Laboratory of Veterinary Anatomy, Faculty of Applied Biological Sciences, Gifu University, Gifu 501-1193, Japan.
Department of Anatomy and Medical Imaging, Faculty of Medical and Health Sciences, University of Auckland, Auckland 92019, New Zealand.
Brain Res. 2019 May 15;1711:130-139. doi: 10.1016/j.brainres.2019.01.001. Epub 2019 Jan 2.
The Wulst in birds shows a four-layered structure: apical part of the hyperpallium (HA), interstitial part of HA (IHA), intercalated part of hyperpallium (HI), and densocellular part of hyperpallium (HD). The Wulst consists of a small rostral somatosensory region and a larger caudal visual region. The visual HD relays visual information to IHA and HA in the Wulst and also transfers visual information to the hippocampal formation (Atoji et al., J Comp Neurol 526: 146-165, 2018). However, fiber pathways of the rostral HD remain unknown. In the present study, the fiber connections of the rostral HD and overlying HI were analyzed with tract-tracing techniques using a combination of injections of cholera toxin subunit B (CTB) for retrograde tracing and biotinylated dextran amine (BDA) for anterograde tracing. When the two tracers were bilaterally but separately injected into the rostral HD, major reciprocal connections were seen with the rostral HA, prepiriform cortex, and subdivisions of the hippocampal formation. One-way projections of huge fibers also reached the medial part of the medial striatum. When CTB and BDA were bilaterally and separately injected into the rostral HI, strong reciprocal connections were found between the rostral HI and HA, and weak connections were seen with areas outside the Wulst. These results suggest that the fiber pathways of the rostral HD and HI are distinguishable from each other in the telencephalon and suggest also that the rostral HD relays information to the rostral HA and simultaneously acts as a mediator to the hippocampal formation.
外端脑（HA）的顶部分，HA 的间质部分（IHA），外端脑的插入部分（HI）和外端脑的致密细胞部分（HD）。脑缘由一个较小的吻侧躯体感觉区和一个较大的尾侧视觉区组成。视觉 HD 将视觉信息中继到脑缘的 IHA 和 HA，并将视觉信息传递到海马结构（Atoji 等人，J Comp Neurol 526: 146-165, 2018）。然而，吻侧 HD 的纤维通路仍然未知。在本研究中，使用霍乱毒素亚单位 B（CTB）进行逆行示踪和生物素化葡聚糖胺（BDA）进行顺行示踪的组合，通过示踪技术分析了吻侧 HD 和覆盖的 HI 的纤维连接。当两种示踪剂分别双侧但分开注入吻侧 HD 时，与吻侧 HA、前梨状皮质和海马结构的细分区域观察到主要的相互连接。单向投射的巨大纤维也到达内侧纹状体的内侧部分。当 CTB 和 BDA 分别双侧且分开注入吻侧 HI 时，在吻侧 HI 和 HA 之间发现了强烈的相互连接，而与脑缘外部区域的连接较弱。这些结果表明，吻侧 HD 和 HI 的纤维通路在端脑中是可区分的，并且还表明吻侧 HD 将信息中继到吻侧 HA，并同时作为海马结构的中介。
