Effect of nonlinear summation of synaptic currents on the input-output properties of spinal motoneurons
Effect of nonlinear summation of synaptic currents on the input-output properties of spinal motoneurons
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DOI：
10.1152/jn.00439.2005
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发表时间：
2005-11-01
影响因子：
2.5
通讯作者：
Rose, PK
中科院分区：
文献类型：
--
作者：
Cushing, S;Bui, T;Rose, PK
单个脊髓运动神经元接收成千上万的突触。许多突触释放的神经递质作用于亲离子受体，改变邻近突触的驱动电位。这种相互作用在运动神经元输入-输出特性中引入了内在的非线性，其中对两个同时输入的响应小于对每个单独输入的响应的线性和。我们的目标是确定这种非线性的影响，在激活预定数量和分布的兴奋性和抑制性突触的过程中，传递到索马的电流。为了实现这一目标，我们构建了三个猫运动神经元的树突树的几何形状的详细测量约束的房室模型。由于驱动电位的局部变化而导致的电流“损失”是相当大的，并导致活动突触的数量与到达索马的电流之间的高度非线性关系。由兴奋性和抑制性突触的平衡激活组成的背景突触活动进一步降低了传递到索马的电流，但降低了相对于活跃兴奋性突触总数的非线性。出乎意料的是，模拟实验测量的非线性求和，激活两组兴奋性突触，导致接近线性求和。这个结果表明，非线性求和可能难以检测，尽管从非线性求和产生的电流的实质性“损失”。这种“损失”的程度似乎限制了运动神经元的活动，仅基于离子型受体的激活，水平不足以产生功能上有意义的肌肉力量。
A single spinal motoneuron receives tens of thousands of synapses. The neurotransmitters released by many of these synapses act on iontotropic receptors and alter the driving potential of neighboring synapses. This interaction introduces an intrinsic nonlinearity in motoneuron input-output properties where the response to two simultaneous inputs is less than the linear sum of the responses to each input alone. Our goal was to determine the impact of this nonlinearity on the current delivered to the soma during activation of predetermined numbers and distributions of excitatory and inhibitory synapses. To accomplish this goal we constructed compartmental models constrained by detailed measurements of the geometry of the dendritic trees of three feline motoneurons. The current "lost" as a result of local changes in driving potential was substantial and resulted in a highly nonlinear relationship between the number of active synapses and the current reaching the soma. Background synaptic activity consisting of a balanced activation of excitatory and inhibitory synapses further decreased the current delivered to the soma, but reduced the nonlinearity with respect to the total number of active excitatory synapses. Unexpectedly, simulations that mimicked experimental measures of nonlinear summation, activation of two sets of excitatory synapses, resulted in nearly linear summation. This result suggests that nonlinear summation can be difficult to detect, despite the substantial "loss" of current arising from nonlinear summation. The magnitude of this "loss" appears to limit motoneuron activity, based solely on activation of iontotropic receptors, to levels that are inadequate to generate functionally meaningful muscle forces.