Lannoo M J, Maler L, Tinner B
Department of Anatomy, Faculty of Health Sciences, University of Ottawa, Ontario, Canada.
J Comp Neurol. 1989 Feb 15;280(3):331-42. doi: 10.1002/cne.902800302.
To determine the organizational principles underlying the peripheral electrosensory nervous system of weakly electric gymnotiform teleosts we labelled each of the four anterior lateral line nerve branches with HRP. We determined the position of labelled cell bodies within the ganglion and followed anterogradely filled fibers to their termination sites in one of the four somatotopic maps in the electroreceptive lateral line lobe (ELL). Within the ganglion, cell bodies exhibit a loose somatotopy based on nerve branch position: trunk electroreceptors have their cell bodies located in the caudal ganglion; cell bodies to the head receptors are rostral. Cell bodies to the head exhibit a rough dorsoventral polarity, supraorbital cells tend to be located dorsally, infraorbital cells centrally, and mandibular cells ventrally. Despite this general somatotopy there is substantial overlap (up to 30%) of cell bodies among regions. There appears to be no rostrocaudal topography within nerve branch regions. Iontophoretic WGA-HRP injected into the medial segment of the ELL retrogradely labelled cell bodies that innervate ampullary organs. These cell bodies were dispersed throughout the ganglion, indicating that cell bodies do not cluster by receptor type. Peripherally directed axons from the ganglion appear to undergo an active reorganization in order to form the nerve branches. Within nerve branches, axons to a particular area of skin do not cluster together. Centrally from the ganglion, axons retain the position of their cell body until they reach the ELL border. Once in the ELL, fibers become sorted in the deep fiber layer according to receptor type and the map they terminate in. This reorganization involves rearrangement of fascicles and axons within fascicles. In toto, proceeding from peripheral to central, the electrosensory periphery loses at least a portion of its receptor topography in the distal nerve and ganglion and then acquires both a functional and somatotopic organization after reaching the ELL; conceptually it is torn down and rebuilt again. From an ontogenetic perspective, axonal growth occurs from the ganglion outward; the fact that ganglion cell bodies are not highly organized while the receptors they innervate and their central processes are suggests that active axonal guidance mechanisms are involved.
为了确定弱电裸背电鳗目硬骨鱼外周电感应神经系统的组织原则，我们用辣根过氧化物酶（HRP）标记了四条前侧线神经分支中的每一条。我们确定了神经节内标记细胞体的位置，并顺行追踪充满标记物的纤维，直至它们在电感受侧线叶（ELL）的四个躯体定位图之一中的终止位点。在神经节内，细胞体根据神经分支位置呈现出松散的躯体定位：躯干电感受器的细胞体位于神经节尾部；头部感受器的细胞体位于神经节头部。头部的细胞体呈现出大致的背腹极性，眶上细胞倾向于位于背侧，眶下细胞位于中央，下颌细胞位于腹侧。尽管存在这种总体的躯体定位，但各区域之间的细胞体有大量重叠（高达30%）。神经分支区域内似乎不存在头尾拓扑结构。将离子电渗法注入ELL内侧段的WGA-HRP逆行标记了支配壶腹器官的细胞体。这些细胞体分散在整个神经节中，表明细胞体不会按受体类型聚集。从神经节向外周延伸的轴突似乎经历了积极的重组以形成神经分支。在神经分支内，通向皮肤特定区域的轴突不会聚集在一起。从神经节向中枢延伸时，轴突保持其细胞体的位置，直到到达ELL边界。一旦进入ELL，纤维会根据受体类型和它们终止的图谱在深层纤维层中进行分类。这种重组涉及束状结构和束状结构内轴突的重新排列。总体而言，从外周向中枢推进，电感应外周在远端神经和神经节中至少失去了其受体拓扑结构的一部分，然后在到达ELL后获得了功能和躯体定位组织；从概念上讲，它被拆除并重新构建。从个体发育的角度来看，轴突生长从神经节向外进行；神经节细胞体没有高度组织化，而它们支配的感受器及其中枢突却高度组织化，这一事实表明涉及主动的轴突导向机制。
