EFFECTIVE SYNAPTIC CURRENTS IN MOTONEURONS

在这个实验室进行的研究的长期目标是 了解哺乳动物运动神经元池的功能组织。 特别令人感兴趣的是突触输入的分布 节段性和下行性系统对运动神经元的作用及其在 形成脊髓的运动输出。 所采取的方法是 一个综合的，结合计算机建模和模拟研究， 猫脊髓运动神经元的电生理测量。 在这 更新申请，有三个具体目标。 第一特定 目的是继续研究如何有效的突触电流， 不同的输入系统被分配给 屈肌和伸肌运动神经元池。 一种改进的电压钳 在这些研究中将使用一种技术来测量电流的大小 它到达运动神经元的索马和起始段， 状态条件。 这个量被称为有效突触 电流（IN），因为只有那部分突触电流， 直接到达运动神经元的索马和起始段 影响了它的招募和发射频率 突触输入系统 将被研究的是一个低阈值，皮肤途径， 同侧屈肌反射传入（FRA）途径，皮质脊髓， 红核脊髓和外侧前庭脊髓通路。 第二 具体目的是研究不同的下行和节段性突触 系统在同时激活时相互作用。 的每一个中 实验中，一个下行系统（皮质脊髓，红核脊髓或 前庭脊髓的）将准备好与多达沿着的 五种不同的节段输入（Ia兴奋、Ia抑制、Renshaw 抑制、低阈值皮肤和FRA）。 将进行比较 每个输入端孤立产生的有效突触电流 当两个或多个输入时， 一起被激活。 此外，个人和 还将评估运动神经元放电速率的组合输入 在这些实验中，通过激活突触输入， 运动神经元对注入的电流脉冲作出反应 通过记录微电极。 第三个具体目标是测试 假设在稳态条件下， 由运动神经元到锋电位放电频率的突触输入可以 简单地描述为净有效突触电流的乘积 它们接收到的频率和它们的频率-电流关系的斜率， 射击的主要范围。 在这些实验中，频率电流 运动神经元的关系将被测量，以及有效的 由一个或多个输入产生的突触电流。 随后，委员会注意到， 相同的突触输入将被添加到注入的电流， 观察到的发射率变化将与基于 对有效突触电流的大小和斜率的影响 频率-电流关系

The long-term objective of the research conducted in this laboratory is to understand the functional organization of mammalian motoneuron pools. Of particular interest is the distribution of synaptic inputs from segmental and descending systems to motoneurons and their roles in shaping motor output from the spinal cord. The approach taken is a synthetic one, combining computer modelling and simulation studies with electrophysiological measurements in cat spinal motoneurons. In this renewal application, there are three specific aims. The first specific aim is to continue studies on how effective synaptic currents from different input systems are distributed to the constituent members of both flexor and extensor motoneuron pools. A modified, voltage clamp technique will be used in these studies to measure the amount of current that reaches the soma and initial segment of a motoneuron under steady- state conditions. This quantity is referred to as the effective synaptic current (IN) because only that fraction of a synaptic current that actually reaches the soma and initial segment of the motoneuron directly affects its recruitment and firing frequency. The synaptic input systems that will be studied are a low threshold, cutaneous pathway, an ipsilateral flexor reflex afferent (FRA) pathway, the corticospinal, the rubrospinal and the lateral vestibulospinal pathways. The second specific aim is to study how different descending and segmental synaptic systems interact when they are activated concurrently. In each of the experiments, one descending system (corticospinal, rubrospinal or vestibulospinal) will be prepared for stimulation along with as many as five different segmental inputs (Ia excitation, Ia inhibition, Renshaw inhibition, low-threshold cutaneous, and FRA). Comparisons will be made of the effective synaptic currents generated by each input in isolation with the net effective synaptic currents produced when two or more inputs are activated together. In addition, the effects of the individual and combined inputs on the rate of motoneuron discharge will also be assessed in these experiments by activating the synaptic inputs while the motoneurons are discharging in response to current pulses injected through the recording microelectrode. The third specific aim is to test the hypothesis that under steady-state conditions, the transformation of synaptic inputs by motoneurons into spike discharge frequency can be described simply as the product of the net effective synaptic current they receive and the slope of their frequency-current relations within the primary range of firing. In these experiments, the frequency-current relation of a motoneuron will be measured, as well as the effective synaptic currents generated in it by one or more inputs. Subsequently, the same synaptic inputs will be added to the injected currents and the observed change in firing rate will be compared to that predicted based on the magnitude of the effective synaptic current and the slope of the frequency-current relation.