Atoji Yasuro, Sarkar Sonjoy, Wild J Martin
Laboratory of Veterinary Anatomy, Faculty of Applied Biological Sciences, Gifu University, Gifu, Japan.
Department of Anatomy and Medical Imaging, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.
J Comp Neurol. 2018 Jan 1;526(1):146-165. doi: 10.1002/cne.24328. Epub 2017 Sep 28.
The visual 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). HD also connects with the hippocampus and olfactory system. Because HD is subjacent to HI, the two have been treated as one structure in many studies, and the fiber connections of HD have been examined by afferents and efferents originating outside HD. However, to clarify the difference between these two layers, they need to be treated separately. In the present study, the fiber connections of HD and 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 injected in HD, a major reciprocal connection was seen with the dorsolateral subdivision (DL) of the hippocampal formation. When CTB and BDA were bilaterally injected in HI, strong reciprocal connections were found between HI and HA. Next, projection neurons in HD and HI were examined by double staining for CTB combined with vesicular glutamate transporter 2 (vGluT2) mRNA in situ hybridization. After CTB was injected in DL or HA, many neurons revealed CTB+/vGluT2+ in HD or HI, respectively. Furthermore, in situ hybridization showed that DL and HA contained neurons expressing various subunits of ionotropic glutamate receptors: AMPA, kainate, and NMDA types. These results suggest that glutamatergic neurons in HD and HI project primarily to DL and HA, respectively.
上纹状体的顶部（HA）、HA的间质部分（IHA）、上纹状体的插入部分（HI）和上纹状体的致密细胞部分（HD）。HD还与海马体和嗅觉系统相连。由于HD位于HI下方，在许多研究中这两者被视为一个结构，并且HD的纤维连接已通过源自HD外部的传入和传出纤维进行了研究。然而，为了阐明这两层之间的差异，需要将它们分开处理。在本研究中，使用霍乱毒素B亚基（CTB）注射进行逆行追踪和生物素化葡聚糖胺（BDA）注射进行顺行追踪相结合的示踪技术，分析了HD和HI的纤维连接。当在HD双侧注射这两种示踪剂时，观察到与海马结构的背外侧亚区（DL）有主要的相互连接。当在HI双侧注射CTB和BDA时，发现HI与HA之间有强烈的相互连接。接下来，通过CTB双重染色结合囊泡谷氨酸转运体2（vGluT2）mRNA原位杂交检查HD和HI中的投射神经元。在DL或HA注射CTB后，许多神经元分别在HD或HI中显示为CTB+/vGluT2+。此外，原位杂交显示DL和HA含有表达离子型谷氨酸受体各种亚基的神经元：AMPA、海人酸和NMDA型。这些结果表明，HD和HI中的谷氨酸能神经元分别主要投射到DL和HA。
