VOLTAGE-CLAMP AND SPACE-CLAMP ERRORS ASSOCIATED WITH THE MEASUREMENT OF ELECTROTONICALLY REMOTE SYNAPTIC EVENTS
VOLTAGE-CLAMP AND SPACE-CLAMP ERRORS ASSOCIATED WITH THE MEASUREMENT OF ELECTROTONICALLY REMOTE SYNAPTIC EVENTS
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DOI：
10.1152/jn.1993.70.2.781
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发表时间：
1993-08-01
影响因子：
2.5
通讯作者：
JOHNSTON, D
中科院分区：
文献类型：
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作者：
SPRUSTON, N;JAFFE, DB;JOHNSTON, D
1.使用等效圆柱模型和形态学上真实的神经元树突树模型来评估与使用体细胞电极来测量来自树突突触的电流相关联的电压钳和空间钳误差。作为了解电压钳条件下突触电流失真的特性的第一步，在等效圆柱模型中评估阶跃和正弦电压变化的衰减。电缆中的电压的频率依赖性衰减的演示然后被用作理解在远离体细胞记录电极的位点处产生的突触电流的失真的框架，并且在电压钳记录配置中测量。比膜电阻率（R（m））的增加，以减少稳态电压衰减，而产生的瞬态电压变化的衰减只有最小的减少。因此，增加R（m）的实验操作提高了对电紧张性远程突触的反转电位的估计的准确性，但不会显著降低峰值电流的衰减。此外，R（m）的增加具有减慢不良钳位突触电流的动力学的作用。突触电导的大小及其动力学上测得的突触电流的影响也检查和讨论。从测量的突触电流估计参数的误差是最大的突触与快速动力学和大电导。CA 3锥体神经元的形态逼真的模型被用来证明从等效圆柱模型得出的结论的一般性。现实的模型也被用来拟合突触电流产生的苔藓纤维（MF）和连合/联合（C/A）输入到CA 3神经元的刺激，并估计这些测量电流的失真量。从CA 3锥体神经元模型的解剖数据被用来构建一个简化的双圆柱CA 3模型。该模型用于估计MF突触（位于索马近端）和穿通通路（PP）突触（位于顶树突远端）的电紧张距离以及这些突触的测量的突触电流参数的失真。结果从等效圆柱模型，形态CA 3模型，和简化的CA 3模型都表明，突触电流的失真量急剧增加的函数从索马的距离。靠近索马的MF突触可能只受到小的空间钳误差，而远离索马的MF突触可能被显著衰减。来自更远的突触，如C/A和PP输入的突触电流被证明是极大地衰减。总之，我们表明，尽管实验操作，以消除体细胞泄漏电导和增加R（m），突触电流产生的神经元树突和测量的索马仍然可以显着衰减和扭曲。因此，在索马进行的电压钳测量对突触电导和动力学的估计应该与这些测量相关的误差估计配对。这样的估计将需要对所研究的突触的位置和动力学以及突触后神经元的电紧张结构的了解。远程突触事件的非箝位性质也提高了树突中的电压门控通道可能被突触输入激活的可能性，即使在电压箝位条件下。
1. The voltage- and space-clamp errors associated with the use of a somatic electrode to measure current from dendritic synapses are evaluated using both equivalent-cylinder and morphologically realistic models of neuronal dendritic trees.2. As a first step toward understanding the properties of synaptic current distortion under voltage-clamp conditions, the attenuation of step and sinusoidal voltage changes are evaluated in equivalent cylinder models. Demonstration of the frequency-dependent attenuation of voltage in the cable is then used as a framework for understanding the distortion of synaptic currents generated at sites remote from the somatic recording electrode and measured in the voltage-clamp recording configuration.3. Increases in specific membrane resistivity (R(m)) are shown to reduce steady-state voltage attenuation, while producing only minimal reduction in attenuation of transient voltage changes. Experimental manipulations that increase R(m) therefore improve the accuracy of estimates of reversal potential for electrotonically remote synapses, but do not significantly reduce the attenuation of peak current. In addition, increases in R(m) have the effect of slowing the kinetics of poorly clamped synaptic currents.4. The effects of the magnitude of the synaptic conductance and its kinetics on the measured synaptic currents are also examined and discussed. The error in estimating parameters from measured synaptic currents is greatest for synapses with fast kinetics and large conductances.5. A morphologically realistic model of a CA3 pyramidal neuron is used to demonstrate the generality of the conclusions derived from equivalent cylinder models. The realistic model is also used to fit synaptic currents generated by stimulation of mossy fiber (MF) and commissural/associational (C/A) inputs to CA3 neurons and to estimate the amount of distortion of these measured currents.6. Anatomic data from the CA3 pyramidal neuron model are used to construct a simplified two-cylinder CA3 model. This model is used to estimate the electrotonic distances of MF synapses (which are located proximal to the soma) and perforant path (PP) synapses (which are located at the distal ends of the apical dendrites) and the distortion of synaptic current parameters measured or these synapses.7. Results from the equivalent-cylinder models, the morphological CA3 model, and the simplified CA3 model all indicate that the amount of distortion of synaptic currents increases steeply as a function of distance from the soma. MF synapses close to the soma are likely to be subject only to small space-clamp errors, whereas MF synapses farther from the soma are likely to be substantially attenuated. Synaptic currents from more remote synapses such as C/A and PP inputs are shown to be enormously attenuated.8. In conclusion, we show that despite experimental manipulations to eliminate somatic leak conductances and increase R(m), synaptic currents generated in neuronal dendrites and measured at the soma can still be significantly attenuated and distorted. Estimates of synaptic conductances and kinetics from voltage-clamp measurements made at the soma should therefore be paired with estimates of the errors associated with these measurements. Such estimates will require a knowledge of the location and kinetics for the synapse under study as well as the electrotonic structure of the postsynaptic neuron. The unclamped nature of remote synaptic events also raises the possibility that voltage-gated channels in dendrites may be activated by synaptic inputs, even under voltage-clamp conditions.