O'Donovan M J, Chub N, Wenner P
Section of Developmental Neurobiology, Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Neurobiol. 1998 Oct;37(1):131-45. doi: 10.1002/(sici)1097-4695(199810)37:1<131::aid-neu10>3.0.co;2-h.
Developing networks of the chick spinal cord become spontaneously active early in development and remain so until hatching. Experiments using an isolated preparation of the spinal cord have begun to reveal the mechanisms responsible for this activity. Whole-cell and optical recordings have shown that spinal neurons receive a rhythmic, depolarizing synaptic drive and experience rhythmic elevations of intracellular calcium during spontaneous episodes. Activity is expressed throughout the neuraxis and can be produced by different parts of the cord and by the isolated brain stem, suggesting that it does not depend upon the details of network architecture. Two factors appear to be particularly important for the production of endogenous activity. The first is the predominantly excitatory nature of developing synaptic connections, and the second is the presence of prolonged activity-dependent depression of network excitability. The interaction between high excitability and depression results in an equilibrium in which episodes are expressed periodically by the network. The mechanism of the rhythmic bursting within an episode is not understood, but it may be due to a "fast" form of network depression. Spontaneous embryonic activity has been shown to play a role in neuron and muscle development, but is probably not involved in the initial formation of connections between spinal neurons. It may be important in refining the initial connections, but this possibility remains to be explored.
鸡胚脊髓神经网络在发育早期就开始自发活动，并一直持续到孵化。使用脊髓离体标本进行的实验已开始揭示这种活动的产生机制。全细胞记录和光学记录表明，脊髓神经元在自发活动期间会接收到节律性的去极化突触驱动，并经历细胞内钙的节律性升高。这种活动在整个神经轴中都有表现，并且可以由脊髓的不同部位以及离体脑干产生，这表明它不依赖于网络结构的细节。对于内源性活动的产生，有两个因素似乎尤为重要。第一个因素是发育中的突触连接主要具有兴奋性，第二个因素是存在长时间的依赖活动的网络兴奋性抑制。高兴奋性和抑制之间的相互作用导致一种平衡状态，在这种状态下，网络会周期性地表现出活动。一次活动中节律性爆发的机制尚不清楚，但可能是由于一种“快速”形式的网络抑制。自发的胚胎活动已被证明在神经元和肌肉发育中起作用，但可能不参与脊髓神经元之间连接的初始形成。它可能在优化初始连接方面很重要，但这一可能性仍有待探索。
