Physiological and morphological properties of Dbx1-derived respiratory neurons in the pre-Botzinger complex of neonatal mice
Physiological and morphological properties of Dbx1-derived respiratory neurons in the pre-Botzinger complex of neonatal mice
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DOI：
10.1113/jphysiol.2012.250118
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发表时间：
2013-05-01
影响因子：
5.5
通讯作者：
Del Negro, Christopher A.
中科院分区：
文献类型：
--
作者：
Picardo, Maria Cristina D.;Weragalaarachchi, Krishanthi T. H.;Del Negro, Christopher A.
关键点中心点转录因子Dbx1在前Botzinger复合体中产生可能产生呼吸节律的神经元。对比分析Dbx1来源的神经元(Dbx1+)和非Dbx1来源的神经元(Dbx1+)有助于阐明呼吸节律产生的细胞基础。中心点在体外，Dbx1+神经元在呼吸周期中更早激活，释放更大幅度的吸气爆发，并表现出比Dbx1神经元更低的流变性。Dbx1+神经元倾向于表达内在性电流IA(瞬时外向A电流)和Ih(超极化激活电流)，这可能有助于兴奋性突触输入的时间总和，而Dbx1+神经元在IA和Ih方面没有明显的表达模式。Dbx1+神经元呈光滑的无刺树突，在横断面上突起，而Dbx1神经元较少地局限在横断面上，有时还表现出棘突。中心点Dbx1+神经元的特性可能有助于呼吸节律的发生，包括与正在进行的网络活动有关的高水平兴奋性和可能促进突触整合的树突特性。摘要哺乳动物的呼吸依赖于吸气相关的节律，该节律是由下部脑干的前Botzinger复合体(PreBotzinger Complex)中的谷氨酸能神经元产生的。相当一部分可能产生节律的BotC前C神经元起源于表达转录因子Dbx1的单一基因系，但节律发生的细胞机制仍不完全清楚。为了阐明这些机制，我们对前BotC中表达Dbx1的神经元(Dbx1+)和非Dbx1衍生的神经元(Dbx1)进行了比较分析。在节律活跃的新生小鼠脑片制备的全细胞记录显示，与Dbx1神经元相比，Dbx1+神经元在呼吸周期中更早激活，并释放更大幅度的吸气爆发。此外，在网络活动的背景下，Dbx1+神经元需要较少的输入电流来放电尖峰(血流底)。在Dbx1+神经元中，代表A电流(IA)和超极化激活电流(Ih)的固有膜特性的表达往往是相互排斥的。而Dbx1神经元电流Ia和Ih的表达则不存在这种关系。共聚焦成像和数字形态重建显示Dbx1神经元上有树突棘，但Dbx1+神经元无刺。Dbx1阳性神经元的形态主要局限于横断面，而Dbx1阳性神经元在矢状面投射树突的程度较大。Dbx1+神经元的节律性可能部分归因于在网络突触活动的背景下更高水平的内在兴奋性。此外，Dbx1+神经元的形态可能有助于来自其他Dbx1+神经元的局部突触输入的时间总和和整合，这些输入主要发生在树突中，这对启动和维持猝发以及吸气相的同步活动可能是重要的。
Key points center dot The transcription factor Dbx1 gives rise to putatively respiratory rhythm-generating neurons in the pre-Botzinger complex. Comparative analysis of Dbx1-derived (Dbx1+) and non-Dbx1- derived (Dbx1) neurons can help elucidate the cellular bases of respiratory rhythm generation. center dot In vitro, Dbx1+ neurons activate earlier in the respiratory cycle, discharge larger magnitude inspiratory bursts and exhibit a lower rheobase compared with Dbx1 neurons. center dot The Dbx1+ neurons tend to express the intrinsic currents IA (transient outward A-current) and Ih (hyperpolarization-activated current) in diametric opposition, which may facilitate temporal summation of excitatory synaptic inputs, whereas the Dbx1 neurons show no significant pattern of expression regarding IA and Ih. center dot The Dbx1+ neurons exhibit smooth, spineless dendrites that project in the transverse plane, whereas the Dbx1 neurons are confined to the transverse plane to a lesser extent and sometimes exhibit spines. center dot The properties of Dbx1+ neurons that may contribute to respiratory rhythmogenesis include a high level of excitability linked to ongoing network activity and dendritic properties that may facilitate synaptic integration. Abstract Breathing in mammals depends on an inspiratory-related rhythm that is generated by glutamatergic neurons in the pre-Botzinger complex (preBotC) of the lower brainstem. A substantial subset of putative rhythm-generating preBotC neurons derive from a single genetic line that expresses the transcription factor Dbx1, but the cellular mechanisms of rhythmogenesis remain incompletely understood. To elucidate these mechanisms, we carried out a comparative analysis of Dbx1-expressing neurons (Dbx1+) and non-Dbx1-derived (Dbx1) neurons in the preBotC. Whole-cell recordings in rhythmically active newborn mouse slice preparations showed that Dbx1+ neurons activate earlier in the respiratory cycle and discharge greater magnitude inspiratory bursts compared with Dbx1 neurons. Furthermore, Dbx1+ neurons required less input current to discharge spikes (rheobase) in the context of network activity. The expression of intrinsic membrane properties indicative of A-current (IA) and hyperpolarization-activated current (Ih) tended to be mutually exclusive in Dbx1+ neurons. In contrast, there was no such relationship in the expression of currents IA and Ih in Dbx1 neurons. Confocal imaging and digital morphological reconstruction of recorded neurons revealed dendritic spines on Dbx1 neurons, but Dbx1+ neurons were spineless. The morphology of Dbx1+ neurons was largely confined to the transverse plane, whereas Dbx1 neurons projected dendrites to a greater extent in the parasagittal plane. The putative rhythmogenic nature of Dbx1+ neurons may be attributable, in part, to a higher level of intrinsic excitability in the context of network synaptic activity. Furthermore, Dbx1+ neuronal morphology may facilitate temporal summation and integration of local synaptic inputs from other Dbx1+ neurons, taking place largely in the dendrites, which could be important for initiating and maintaining bursts and synchronizing activity during the inspiratory phase.