AMPLIFICATION AND LINEARIZATION OF DISTAL SYNAPTIC INPUT TO CORTICAL PYRAMIDAL CELLS
AMPLIFICATION AND LINEARIZATION OF DISTAL SYNAPTIC INPUT TO CORTICAL PYRAMIDAL CELLS
复制标题
DOI：
10.1152/jn.1994.72.6.2743
复制
发表时间：
1994-12-01
影响因子：
2.5
通讯作者：
DOUGLAS, RJ
中科院分区：
文献类型：
--
作者：
BERNANDER, O;KOCH, C;DOUGLAS, RJ
1. 采用计算机模拟的方法，研究了锥体细胞顶端树突树钙钾电导电压依赖性对顶端突触输入突触效能的影响。第1层和第2层的顶端丛是其他皮质区域反馈投射的目标。电流，I-soma，流入soma响应突触输入被用来评估突触的功效。这一措施充分考虑了树突中所有相关的非线性，可以在尖峰活动期间使用。I-soma强调响应突触输入的电流流动，而不是突触诱导的电压变化。通过计算突触前输入和突触后输出频率之间的关系，该方法还允许明确表征整个神经元的输入-输出关系。仿真基于两个模型。第一个是成年猫纹状皮层第5层锥体细胞的生物物理详细400室模型。在这个模型中，八个电压相关的电导被纳入体细胞膜，以提供观察到的正常尖峰细胞的放电行为。第二个模型是一个高度简化的三室等效电路。如果树突完全是被动的，非n-甲基- d -天冬氨酸（non-NMDA）类型的兴奋性突触输入到第1层、第2层和第3层以非常适中的输入速率饱和，因为顶端丛的输入阻抗很高。第1层和第2层一起只能向体细胞提供0.25 nA电流。考虑到重要的传入事件在顶丛上发生突触，这种适度的影响是令人惊讶的，并且与表明更强大影响的实验数据不一致。我们以一种可控的方式在根尖簇中引入电压依赖的钾电导g(K)，以防止突触反应饱和。这个电导被设计成线性化突触前输入频率和体细胞电流之间的关系。我们还引入了沿根尖主干的电压依赖性钙电导g（Ca）来放大根尖信号，即到达体细胞的突触电流。为了得到突触前输入速率与突触输入传递的体细胞电流之间的具体关系，我们用解析法或数值法推导了g(K)和g（Ca）的激活曲线。由此产生的两种电导的电压依赖性行为与实验测量的激活曲线相似。我们认为根尖丛代表了一个单独的整合区域，它通过根尖树突中的电流放大器与体细胞耦合。放大器的增益可以通过调制g（Ca）或g(K)的特性来控制。
1. Computer simulations were used to study the effect of voltage-dependent calcium and potassium conductances in the apical dendritic tree of a pyramidal cell on the synaptic efficacy of apical synaptic input. The apical tuft in layers 1 and 2 is the target of feedback projections from other cortical areas.2. The current, I-soma, flowing into the soma in response to synaptic input was used to assess synaptic efficacy. This measure takes full account of all the relevant nonlinearities in the dendrites and can be used during spiking activity. I-soma emphasizes current flowing in response to synaptic input rather than synaptically induced voltage change. This measure also permits explicit characterization of the input-output relationship of the entire neuron by computing the relationship between presynaptic input and postsynaptic output frequency.3. Simulations were based on two models. The first was a biophysically detailed 400-compartment model of a morphologically characterized layer 5 pyramidal cell from striate cortex of an adult cat. In this model eight voltage-dependent conductances were incorporated into the somatic membrane to provide the observed firing behavior of a regular spiking cell. The second model was a highly simplified three-compartment equivalent electrical circuit.4. If the dendritic tree is entirely passive, excitatory synaptic input of the non-N-methyl-D-aspartate (non-NMDA) type to layers 1, 2, and 3 saturate at very moderate input rates, because of the high input impedance of the apical tuft. Layers 1 and 2 together can deliver only 0.25 nA current to the soma. This modest effect is surprising in view of the important afferents that synapse on the apical tuft and is inconsistent with experimental data indicating a more powerful effect.5. We introduced in a controlled manner a voltage-dependent potassium conductance in the apical tuft, g(K), to prevent saturation of the synaptic response. This conductance was designed to linearize the relationship between presynaptic input frequency and the somatic current. We also introduced a voltage-dependent calcium conductance along the apical trunk, g(Ca) to amplify the apical signal, i.e., the synaptic current reaching the soma.6. To arrive at a specific relationship between the presynaptic input rate and the somatic current delivered by the synaptic input, we derived the activation curves of g(K) and g(Ca) either analytically or numerically. The resultant voltage-dependent behavior of both conductances was similar to experimentally measured activation curves.7. We propose that the apical tuft represents a separate integrative region that is coupled to the soma by a current amplifier in the apical dendrite. The gain of the amplifier can be controlled by modulating the properties of either g(Ca) or g(K).