Role of voltage-gated calcium channel alpha2delta subunits for spiral ganglion neurons and afferent auditory processing

听觉通路的毛细胞和神经元使用不同的离子通道、递质受体和突触特化来保证具有极高时间精度的超快信号。这也适用于电压门控Ca 2+通道（VGCC），其是突触前Ca 2+内流和递质释放所需的。VGCC是由成孔α 1亚基、细胞内β亚基和细胞外α 2 δ（α 2d）亚基组成的多聚体蛋白复合物。生物物理学和药理学性质主要由10个α 1亚基之一决定，而β和α 2d亚基有助于VGCC的表面表达和微调通道门控。存在四种不同的a2 d亚基，具有部分冗余和部分特异性功能。我们先前已经证明，a2 d3缺陷的小鼠尽管听力阈值轻微升高，毛细胞的生理和形态正常，但听觉诱发的脑干反应发生了扭曲。a2 d3的缺乏降低了培养的螺旋神经节神经元（SGN）的体细胞Ca ~（2+）电流。听神经纤维到耳蜗核丛状细胞的突触传递受到影响，听神经纤维终末的大小明显减少。此外，这些小鼠在行为任务中无法辨别调幅音调，从而建立了a2 d3缺陷小鼠作为听觉处理障碍的模型。由于a2 d3在传入听觉通路的几个核团中表达超出SGN，我们将通过分析SGN中特别缺乏a2 d3的条件性小鼠模型来剖析a2 d3的特定作用，所述条件性小鼠模型具有（a）Ca 2+电流记录，（B）下丘中神经元的体内记录和（c）听觉辨别学习实验。越来越多的证据表明，a2 d亚基除了仅仅调节通过VGCC的Ca 2+通量外，还发挥其他作用，例如，对于突触前和突触后的结构和功能。由于SGN也表达a2 d1和a2 d2的mRNA，我们将使用a2 d1敲除和a2 d2突变小鼠研究这些a2 d亚基对SGN Ca 2+电流、Ca 2+通道蛋白表达和突触形态的作用。下丘神经元的活体记录将使我们深入了解不同小鼠处理时间信息的能力。最后，行为听觉辨别学习实验将补充a2 d亚基在听觉加工中的作用。

Hair cells and neurons of the auditory pathway use distinct ion channels, transmitter receptors and synapse specializations to guarantee ultrafast signalling with exquisitely high temporal precision. This also applies to voltage-gated Ca2+ channels (VGCC), which are required for presynaptic Ca2+ influx and transmitter release. VGCCs are multimeric protein complexes consisting of a pore-forming alpha1 subunit, an intracellular beta-subunit and an extracellular alpha2delta (a2d) subunit. Biophysical and pharmacological properties are largely determined by one of the ten alpha1 subunits, whereas beta and a2d subunits assist in surface expression of VGCCs and fine-tune channel gating. Four different a2d subunits exist with partially redundant and partially specific functions. We have previously shown that a2d3-deficient mice have distorted auditory evoked brainstem responses despite only mildly elevated hearing thresholds and normal physiology and morphology of hair cells. Lack of a2d3 reduced somatic Ca2+ currents of cultured spiral ganglion neurons (SGN). Synaptic transmission from auditory nerve fibers to bushy cells of the cochlear nucleus was compromised, and sizes of auditory nerve fiber terminals were markedly reduced. Moreover, the mice were unable to discriminate amplitude-modulated tones in a behavioral task, establishing the a2d3-deficient mouse as model for an auditory processing disorder. Because a2d3 is expressed beyond SGN in several nuclei of the afferent auditory pathway, we will dissect the specific roles of a2d3 by analysing a conditional mouse model that specifically lacks a2d3 in SGN with (a) Ca2+ current recordings, (b) in-vivo recordings of neurons in the inferior colliculus and (c) auditory discrimination learning experiments. Evidence is accumulating that a2d subunits play additional roles than merely modulating Ca2+ flux through VGCCs, e.g. for the structure and function of pre- and postsynapses. Because SGN express mRNA for a2d1 and a2d2 as well, we will study the roles of these a2d subunits for SGN Ca2+ currents, Ca2+ channel protein expression and synapse morphology using a2d1 knockout and a2d2 mutant mice. In vivo recordings of neurons in the inferior colliculus will give insights into the ability of the different mice to process temporal information. Finally, behavioral auditory discrimination learning experiments will complement the picture of the role of a2d subunits in auditory processing.