Elekes K, Szabo T
Neuroscience. 1985 Jun;15(2):431-43. doi: 10.1016/0306-4522(85)90224-6.
The ultrastructure and synaptic organization of the presumed medullary pacemaker nucleus, nucleus c of the weakly electric mormyrid fish, Gnathonemus petersii has been investigated. Nucleus c consists of about 12-15 small (20-25 micron) neurones (P-cells), which form a group situated ventrally to the medullary relay nucleus and embedded in a neuropil of myelinated fibres and dendritic processes. The P-cells often exhibit an enhanced electron density of their cytoplasm and dendroplasm. They possess several dendrites of different diameter, a short, thin axon initial segment and a thickly myelinated axon running in dorsal direction. The pacemaker neurons are interconnected by complex electronic coupling, established by somatosomatic, dendrosomatic and dendrodendritic gap junctions. Perikarya and dendrites are frequently interconnected serially by gap junctions; dendrites showed sometimes triadic gap-junction arrangement. It is suggested that this high degree of electrotonic coupling amongst the pacemaker cells represents the first level of the highly ordered synchronization processes which characterize the electric discharge command system of Gnathonemus. Pacemaker cells receive synaptic input from club endings with mixed synapses and from bouton-like terminals with chemical synapses, both of them originating from medium-sized myelinated fibres and contacting mainly neuronal perikarya and dendritic processes. The axon initial segment receives only few synaptic inputs. Bouton-like terminals were found to be of two types according to their vesicle content, namely, boutons with ovoid, clear synaptic vesicles forming Gray type-1 synapses and boutons with pleomorphic clear synaptic vesicles forming Gray type-2 synapses. Different functional roles for the two types of boutons in modulating pacemaker cell activity are suggested.
对弱电鱼裸臀鱼假定的延髓起搏器核（c核）的超微结构和突触组织进行了研究。c核由大约12 - 15个小（20 - 25微米）神经元（P细胞）组成，这些神经元形成一个位于延髓中继核腹侧的群体，并嵌入有髓纤维和树突状突起的神经毡中。P细胞的细胞质和树突质通常表现出增强的电子密度。它们有几个不同直径的树突、一个短而细的轴突起始段和一个向背侧延伸的厚髓鞘轴突。起搏器神经元通过复杂的电耦合相互连接，这种电耦合由体细胞 - 体细胞、树突 - 体细胞和树突 - 树突缝隙连接建立。胞体和树突经常通过缝隙连接连续相互连接；树突有时呈现三联体缝隙连接排列。有人认为，起搏器细胞之间这种高度的电紧张耦合代表了高度有序同步过程的第一级，这种同步过程是裸臀鱼放电指令系统的特征。起搏器细胞从具有混合突触的棒状终末和具有化学突触的纽扣状终末接收突触输入，这两种终末均源自中等大小的有髓纤维，主要与神经元胞体和树突状突起接触。轴突起始段仅接收少量突触输入。根据其囊泡内容物，纽扣状终末被发现有两种类型，即具有卵形、清亮突触囊泡形成Gray I型突触的终末和具有多形清亮突触囊泡形成Gray II型突触的终末。有人提出这两种类型的终末在调节起搏器细胞活动中具有不同的功能作用。
