Modulation of synaptic transmission by coactivation of presynaptic GABAA and GABAB receptors: kinetics, plasticity, and functional consequences

 描述（由申请人提供）：该项目的长期目标是了解突触前受体，特别是GABAA和GABAB受体，如何影响突触传递，细胞计算和神经元回路中的学习。GABAA和GABAB受体在中枢神经系统中的许多兴奋性突触的突触前膜中共表达，其中它们已显示出调节突触传递。然而，以前的研究一般都是在隔离和静态条件下研究每种受体类型的影响。目前尚不清楚这些受体的共激活（可能在体内发生）如何调节突触传递。我们认为，突触前GABA受体的表达是突触的可塑性，突触前GABA受体共同作用，在时间上调节突触传递。 先前的工作已经表明，小脑颗粒细胞的轴突表达突触前GABAA和GABAB受体两者，其分别增加和减少平行纤维突触处的谷氨酸释放（Dittman和Regehr，1996; Stell等人，2007; Pugh和Jahr，2011; Dellal等人，2012年）。使用全细胞膜片钳电生理学和双光子激光扫描显微镜（包括钙成像）的组合，该项目将证明，而不是相互对立，突触前GABAA和GABAB受体一起发挥作用，以暂时调节传输和增强短期可塑性，结果不可能从单独激活任一受体。此外，这项工作将表明，突触前GABA受体的表达受到突触强度长期变化的调节。这项工作将揭示突触可塑性和突触前受体功能的新形式。突触前GABA受体对兴奋性传递的调节可能是平衡中枢神经系统中兴奋和抑制的一般机制，并且该系统的破坏可能有助于与突触失衡相关的神经病症（例如自闭症、精神分裂症和癫痫）的病因学和治疗。目的1：确定GABAA和GABAB受体共激活对囊泡释放的影响。假设：GABAA和GABAB受体的动力学和亲和力的差异不是彼此相反，而是允许它们一起工作以产生对释放概率的双相效应。目的2：确定突触前GABAA和GABAB受体可塑性的条件。假设：突触前GABAA和GABAB受体的表达与突触强度的长期变化相反。目的3：确定突触前GABAA和GABAB受体对突触后放电和突触后可塑性的影响。假设：突触前GABA受体的激活增强了高频活动列车期间的短期易化和抑制，缩小了突触后放电的持续时间和平行纤维突触的长期可塑性窗口。相关性：兴奋和抑制的精确平衡是神经元回路正常运作所必需的，而不平衡与几种神经系统疾病有关，包括自闭症，精神分裂症和癫痫。这项工作将确定兴奋性突触的神经传递是如何被抑制性神经递质GABA调节的。这项工作将奠定基础突触生理学的未来研究调查在这些条件下的兴奋和抑制失调。

 DESCRIPTION (provided by applicant): The long term goal of this project is to understand how presynaptic receptors, specifically GABAA and GABAB receptors, influence synaptic transmission, cellular computation, and learning in neuronal circuits. GABAA and GABAB receptors are co-expressed in the presynaptic membrane of many excitatory synapses in the central nervous system where they have been shown to modulate synaptic transmission. However, previous studies have generally studied the effects of each receptor type in isolation and with static conditions. It is not currently known how co-activation of these receptors, as is likely to happen in vivo, will modulate synaptic transmission. We propose that expression of presynaptic GABA receptors is a plastic property of the synapse and presynaptic GABA receptors function together to temporally modulate synaptic transmission. Previous work has shown that axons of cerebellar granule cells express both presynaptic GABAA and GABAB receptors, which increase and decrease, respectively, glutamate release at parallel fiber synapses (Dittman and Regehr, 1996; Stell et al., 2007; Pugh and Jahr, 2011; Dellal et al., 2012). Using a combination of whole-cell patch clamp electrophysiology and two-photon laser scanning microscopy (including calcium imaging), this project will demonstrate that, rather than opposing one another, presynaptic GABAA and GABAB receptors function together to temporally modulate transmission and enhance short-term plasticity, a result not possible from activation of either receptor alone. Furthermore, this work will show that expression of presynaptic GABA receptors is regulated by long-term changes in synaptic strength. This work will reveal novel forms of synaptic plasticity and presynaptic receptor function. Regulation of excitatory transmission by presynaptic GABA receptors may be a general mechanism of balancing excitation and inhibition in the central nervous system and disruption of this system may contribute to the etiology and treatment of neurological conditions associated with synaptic imbalances, such as autism, schizophrenia and epilepsy. Aim 1: Determine the effects of GABAA and GABAB receptor co-activation on vesicle release. Hypothesis: Rather than opposing one another, differences in kinetics and affinity of GABAA and GABAB receptors allow them to work together to produce a biphasic effect on release probability. Aim 2: Determine the conditions for presynaptic GABAA and GABAB receptor plasticity. Hypothesis: Presynaptic GABAA and GABAB receptor expression is modulated in opposition to long-term changes in synapse strength. Aim 3: Determine the effects of presynaptic GABAA and GABAB receptors on postsynaptic firing and associative (postsynaptic) plasticity. Hypothesis: Activation of presynaptic GABA receptors enhances short-term facilitation and depression during trains of high frequency-activity, narrowing the duration of postsynaptic firing and the window for long-term plasticity at parallel fiber synapses. Relevance: A precise balance of excitation and inhibition is required for proper functioning of neuronal circuits while imbalances have been associated with several neurological conditions, including autism, schizophrenia, and epilepsy. This work will determine how neurotransmission at excitatory synapses is regulated by the inhibitory neurotransmitter, GABA. This work will lay the groundwork of basic synaptic physiology for future studies investigating dysregulation of excitation and inhibition in these conditions.