摘要
为了揭示神经网络在脊椎动物运动中所行使的内在功能,作者开发了七鳃鳗这种低等脊椎动物模型。在这套系统中,不仅可以了解到运动模式生成网络以及激活此网络的命令系统,同时还可以在运动中研究方向控制系统和变向控制系统。七鳃鳗的神经系统有较少的神经元,而且运动行为中的不同运动模式可以由分离的神经系统所引发。模式生成神经网络包括同侧的谷氨酸能中间神经元和对侧的抑制性甘氨酸能中间神经元。网络中的突触连接、细胞膜特性和神经递质都也已经被鉴定。运动是由脑干区域的网状脊髓神经元所引起,而这些神经元又是被间脑和中脑分离的一些运动命令神经元群所控制。因此,运动行为最初是由这两个"运动核心"所启动。而这两个运动核心被基底神经节调控,基底神经节即时地做出判断是否允许下游的运动程序启动。在静止情况下基底神经节的输出核团维持对下游不同运动核心的抑制作用,反之则去除抑制活化运动核心。纹状体和苍白球被认为是这个运动抉择系统的主要部件。根据"霍奇金-贺胥黎"模型神经元开发了这套网络模型,不同的细胞具有各自相应的不同亚型的钠、钾、钙离子通道和钙依赖的钾通道。每个模型神经元拥有86个不同区域模块以及其对应的生物学功能,例如频率控制、超极化等等。然后根据已有实验证据,利用突触将不同的模型神经元相连。而系统中的10000个神经元大致和生物学网络上的细胞数量相当。突触数量为760000。突触类型有AMPA、NMDA、glycine型。有了这样大规模的模型,不仅可以模拟肌节与肌节之间的神经网络,还可以模拟到由基底神经节开始的行为起始部分。此外,这些网络模拟还被用于一个神经机械学模型来模拟包含有推进和方向控制部分的真实运动。
To unravel the intrinsic function of the networks controlling vertebrate motor behaviour, we have developed a lower vertebrate model system, the lamprey. In this system it has been possible not only to unravel the intrinsic function of the pattern generating network and the command system by which it is activated, but also the control systems underlying steering and the control of body orientation during movements. The lamprey nervous system has fewer neurones, and the motor pattern underlying the locomotor behaviour can be elicited in the isolated nervous system. The pattern generating network contains ipsilateral glutamatergic interneurones and crossed inhibitory glycinergic interneurones. The synaptic interaction, membrane properties and transmitters in the network have been identified. It is activated from the brainstem reticulospinal neurones, which in turn are controlled from diencephalon and mesencephalon with separate populations of locomotor command neurones. The locomotor behaviour can thus be turned on from these two ＇locomotor centres＇. These two areas are in turn under the control from the basal ganglia, which play a main role for selection of which motor program is turned on at a given instant. The output nuclei of the basal ganglia provide tonic inhibition under resting conditions to different motor centres, and elicit activation of a centre through disinhibition. Striatum and pallidum are viewed as critical structures for the selection of a given motor program. We have developed detailed network models based on Hodgkin-Huxley model neurons of each cell type with appropriate sodium, potassium, calcium ion channel subtypes and also calcium dependent potassium channels. Each model neuron has up to 86 compartments and behaves as its biological counterpart, with regard to frequency regulation, afterhyperpolarization and so forth. The different network models neurons are then connected synaptically as established experimentally. The 10,000 model neurons correspond to the approximate number in the biological network. The number of synapses is 760,000. Synapses are of AMPA, NMDA and glycine type. With this large scale modelling, we can simulate not only the segmental and intersegmental coordination but also the initiation of behaviour from the basal ganglia. Moreover, these networks have also been used in a neuromechanical model simulating actual locomotion with propulsion and steering.
出处
《生命科学》
CSCD
2008年第5期695-701,共7页
Chinese Bulletin of Life Sciences
