High-frequency transmission in the superior olivary complex: molecular regulation by presynaptic proteins

许多听觉脑干神经元能够在长时间内保持高带宽、高频率的放电。例如，投射到外侧上上级橄榄（LSO）的兴奋性（多巴胺能）和抑制性（甘氨酸能）神经元通过耳间强度检测形成声音定位的基础，驱动它们的突触后靶神经元达到约100 μ m。每秒六百次。我们已经表明，在这些突触的快速突触传递是非常强大的持续刺激期间，证明了耐疲劳和低故障率。这些特征使它们有别于“传统”突触，后者抑制更深，频率更低，从抑制状态恢复的效率也低得多。显然，听觉突触利用非常有效的囊泡补充来不知疲倦地编码声音。突触性能差异的潜在分子机制尚不清楚。我们希望通过关注突触前释放机制中的四种关键蛋白来分析LSO神经元高频突触传递的分子调控，这四种蛋白似乎是递质释放速度和保真度的决定因素（巴松，Munc 13 -1，Synaptotagmin 2，CAPS 1）。因果关系将通过特定基因缺失来证明。为了避免与系统性基因缺失相关的问题，我们将进行空间限制性基因切除，这是最近才通过产生候选分子的floxed基因的转基因小鼠而实现的。将通过病毒转染经由立体定位基因递送（Cre重组酶）来追求时间和空间限制的基因沉默。作为基准，我们还将分析海马结构中的两种突触类型，即从内嗅皮层到齿状回的海马CA 3-CA 1连接和GABA能连接。我们将量化基本的突触传递以及突触可塑性与电池建立刺激协议。我们假设，强大的高频传输和突触疲劳的阻力表现为突触前释放机制的突触特异性特征。我们还建议，四个候选蛋白质的贡献的方式，重叠只有部分与他们的同行蛋白质，从而实现适度的冗余。包括光镜和电镜免疫组织化学的组织学研究将补充我们的生理分析。总之，我们期望更好地了解高频神经传递的潜在机制，并阐明突触功能中一些关键参与者的作用。我们的计画也将有助于了解各种神经系统中突触讯息传递的一般情形。

Many auditory brainstem neurons are able to maintain high-bandwidth, high-frequency firing over prolonged periods of time. For example, excitatory (glutamatergic) and inhibitory (glycinergic) neurons projecting to the lateral superior olive (LSO), which form the basis of sound localization via interaural intensity detection, drive their postsynaptic target neurons up to ca. 600 times per second. We have shown that fast synaptic transmission at these synapses is remarkably robust during sustained stimulation as evidenced by resistance to fatigue and low failure rates. These features set them apart from "conventional" synapses, which depress more profoundly and at significantly lower frequency, and recover much less efficiently from their depressed state. Apparently, auditory synapses employ very efficient vesicle replenishment to indefatigably encode sound. The underlying molecular mechanisms for the differences in synaptic performance are unknown. We want to analyze the molecular regulation of high-frequency synaptic transmission to LSO neurons by focusing on four key proteins in the presynaptic release machinery which appear to be determinants of the speed and fidelity of transmitter release (Bassoon, Munc13-1, Synaptotagmin2, CAPS1). Causal relationship will be demonstrated by specific gene deletion. To circumvent problems immanent to systemic gene deletion, we will perform spatially restricted gene ablation, which became available only very recently through the generation of transgenic mice with floxed genes for the candidate molecules. Temporally and spatially restricted gene silencing will be pursued via stereotaxic gene delivery (Cre recombinase) through viral transfection. As a benchmark, we will also analyze two synapse types in the hippocampal formation, namely the glutamatergic CA3-CA1 connection and the GABAergic connection from the entorhinal cortex to the dentate gyrus. We will quantify basic synaptic transmission as well as synaptic plasticity with a battery of established stimulus protocols. We hypothesize that robust high-frequency transmission and resistance to synaptic fatigue are manifested by synapse-specific characteristics in the presynaptic release machinery. We also suggest that the four candidate proteins contribute in a manner that overlaps only partially with their peer proteins, thereby achieving a moderate degree of redundancy. Histological investigations comprising light and electron microscopic immunohistochemistry will complement our physiological analyses. In total, we expect to better understand the underlying mechanisms for high frequency neurotransmission and to elucidate the role of some key players in synapse function. Our project shall also contribute to comprehending general aspects of synaptic information transfer in various neuronal systems.