Dicke U, Roth G, Matsushima T
Brain Research Institute, University of Bremen, Germany.
Acta Anat (Basel). 1998;163(3):127-43. doi: 10.1159/000046492.
Descending pathways to premotor/motor centers and their cell groups of origin were studied by means of retrograde biocytin tracing experiments in the frog Discoglossus pictus and the plethodontid salamander Plethodon jordani, which differ remarkably in the structure and function of their feeding apparatus and their feeding strategy. Labeled neurons were found in 30 major cell groups located in the telencephalon, diencephalon, synencephalon, mesencephalon and rhombencephalon. The number and distribution of nuclei are very similar in both species. Furthermore, the descending pathways of these groups of neurons take the same courses inside the medulla oblongata. Axons of most nuclei descend either in the ventromedial or ventrolateral medulla oblongata, and it is concluded that the spatial arrangement of pathways is identical in the species studied. Bilateral electrical stimulation of the optic tectum of the plethodontid salamander Hydromantes italicus elicited strong discharges of short latencies in the hypoglossal nerve. In most hypoglossal motor neurons, excitatory postsynaptic potentials (EPSPs) of short latencies followed paired shocks applied at intervals as short as 3 ms, but showed temporal and spatial facilitation, suggesting that the EPSPs include mono- as well as polysynaptic components. In the ventral white matter, orthodromic single units were found that are candidates for excitatory reticular interneurons. These properties of tectal descending pathways in salamanders strongly differ from those found in toads. Differences in feeding behavior and its control by the premotor/motor networks between the species investigated do not appear to result from anatomically altered input or from a different organization of descending pathways to these premotor/motor centers, but rather from differences in local properties of reticular premotor networks as well as from different effects of neuromodulatory systems.
通过逆行生物胞素追踪实验，对盘舌蟾和红背无肺螈这两种在摄食器官结构与功能以及摄食策略上存在显著差异的蛙类和螈类动物，研究了其至运动前区/运动中枢及其起源细胞群的下行通路。在位于端脑、间脑、联合脑、中脑和后脑的30个主要细胞群中发现了标记神经元。两种物种中核的数量和分布非常相似。此外，这些神经元群的下行通路在延髓内走行相同。大多数核的轴突在延髓腹内侧或腹外侧下行，得出在所研究的物种中通路的空间排列是相同的结论。对意大利水螈的视顶盖进行双侧电刺激，可在舌下神经中引发短潜伏期的强放电。在大多数舌下运动神经元中，短潜伏期的兴奋性突触后电位（EPSP）在短至3毫秒的间隔施加成对刺激后出现，但表现出时间和空间易化，表明EPSP包括单突触和多突触成分。在腹侧白质中，发现了正向单单位，它们是兴奋性网状中间神经元的候选者。螈类动物顶盖下行通路的这些特性与蟾蜍中的特性有很大不同。所研究物种之间在摄食行为及其由运动前区/运动网络控制方面的差异，似乎不是由于解剖学上改变的输入或至这些运动前区/运动中枢的下行通路的不同组织，而是由于网状运动前网络的局部特性差异以及神经调节系统的不同作用。
