Perin Paola, Cossellu Daniele, Vivado Elisa, Batti Laura, Gantar Ivana, Voigt Fabian F, Pizzala Roberto
Department of Brain and Behaviour Sciences, University of Pavia, Pavia, Italy.
Department of Molecular Medicine, University of Pavia, Pavia, Italy.
Front Neurol. 2024 May 16;15:1386654. doi: 10.3389/fneur.2024.1386654. eCollection 2024.
Calvarial bone marrow has been found to be central in the brain immune response, being connected to the dura through channels which allow leukocyte trafficking. Temporal bone marrow is thought to play important roles in relation to the inner ear, but is still largely uncharacterized, given this bone complex anatomy. We characterized the geometry and connectivity of rat temporal bone marrow using lightsheet imaging of cleared samples and microCT. Bone marrow was identified in cleared tissue by cellular content (and in particular by the presence of megakaryocytes); since air-filled cavities are absent in rodents, marrow clusters could be recognized in microCT scans by their geometry. In cleared petrosal bone, autofluorescence allowed delineation of the otic capsule layers. Within the endochondral layer, bone marrow was observed in association to the cochlear base and vestibule, and to the cochlear apex. Cochlear apex endochondral marrow (CAEM) was a separated cluster from the remaining endochondral marrow, which was therefore defined as "vestibular endochondral marrow" (VEM). A much larger marrow island (petrosal non-endochondral marrow, PNEM) extended outside the otic capsule surrounding semicircular canal arms. PNEM was mainly connected to the dura, through bone channels similar to those of calvarial bone, and only a few channels were directed toward the canal periosteum. On the contrary, endochondral bone marrow was well connected to the labyrinth through vascular loops (directed to the spiral ligament for CAEM and to the bony labyrinth periosteum for VEM), and to dural sinuses. In addition, CAEM was also connected to the tensor tympani fossa of the middle ear and VEM to the endolymphatic sac. Endochondral marrow was made up of small lobules connected to each other and to other structures by channels lined by elongated macrophages, whereas PNEM displayed larger lobules connected by channels with a sparse macrophage population. Our data suggest that the rat inner ear is surrounded by bone marrow at the junctions with middle ear and brain, most likely with "customs" role, restricting pathogen spread; a second marrow network with different structural features is found within the endochondral bone layer of the otic capsule and may play different functional roles.
颅盖骨骨髓已被发现是大脑免疫反应的核心，它通过允许白细胞运输的通道与硬脑膜相连。颞骨骨髓被认为在内耳方面发挥着重要作用，但鉴于该骨的复杂解剖结构，其仍在很大程度上未被充分描述。我们使用清除样本的光片成像和微型计算机断层扫描（microCT）对大鼠颞骨骨髓的几何形状和连通性进行了表征。通过细胞成分（特别是巨核细胞的存在）在清除的组织中识别骨髓；由于啮齿动物中不存在气腔，骨髓簇在微型计算机断层扫描中可通过其几何形状识别。在清除的岩骨中，自发荧光可用于勾勒耳囊层。在内软骨层内，观察到骨髓与耳蜗基部、前庭以及耳蜗顶端相关联。耳蜗顶端内软骨骨髓（CAEM）是与其余内软骨骨髓分离的簇，因此其余内软骨骨髓被定义为“前庭内软骨骨髓”（VEM）。一个大得多的骨髓岛（岩骨非内软骨骨髓，PNEM）延伸到围绕半规管臂的耳囊之外。PNEM主要通过与颅盖骨类似的骨通道与硬脑膜相连，只有少数通道指向管道骨膜。相反，内软骨骨髓通过血管环（CAEM指向螺旋韧带，VEM指向骨迷路骨膜）与迷路以及硬脑膜窦紧密相连。此外，CAEM还与中耳的鼓膜张肌窝相连，VEM与内淋巴囊相连。内软骨骨髓由通过由细长巨噬细胞排列的通道相互连接并与其他结构相连的小叶组成，而PNEM则显示出由通道连接的较大小叶，巨噬细胞数量稀少。我们的数据表明，大鼠内耳在与中耳和大脑的连接处被骨髓包围，很可能起到“海关”作用，限制病原体传播；在耳囊的内软骨骨层内发现了具有不同结构特征的第二个骨髓网络，可能发挥不同的功能作用。
