Modulation of leg motoneuron activity in the stick insect: The importance of acetylcholine and octopamine and the role of subesophageal descending neurons

竹节虫腿部运动神经元活动的调节：乙酰胆碱和章鱼胺的重要性以及食管下下降神经元的作用

• 批准号: 263884427
• 负责人: Privatdozent Dr. Joachim Schmidt
• 金额: --
• 依托单位: Institut für Zoologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2014
• 资助国家: 德国
• 起止时间: 2013-12-31 至 2017-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/263884427?language=en
• 关键词: Modulation; leg; motoneuron; activity; stick

The contractions of the leg musculature in a walking animal are controlled by motoneurons. The activity of these motoneurons is determined by tonic depolarizing drive, phasic structuring input from leg sense organs and neurons in the CNS and by neuro-modulatory influences. In the stick insect, we wish to elucidate the mechanisms of the tonic excitation and the role of subesophageal neurons in the modulation of motoneuron activity.Application of the muscarinic acetylcholine agonist pilocarpine to the thoracic ganglia of the stick insect evokes a tonic excitation in motoneurons and activates oscillatory neural networks (CPGs). Inhibition by CPGs structures motoneuron activity. However, the exact place of the receptors where acetylcholine acts when it evokes the tonic excitation is not known. We wish to find out whether the tonic excitation is mediated by muscarinc receptors located on motoneurons or on premotor neurons. We know that the tonic excitation is modulated by the biogenic amine octopamine. The localization of the muscarinic receptors will help in unrevealing the mechanisms of the octopaminergic modulation.Octopamine, which is seen as the invertebrate counterpart of adrenalin, modulates a plethora of different functions in insects. For example, it modulates walking and flying behavior and the activity of muscles and sense organs. In stick insects octopamine blocks an inward current induced by activation of a nicotinc acetycholine receptor. However, so far it is not known which octopaminergic neurons modulate the activity of neurons in the thoracic ganglia in insects. Therefore, in the second part of our project we wish to explore in stick insects the modulation leg motoneuron activity by descending neurons in the subesophageal ganglion. These 5-6 unpaired neurons (DUM neurons, dorsal unpaired median) have been identified as octopaminergic cells in some orthopteran insects. The axons of these cells descend through both thoracic connectives their function is not known. Only recently, in some pilot experiments we could show that some of these neurons modulate sensory-motor interaction. Specifically, the activation of a single DUM neuron partially blocks the activity in an extensor tibiae motoneuron that is evoked by stimulation of a sense organ that mimics flexion of the respective joint. We attempt to substantiate this finding and investigate the mechanisms of this modulation. A block of cholingeric signal transmission is possible as sensory neurons utilize acetylcholine as a transmitter. We also attempt to test whether the modulation depends on the behavioral state of the animal, i.e. resting animal vs. walking animal. In addition, we would like to find out whether effects by other sense organs and the tonic excitation are also modulated.

行走动物腿部肌肉的收缩是由运动神经元控制的。这些运动神经元的活动是由紧张性去极化驱动、腿部感觉器官和中枢神经系统神经元的时相结构输入以及神经调节影响决定的。在棒状昆虫中，我们希望阐明紧张性兴奋的机制和食道下神经元在运动神经元活动调节中的作用。在棒状昆虫的胸神经节上应用毒扁豆碱乙酰胆碱激动剂匹罗卡品可以引起运动神经元的紧张性兴奋，并激活振荡神经网络(CPGs)。CPGs的抑制作用构成运动神经元活性。然而，当乙酰胆碱引起紧张性兴奋时，受体的确切作用位置尚不清楚。我们希望弄清楚这种紧张性兴奋是由运动神经元上的M受体还是运动前神经元上的M受体介导的。我们知道紧张性兴奋是由生物胺章鱼胺调制的。M受体的定位将有助于揭示章鱼胺能调节的机制。章鱼胺被视为肾上腺素的无脊椎动物对应物，在昆虫中调节大量不同的功能。例如，它调节行走和飞行行为以及肌肉和感觉器官的活动。在棍虫体内，章鱼能阻断一种由烟碱乙酰胆碱受体激活而产生的内向电流。然而，到目前为止，还不知道昆虫胸神经节中哪些八胺能神经元调节神经元的活动。因此，在我们项目的第二部分，我们希望探索棒虫通过食道下神经节中的下行神经元来调节腿运动神经元的活动。这些5-6个不成对的神经元(DUM神经元，背侧不成对的正中神经元)在一些直翅目昆虫中被鉴定为八胺能细胞。这些细胞的轴突通过两个胸椎结缔组织下行，其功能尚不清楚。直到最近，在一些先导性实验中，我们才能证明其中一些神经元调节感觉-运动相互作用。具体地说，单个DUM神经元的激活部分阻断了胫骨伸肌运动神经元的活动，该活动是由刺激模拟各自关节屈曲的感觉器官而引起的。我们试图证实这一发现，并研究这种调节的机制。当感觉神经元利用乙酰胆碱作为递质时，胆碱能信号的传递是可能的。我们还试图测试这种调节是否取决于动物的行为状态，即休息动物与行走动物。此外，我们还想知道其他感觉器官的影响和紧张性兴奋是否也受到调制。