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

突触强度在毫秒到分钟的时间内受到活动依赖性变化的影响， 称为短期突触可塑性（STSP）。STSP对执行的计算有直接影响， 神经回路，必须了解才能充分了解大脑功能。突触环境受到 显著的活性依赖性pH波动，但其对pH敏感机制的影响 神经传递很少被考虑，尽管它们可能影响STSP的多种机制。 我们已经开发出荧光基因编码的pH指示剂，允许pH的单一动作电位分辨率 果蝇NMJ突触间隙的动力学。我们的初步数据显示， 缝隙碱化（见初步数据），这很可能也发生在脊椎动物的突触， 利用Ca~（2+）/H~+交换质膜Ca~（2+）-ATPase（PMCA）。此外，我们的初步数据表明， 裂缝碱化增强量子大小和Ca2+的进入在突发射击。我们的长期目标是 阐明pH波动纳入STSP机制的手段。在本提案中，我们 将检验活动依赖性裂隙碱化已被纳入增益的假设 在爆发性放电期间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，突触前电压门控 碱化可增强Ca2+通道（VGCC）和突触后离子型谷氨酸受体（iGluRs） 在它们的细胞外表面。 我们的研究战略分为三个独立的目标： 目的1：阐明突触间隙碱化对爆发性突触前Ca~（2+）内流的影响。 目的2：阐明突触间隙碱化影响猝发过程中量子大小的机制。 目的3：研究神经递质释放对个别活动区裂隙pH值变化的影响。 在这里，我们开发了一个测试床，用于研究活性依赖性pH波动对机制的贡献 潜在的STSP。除了直接用于实现上述目标外，我们开发的试剂还将 可用于后续研究pH敏感性STSP机制对电路功能的贡献 以及果蝇的行为，这可能为我们深入了解具有酸碱失衡的神经系统疾病提供了帮助。 例如癫痫和某些智力残疾。

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.