IntroductionThe entorhinal cortex has been shown to be involved in high-level cognitive functions in terrestrial mammals. It can be divided into two main areas: the lateral entorhinal area (LEA) and the medial entorhinal area (MEA). Understanding of its structural organization in cetaceans is particularly important given the extensive evidence for their cognitive abilities. The present study describes the cytoarchitectural and immunohistochemical properties of the entorhinal cortex of the bottlenose dolphin (Tursiops truncatus, Montagu, 1821), perhaps the most studied cetacean species and a paradigm for dolphins and other small cetaceans.MethodsFour bottlenose dolphins’ entorhinal cortices were processed. To obtain a precise overview of the organization of the entorhinal cortex we used thionin staining to study its laminar and regional organization, and immunoperoxidase technique to investigate the immunohistochemical distribution of three most commonly used calcium-binding proteins (CBPs), calbindin D-28k (CB), calretinin (CR) and parvalbumin (PV). Entorhinal cortex layers thickness were measured, morphological and morphometric analysis for each layer were conducted and statistically compared.ResultsSix layers in both the LEA and MEA were identified. The main difference between the LEA and the MEA is observed in layers II and III: the neurons in layer II of the LEA were denser and larger than the neurons in layer II of MEA. In addition, a relatively cell-free zone between layers II and III in LEA, but not in MEA, was observed. The immunohistochemical distribution of the three CBPs, CB, CR and PV were distinct in each layer. The immunostaining pattern of CR, on one side, and CB/PV, on the other side, appeared to be distributed in a complementary manner. PV and CB immunostaining was particularly evident in layers II and III, whereas CR immunoreactive neurons were distributed throughout all layers, especially in layers V and VI. Immunoreactivity was expressed by neurons belonging to different morphological classes: All CBPs were expressed in non-pyramidal neurons, but CB and CR were also found in pyramidal neurons.DiscussionThe morphological characteristics of pyramidal and non-pyramidal neurons in the dolphin entorhinal cortex are similar to those described in the entorhinal cortex of other species, including primates and rodents. Interestingly, in primates, rodents, and dolphins, most of the CBP-containing neurons are found in the superficial layers, but the large CR-ir neurons are also abundant in the deep layers. Layers II and III of the entorhinal cortex contain neurons that give rise to the perforant pathway, which conveys most of the cortical information to the hippocampal formation. From the hippocampal formation, reciprocal projections are directed back to the deep layer of the entorhinal cortex, which distributes the information to the neocortex and subcortical area. Our data reveal that in the dolphin entorhinal cortex, the three major CBPs label morphologically heterogeneous groups of neurons that may be involved in the information flow between entorhinal input and output pathways.

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宽吻海豚内嗅皮层钙结合蛋白免疫反应性的分布

简介内嗅皮层已被证明参与陆地哺乳动物的高级认知功能。它可以分为两个主要区域：外侧内嗅区（LEA）和内侧内嗅区（MEA）。鉴于有大量证据表明鲸类动物的认知能力，了解鲸类动物的结构组织尤为重要。本研究描述了宽吻海豚内嗅皮层的细胞结构和免疫组织化学特性（元宝斑鸠，Montagu，1821），可能是研究最多的鲸目动物物种，也是海豚和其他小型鲸目动物的范例。方法对四只宽吻海豚的内嗅皮质进行了处理。为了获得内嗅皮质组织的精确概述，我们使用硫堇染色来研究其层状和区域组织，并使用免疫过氧化物酶技术来研究三种最常用的钙结合蛋白（CBP）钙结合蛋白 D-28k（ CB）、钙结合蛋白（CR）和小清蛋白（PV）。测量内嗅皮层厚度，对各层进行形态学和形态测量分析并进行统计比较。结果LEA和MEA均识别出6层。 LEA 和 MEA 之间的主要区别在第 II 层和第 III 层中观察到：LEA 第 II 层中的神经元比 MEA 第 II 层中的神经元更密集且更大。此外，在 LEA 中观察到第 II 层和第 III 层之间有一个相对无细胞的区域，但在 MEA 中却没有。 CB、CR 和 PV 三种 CBP 的免疫组织化学分布在各层中不同。一侧 CR 和另一侧 CB/PV 的免疫染色模式似乎以互补方式分布。 PV和CB免疫染色在II层和III层中特别明显，而CR免疫反应性神经元分布在所有层中，特别是在V层和VI层中。属于不同形态类别的神经元表达免疫反应性：所有CBP均在非锥体神经元中表达，但CB和CR也在锥体神经元中发现。讨论海豚内嗅皮层锥体和非锥体神经元的形态特征类似于其他物种（包括灵长类动物和啮齿类动物）的内嗅皮层中描述的那些。有趣的是，在灵长类动物、啮齿类动物和海豚中，大多数含有 CBP 的神经元都存在于浅层，但大型 CR-ir 神经元在深层也很丰富。内嗅皮层的第二层和第三层包含产生穿通通路的神经元，该通路将大部分皮层信息传递到海马结构。从海马结构开始，相互投射被引导回内嗅皮层的深层，该深层将信息分发到新皮层和皮层下区域。我们的数据显示，在海豚内嗅皮层中，三个主要的 CBP 标记了形态异质的神经元组，这些神经元可能参与内嗅输入和输出通路之间的信息流。