveaformis (Uva). This nucleus is known for multimodal integration and receives additional input from the lateral pontine nucleus (PL), which in turn receives projections from layer 8-15 of the TeO. Here, we studied a particular cell type afferent to the PL that consists of radially oriented neurons in layer 9. We characterized these neurons with respect to their anatomy, their retinal input, and the modulation of retinal input by local circuits. We found that comparable to other radial neurons in the tectum, cells of layer 9 have columnar dendritic fields and reach up to layer 2. Sholl analysis demonstrated that dendritic arborization concentrates on retinorecipient layers 2 and 4, with additional arborization in layers 9 and 10. All neurons recorded in layer 9 received retinal input via glutamatergic synapses. We analyzed the influence of modulatory circuits of the TeO by application of antagonists to γ-aminobutyric acid (GABA) and acetylcholine (ACh). Our data show that the neurons of layer 9 are integrated in a network under strong GABAergic inhibition, which is controlled by local cholinergic activation. Output to the PL and to the accessory tectofugal pathway thus appears to be under strict control of local tectal networks, the relevance of which for multimodal integration is discussed.

中文翻译：

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鸡视直肠癌第9层神经元的解剖学和生理学。

鸟类的视觉信息在很大程度上是由显眼的叠层中脑结构-光学盖（TeO）处理的。视网膜输入在其表层进入TeO，而输出则限于中间层和深层。除视觉信息外，TeO还从听觉和体感途径接收多模式输入。TeO引起一个主要的上升的睑板内投射，其中第13层的神经元投射到圆形丘脑核，然后投射到上皮。然而，还没有对彻底的第二种成虫投射系统（称为附属途径）进行研究。同样，顶盖层13的细胞形成一个上升的突起，该突起以被称为丘脑后侧背外侧核的尾部（DLPc）或葡萄膜核（Uva）的核为目标。该核已知用于多峰整合，并且从侧脑桥核（PL）接收其他输入，而脑桥侧核又接收来自TeO层8-15的投影。在这里，我们研究了PL传入的特定细胞类型，该细胞类型由第9层中的放射状神经元组成。我们就这些神经元的解剖结构，视网膜输入以及局部电路对视网膜输入的调制进行了表征。我们发现，与盖层中的其他放射状神经元相比，第9层的细胞具有柱状树突状区域并到达第2层。肖尔分析表明，树突状的乔化作用集中在视网膜受体第2层和第4层，第9层和第10层具有附加的树状化作用。第9层中记录的所有神经元均通过谷氨酸能突触接收视网膜输入。我们通过应用拮抗剂对γ-氨基丁酸（GABA）和乙酰胆碱（ACh）来分析TeO调节电路的影响。我们的数据表明，第9层的神经元在强大的GABA能抑制下被整合到网络中，而GABA能抑制是由局部胆碱能激活控制的。因此，向PL和向附生植物的粪便途径的输出似乎在本地的直肠网络的严格控制下，讨论了其与多峰整合的相关性。