Elekes K, Szabo T
Exp Brain Res. 1985;60(3):509-20. doi: 10.1007/BF00236936.
The general organization and synaptology of the medullary command (pacemaker) nucleus (MCN) was investigated in the high frequency weakly electric fish, Apteronotus leptorhynchus. This study was undertaken in order to establish differences and similarities between the MCN of A. leptorhynchus and that of the closely related species, Apteronotus albifrons which has been studied previously. The basic morphology and synaptology of the MCN in A. leptorhynchus is similar to that of A. albifrons. The MCN of A. leptorhynchus consists of large (relay) and small (pacemaker) cells; both cell types receive synaptic input or large club endings with electrotonic gap junctions and bouton-like terminals with polarized chemical synapses. Club endings originate from thick meyelinated fibres belonging to the small (pacemaker) cells, whereas the bouton-like terminals issue from thin myelinated fibers of extranuclear origin. Via their club endings, the small (pacemaker) cells are connected both to each other and to the large (relay) cells. Besides the similarities, there are distinct and characteristic differences between the MCN of the two species, which mainly concern the synaptology of the nucleus. In A. leptorhynchus, the large (relay) cells possess long dendritic processes, covered exclusively with bouton-like terminals; the axon initial segment of large (relay) cells receives boutons, in addition to club endings. Small (pacemaker) cells have short dendritic protrusions receiving input from club endings and boutons; furthermore, the small pacemaker cells axon initial segment receives both club endings and bouton-like terminals. These differences are discussed in terms of the functional organization of the MCN in certain gymnotoids and draw attention to the fact that the morphological and ultrastructural aspects of the central command of the electric organ discharge reveal several differences not only between different gymnotoid fish (Apteronotus and Eigenmannia) but also between closely related species such as A. albifrons and A. leptorhynchus.
在高频弱电鱼线翎电鳗中，对延髓指令（起搏器）核（MCN）的总体组织结构和突触学进行了研究。开展这项研究是为了确定线翎电鳗的MCN与先前已研究过的近缘物种艾氏电鳗的MCN之间的异同。线翎电鳗MCN的基本形态和突触学与艾氏电鳗相似。线翎电鳗的MCN由大（中继）细胞和小（起搏器）细胞组成；这两种细胞类型都接收突触输入，大的棒状终末带有电紧张性缝隙连接，以及带有极化化学突触的纽扣状终末。棒状终末起源于属于小（起搏器）细胞的粗有髓纤维，而纽扣状终末则来自核外起源的细有髓纤维。小（起搏器）细胞通过其棒状终末彼此相连，并与大（中继）细胞相连。除了相似之处外，这两个物种的MCN之间还存在明显的特征差异，主要涉及该核的突触学。在线翎电鳗中，大（中继）细胞具有长树突突起，仅覆盖有纽扣状终末；大（中继）细胞的轴突起始段除了接收棒状终末外，还接收纽扣。小（起搏器）细胞具有短的树突突起，接收来自棒状终末和纽扣的输入；此外，小起搏器细胞的轴突起始段接收棒状终末和纽扣状终末。根据某些裸背电鳗类动物中MCN的功能组织对这些差异进行了讨论，并提请注意这样一个事实，即电器官放电的中枢指令的形态和超微结构方面不仅在不同的裸背电鳗类鱼（线翎电鳗属和真电鳗属）之间，而且在艾氏电鳗和线翎电鳗等近缘物种之间都显示出一些差异。
