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

 描述(申请人提供)：这个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、细胞计算和神经元电路中的学习。GABAA和GABAB受体在中枢神经系统中许多兴奋性突触的突触前膜上共同表达，它们被证明在那里调节突触传递。然而，以前的研究一般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同激活如何调节突触传递，这很可能在体内发生。我们认为突触前GABA受体的表达是突触的可塑性，突触前GABA受体共同作用于突触传递。先前的工作表明，小脑颗粒细胞的轴突表达突触前GABAA和GABAB受体，这两种受体分别增加和减少平行纤维突触的谷氨酸释放(Dittman和Regehr，1996；Stell等人，2007；Pugh和Jahr，2011；Dellal等人，2012)。利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，突触前GABAA和GABAB受体共同作用于时间调制传递并增强短期可塑性，而不是彼此对立，这是单独激活任一受体所不可能的结果。此外，这项工作将表明，突触前GABA受体的表达受突触强度的长期变化的调节。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中枢神经系统中平衡兴奋和抑制的一般机制，该系统的破坏可能有助于与突触失衡相关的神经系统疾病的病因和治疗，如自闭症、精神分裂症和癫痫。目的1：探讨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相互对立的，而是允许它们共同作用，对释放概率产生双相效应。目的：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：研究突触前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训练中的短期促进和抑制，缩短了突触后放电的持续时间，并缩短了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，而失衡与几种神经疾病有关，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如何受到抑制性神经递质GABA的调节。这项工作将为未来研究在这些条件下兴奋和抑制的调节失调奠定基础。

 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.