The impact of synaptic cleft pH fluctuations on short-term synaptic plasticity

突触强度会在几毫秒到几分钟内发生与活动相关的变化，这是一种现象 称为短期突触可塑性（STSP）。 STSP 对执行的计算有直接影响 必须了解神经回路才能充分了解大脑功能。突触环境受 显着的活动依赖性 pH 波动，但它们对潜在的 pH 敏感机制的影响 尽管神经传递可能受到 STSP 背后多种机制的影响，但很少考虑它们。 我们开发了荧光基因编码 pH 指示剂，可实现 pH 值的单一动作电位分辨率 果蝇 NMJ 突触间隙的动力学。我们的初步数据揭示了令人惊讶的程度 裂口碱化（见初步数据），这种情况很可能也发生在脊椎动物的突触处 使用 Ca2 /H 交换质膜 Ca2 -ATP 酶 (PMCA)。此外，我们的初步数据表明 裂隙碱化增强了爆发放电期间的量子尺寸和 Ca2 进入。我们的长期目标是 阐明将 pH 波动纳入 STSP 机制的方法。在本提案中，我们 将检验活性依赖性裂隙碱化已纳入增益的假设 在爆发放电过程中维持神经传递的机制。利用分子遗传学技术， 电生理学和荧光成像我们将测试我们的工作假设，即突触前电压门控 Ca2 通道 (VGCC) 和突触后离子营养型谷氨酸受体 (iGluR) 通过碱化而增强 在裂缝中的细胞外表面。 我们的研究策略分为三个不同的目标： 目标 1：阐明突发期间突触间隙碱化对突触前 Ca2 进入的影响。 目标 2：阐明突触间隙碱化影响突发期间量子大小的机制。 目标 3：研究神经递质释放对各个活动区裂隙 pH 值变化的影响。 在这里，我们开发了一个测试平台，用于研究活性依赖性 pH 波动对机制的影响 底层 STSP。除了直接用于实现上述目标之外，我们开发的试剂还将 对于后续研究 pH 敏感的 STSP 机制对电路功能的贡献很有用 和果蝇的行为，可能有助于深入了解酸碱失衡的神经系统疾病 例如癫痫症和某些智力障碍。

Synaptic strength is subject to activity-dependent changes over periods of milliseconds to minutes, a phenomenon referred to as short-term synaptic plasticity (STSP). STSP has a direct influence on computations performed by neural circuits and must be understood to fully understand brain function. The synaptic environment is subject to significant activity-dependent pH fluctuations but their impact on the pH-sensitive mechanisms underlying neurotransmission is rarely considered despite their likely influence of multiple mechanisms underlying STSP. We have developed fluorescent genetically-encoded pH indicators allowing single action potential resolution of pH dynamics in the synaptic cleft of the Drosophila NMJ. Our preliminary data reveal the surprising extent to which the cleft alkalinizes (see preliminary data) and it is highly likely that this also happens at vertebrate synapses that employ the Ca2+/H+ exchanging plasmamembrane Ca2+-ATPase (PMCA). Furthermore, our preliminary data point to cleft alkalinization potentiating both quantal size and Ca2+ entry during burst firing. Our long-term goal is to elucidate the means by which pH fluctuations are incorporated into STSP mechanisms. Within this proposal we will examine the hypothesis that activity-dependent cleft alkalinization has been incorporated into gain mechanisms that sustain neurotransmission during burst firing. Using molecular genetic techniques, electrophysiology and fluorescence imaging we will test our working hypotheses that presynaptic voltage-gated Ca2+ channels (VGCCs) and postsynaptic ionotrophic glutamate receptors (iGluRs) are potentiated by alkalinization at their extracellular faces in the cleft. Our Research Strategy is broken down into three separate aims: Aim 1: Elucidate the influence of synaptic cleft alkalinization on presynaptic Ca2+ entry during bursts. Aim 2: Elucidate the mechanisms by which synaptic cleft alkalinization affects quantal size during bursts. Aim 3: Investigate the impact of neurotransmitter release on cleft pH change at individual active zones. Here we develop a test bed for investigating the contribution of activity-dependent pH fluctuations to mechanisms underlying STSP. Beyond their immediate employment in addressing the aims above, the reagents we develop will be useful for subsequent investigations into the contribution of pH-sensitive STSP mechanisms to circuit function and behavior in Drosophila, potentially providing insight into neurological disorders with an acid-base imbalance component such as seizure disorders and certain intellectual disabilities.