Koizumi Hidehiko, Smith Jeffrey C
Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Neurosci. 2008 Feb 13;28(7):1773-85. doi: 10.1523/JNEUROSCI.3916-07.2008.
A central problem in analyzing neural circuit function is establishing how intrinsic neuronal conductances contribute to the generation of network activity. We used real-time calcium activity imaging combined with whole-cell patch-clamp recording to analyze contributions of subthreshold conductances in the excitatory rhythm-generating network in the respiratory pre-Bötzinger complex (pre-BötC) of neonatal rat in vitro brainstem slice preparations. Voltage-clamp ramp recordings from imaged pre-BötC neurons revealed that persistent sodium (NaP) and K+-dominated leak currents primarily contribute to subthreshold I-V relations. We quantified NaP and leak conductance densities (g/C(m)) in intrinsic oscillatory bursters and intrinsically nonbursters, the two main electrophysiological phenotypes of inspiratory neurons within the pre-BötC. Densities of g(NaP) were significantly higher for intrinsic bursters, whereas leak conductance densities were not significantly different between intrinsic bursters and nonbursters. By pharmacologically manipulating g(NaP) and/or g(Leak) directly within the pre-BötC, we could modulate network oscillation frequency over a wide dynamic range and cause transitions between oscillatory and quiescent states. These results were consistent with models of the pre-BötC excitatory network consisting of heterogeneous mixtures of intrinsic bursters and nonintrinsic bursters incorporating g(NaP) and g(Leak) with parameter values found experimentally. We propose a paradigm whereby NaP and Leak represent a functional set of subthreshold conductances that endow the pre-BötC with rhythmogenic properties and represent targets for modulatory control of inspiratory rhythm generation.
分析神经回路功能的一个核心问题是确定神经元的内在电导如何对网络活动的产生做出贡献。我们使用实时钙活性成像结合全细胞膜片钳记录，来分析新生大鼠离体脑干切片制备中呼吸前包钦格复合体（pre-BötC）兴奋性节律产生网络中亚阈值电导的贡献。对成像的pre-BötC神经元进行电压钳斜坡记录显示，持续性钠电流（NaP）和以钾离子为主的漏电流主要促成亚阈值电流-电压关系。我们量化了pre-BötC内吸气神经元的两种主要电生理表型，即内在振荡爆发神经元和内在非爆发神经元中的NaP和漏电导密度（g/C(m)）。内在爆发神经元的g(NaP)密度显著更高，而内在爆发神经元和非爆发神经元之间的漏电导密度没有显著差异。通过在pre-BötC内直接进行药理学操作来调节g(NaP)和/或g(Leak)，我们可以在很宽的动态范围内调节网络振荡频率，并导致振荡状态和静息状态之间的转变。这些结果与pre-BötC兴奋性网络模型一致，该模型由内在爆发神经元和非内在爆发神经元的异质混合物组成，其中包含g(NaP)和g(Leak)，其参数值是通过实验获得的。我们提出了一个范式，即NaP和漏电代表了一组功能性的亚阈值电导，赋予pre-BötC节律生成特性，并代表了吸气节律生成调节控制的靶点。
