Ishihara Yoshihisa, Sato Fumi, Guinet Alix, Grosser Sabine, Vida Imre, Kubota Yoshiyuki, Takayama Chitoshi
Department of Anatomy, School of Medicine, Faculty of Medicine, Toho University, 5-21-16 Omori-Nishi, Ota, Tokyo 143-8540, Japan; Institute of Integrative Neuroanatomy, Charité - Universitätsmedizin Berlin, Charitéplatz 1, Berlin 10117, Germany; Supportive Center for Brain Research, Section of Electron Microscopy, Kubota Group, National Institute for Physiological Sciences, 5-1 Higashiyama Myodaiji, Okazaki, Aichi 444-8787, Japan; Department of Molecular Anatomy, School of Medicine University of the Ryukyus, Uehara 207, Nishihara, Okinawa 903-0213, Japan.
Department of Anatomy, School of Medicine, Faculty of Medicine, Toho University, 5-21-16 Omori-Nishi, Ota, Tokyo 143-8540, Japan.
Neuroscience. 2025 Mar 5;568:285-297. doi: 10.1016/j.neuroscience.2024.12.048. Epub 2025 Jan 2.
The subiculum is the main output part of the hippocampal formation and is important for learning and memory. According to connection studies, the distal and proximal regions of the subiculum project to brain regions related to spatial and emotional memories, respectively. Our previous morphological studies indicated that the ventral subiculum (vSub) consists of two regions, the distal subiculum (Sub1) and the proximal subiculum (Sub2), whereas the dorsal subiculum (dSub) seems to comprise only one region (Sub1). However, the connection studies have reported that the dSub contains two regions. Accordingly, we hypothesized that the dSub may indicate "one region" and "two regions" at different dorsoventral levels. To confirm this hypothesis, serial sections of the dSub were prepared and labeled for nitric oxide synthase and Purkinje cell protein 4 as markers dividing the subiculum. As a result, vSub showed two regions, Sub1 and Sub2, whereas the dorsal tip of the subiculum showed one region (Sub1), as shown in our previous studies. However, two regions were observed in the dorsal sections. Accordingly, the same dSub indicated a different number of regions at different observation levels. To avoid confusion, we propose dividing the subiculum into Sub1 and Sub2 by immunoreactivities for subicular markers, instead of a rough division into the distal/proximal parts or the dorsal/ventral parts. Furthermore, we confirmed that Sub2 projected to the lateral septum. This finding is consistent with the fact that the proximal-ventral subiculum are involved in emotional memory.
海马下脚是海马结构的主要输出部分，对学习和记忆很重要。根据连接研究，海马下脚的远端和近端区域分别投射到与空间记忆和情感记忆相关的脑区。我们之前的形态学研究表明，腹侧海马下脚（vSub）由两个区域组成，即远端海马下脚（Sub1）和近端海马下脚（Sub2），而背侧海马下脚（dSub）似乎只包含一个区域（Sub1）。然而，连接研究报告称dSub包含两个区域。因此，我们假设dSub在不同的背腹水平可能显示“一个区域”和“两个区域”。为了证实这一假设，我们制备了dSub的连续切片，并用一氧化氮合酶和浦肯野细胞蛋白4作为划分海马下脚的标记物进行标记。结果，vSub显示出两个区域，即Sub1和Sub2，而海马下脚的背侧尖端显示为一个区域（Sub1），正如我们之前的研究所显示的那样。然而，在背侧切片中观察到了两个区域。因此，同一个dSub在不同的观察水平显示出不同数量的区域。为避免混淆，我们建议通过海马下脚标记物的免疫反应性将海马下脚分为Sub1和Sub2，而不是粗略地分为远端/近端部分或背侧/腹侧部分。此外，我们证实Sub2投射到外侧隔。这一发现与近端腹侧海马下脚参与情感记忆这一事实相一致。
