Li Wen-Chang, Soffe Stephen R, Wolf Ervin, Roberts Alan
School of Biological Sciences, University of Bristol, Bristol BS8 1UG, United Kingdom.
J Neurosci. 2006 Apr 12;26(15):4026-35. doi: 10.1523/JNEUROSCI.4727-05.2006.
The ability of brief stimuli to trigger prolonged neuronal activity is a fundamental requirement in nervous systems, common to motor responses and short-term memory. Bistable membrane properties and network feedback excitation have both been proposed as suitable mechanisms to sustain such persistent responses. There is now good experimental evidence for membrane bistability. In contrast, the long-standing hypotheses based on positive feedback excitation have yet to be supported by direct evidence for mutual excitatory connections between appropriate neurons. In young frog tadpoles (Xenopus), we show that a small region of caudal hindbrain and rostral spinal cord is sufficient to generate prolonged swimming in response to a brief stimulus. We used paired whole-cell patch recordings to identify hindbrain neurons in this region that actively excite spinal neurons to drive sustained swimming. We show directly that some of these hindbrain neurons make reciprocal excitatory connections with each other. We use a population model of the hindbrain network to illustrate how feedback excitation can provide a robust mechanism to generate persistent responses. Our recordings provide direct evidence for feedback excitation among neurons within a network that drives a prolonged response. Its presence in a lower brain region early in development suggests that it is a basic feature of neuronal network design.
短暂刺激引发神经元活动延长的能力是神经系统的一项基本要求，在运动反应和短期记忆中都很常见。双稳态膜特性和网络反馈兴奋都被认为是维持这种持续反应的合适机制。目前已有关于膜双稳态的良好实验证据。相比之下，基于正反馈兴奋的长期假设尚未得到适当神经元之间相互兴奋性连接的直接证据支持。在幼体非洲爪蟾蝌蚪中，我们发现尾侧后脑和头侧脊髓的一个小区域足以在受到短暂刺激时产生延长的游泳行为。我们使用双电极全细胞贴片记录来识别该区域中能积极兴奋脊髓神经元以驱动持续游泳的后脑神经元。我们直接表明，其中一些后脑神经元相互之间形成了相互兴奋性连接。我们使用后脑网络的群体模型来说明反馈兴奋如何能够提供一种强大的机制来产生持续反应。我们的记录为驱动延长反应的网络内神经元之间的反馈兴奋提供了直接证据。它在发育早期出现在较低脑区，这表明它是神经元网络设计的一个基本特征。
