Grigonis Ramunas, Alaburda Aidas
Department of Neurobiology and Biophysics, Institute of Biosciences, Vilnius University, Sauletekio ave. 7, LT-10257, Vilnius, Lithuania.
J Physiol. 2017 Sep 1;595(17):5843-5855. doi: 10.1113/JP274434. Epub 2017 Jul 26.
Action potential threshold can vary depending on firing history and synaptic inputs. We used an ex vivo carapace-spinal cord preparation from adult turtles to study spike threshold dynamics in motoneurons during two distinct types of functional motor behaviour - fictive scratching and fictive swimming. The threshold potential depolarizes by about 10 mV within each burst of spikes generated during scratch and swim network activity and recovers between bursts to a slightly depolarized level. Slow synaptic integration resulting in a wave of membrane potential depolarization is the factor influencing the threshold potential within firing bursts during motor behaviours. Depolarization of the threshold potential decreases the excitability of motoneurons and may provide a mechanism for stabilization of the response of a motoneuron to intense synaptic inputs to maintain the motor commands within an optimal range for muscle activation.
During functional spinal neural network activity motoneurons receive intense synaptic input, and this could modulate the threshold for action potential generation, providing the ability to dynamically adjust the excitability and recruitment order for functional needs. In the present study we investigated the dynamics of action potential threshold during motor network activity. Intracellular recordings from spinal motoneurons in an ex vivo carapace-spinal cord preparation from adult turtles were performed during two distinct types of motor behaviour - fictive scratching and fictive swimming. We found that the threshold of the first spike in episodes of scratching and swimming was the lowest. The threshold potential depolarizes by about 10 mV within each burst of spikes generated during scratch and swim network activity and recovers between bursts to a slightly depolarized level. Depolarization of the threshold potential results in decreased excitability of motoneurons. Synaptic inputs do not modulate the threshold of the first action potential during episodes of scratching or of swimming. There is no correlation between changes in spike threshold and interspike intervals within bursts. Slow synaptic integration that results in a wave of membrane potential depolarization rather than fast synaptic events preceding each spike is the factor influencing the threshold potential within firing bursts during motor behaviours.
动作电位阈值可因发放历史和突触输入而变化。我们使用成年海龟的离体甲壳-脊髓标本，研究在两种不同类型的功能性运动行为——虚构抓挠和虚构游泳过程中运动神经元的动作电位阈值动态变化。在抓挠和游泳网络活动期间产生的每个动作电位爆发中，阈值电位去极化约10 mV，并在爆发之间恢复到略去极化水平。导致膜电位去极化波的缓慢突触整合是影响运动行为期间发放爆发中阈值电位的因素。阈值电位的去极化降低了运动神经元的兴奋性，并可能提供一种机制，使运动神经元对强烈突触输入的反应稳定，从而将运动指令维持在肌肉激活的最佳范围内。
在功能性脊髓神经网络活动期间，运动神经元会接收到强烈的突触输入，这可能会调节动作电位产生的阈值，从而能够根据功能需求动态调整兴奋性和募集顺序。在本研究中，我们研究了运动网络活动期间动作电位阈值的动态变化。在成年海龟的离体甲壳-脊髓标本中，对脊髓运动神经元进行细胞内记录，记录过程中出现两种不同类型的运动行为——虚构抓挠和虚构游泳。我们发现，抓挠和游泳发作中第一个动作电位的阈值最低。在抓挠和游泳网络活动期间产生的每个动作电位爆发中，阈值电位去极化约10 mV，并在爆发之间恢复到略去极化水平。阈值电位的去极化导致运动神经元兴奋性降低。突触输入在抓挠或游泳发作期间不会调节第一个动作电位的阈值。爆发内动作电位阈值变化与峰峰间期之间没有相关性。导致膜电位去极化波的缓慢突触整合而非每个动作电位之前的快速突触事件是影响运动行为期间发放爆发中阈值电位的因素。
