Computer simulation of the responses of human motoneurons to composite 1A EPSPS: Effects of background firing rate
Computer simulation of the responses of human motoneurons to composite 1A EPSPS: Effects of background firing rate
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DOI：
10.1152/jn.1997.77.1.405
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发表时间：
1997-01-01
影响因子：
2.5
通讯作者：
Bawa, P
中科院分区：
文献类型：
--
作者：
Jones, KE;Bawa, P
建立了脊髓α运动神经元的两个隔室模型，以探讨背景放电率和对兴奋性输入的反应之间的关系。这些模拟的结果与以前从人类运动神经元获得的结果进行了比较，并与当前重复刺激人类运动神经元的模型进行了讨论。模型的形态和电缆参数是基于先前文献中报道的两种类型的猫运动神经元。每个模型包括五个电压依赖的通道，这些通道是用霍奇金-赫胥黎公式建模的。这些通道包括起始段的快Na+和K+通道，以及胞体隔室的快Na+和K+通道和慢K+通道。慢K+通道的密度和速率因子是不同的，直到模型能够重现猫中已识别类型的运动神经元的单峰AHP参数。兴奋性突触电导沿着等同的树突分布，密度与1a突触从肌梭到类型识别的猫运动神经元的密度相同。同时激活树突上的所有突触，可产生大的复合兴奋性突触后电位(EPSP)。短暂的去极化脉冲注入到等效树枝晶的一个隔室中，产生了类似于复合EPSPS的脉冲电位(PPS)。在节律放电过程中，观察复合EPSPS和PPS对两种运动神经元模型放电概率的影响。在刺激和模型运动神经元的棘波之间构建的刺激周时间直方图显示出兴奋性峰值，其积分时间过程与潜在的EPSP或PP的时间过程近似，如在猫运动神经元中所示。用反应概率量化了激发峰，并探讨了背景放电频率与反应概率的关系。就像在真实的人类运动神经元中一样，这些模型显示出反应概率和背景放电率之间的反向关系。反映反应概率和放电频率之间关系的生物物理特性包括不同放电频率下尖峰间期膜电压轨迹的形状和PP幅值的非线性变化。这些模拟结果表明，反应概率和背景放电率之间的关系是运动神经元的一个内在特征。基于猫运动神经元特性的模型的结果与人类运动神经元的结果相似，这表明人类运动神经元的节律性放电的生物物理特性与猫的相似。
Two compartmental models of spinal alpha motoneurons were constructed to explore the relationship between background firing rate and response to an excitatory input. The results of these simulations were compared with previous results obtained from human motoneurons and discussed in relation to the current model for repetitively firing human motoneurons. The morphologies and cable parameters of the models were based on two type-identified cat motoneurons previously reported in the literature. Each model included five voltage-dependent channels that were modeled using Hodgkin-Huxley formalism. These included fast Na+ and K+ channels in the initial segment and fast Na+ and K+ channels as well as a slow K+ channel in the soma compartment. The density and rate factors for the slow K+ channel were varied until the models could reproduce single spike AHP parameters for type-identified motoneurons in the cat. Excitatory synaptic conductances were distributed along the equivalent dendrites with the same density described for 1a synapses from muscle spindles to type-identified cat motoneurons. Simultaneous activation of all synapses on the dendrite resulted in a large compound excitatory postsynaptic potential (EPSP). Brief depolarizing pulses injected into a compartment of the equivalent dendrite resulted in pulse potentials (PPs), which resembled the compound EPSPs. The effects of compound EPSPs and PPs on firing probability of the two motoneuron models were examined during rhythmic firing. Peristimulus time histograms, constructed between the stimulus and the spikes of the model motoneuron, showed excitatory peaks whose integrated time course approximated the time course of the underlying EPSP or PP as has been shown in cat motoneurons. The excitatory peaks were quantified in terms of response probability, and the relationship between background firing rate and response probability was explored. As in real human motoneurons, the models exhibited an inverse relationship between response probability and background firing rate. The biophysical properties responsible for the relationship between response probability and firing rate included the shapes of the membrane voltage trajectories between spikes and nonlinear changes in PP amplitude during the interspike interval at different firing rates. The results from these simulations suggest that the relationship between response probability and background firing rate is an intrinsic feature of motoneurons. The similarity of the results from the models, which were based on the properties of cat motoneurons, and those from human motoneurons suggests that the biophysical properties governing rhythmic firing in human motoneurons are similar to those of the cat.