Intrinsic Plasticity and Information Storage in Cerebellar Purkinje Cells

项目总结： 联想学习依赖于突触输入的加强，这些突触输入在 延长的时间段。一个值得注意的例外是小脑的有监督的联想学习。 平行纤维(PF)-浦肯野细胞突触，其活动预测攀升纤维(CF)介导的错误信号， 经历长期抑郁(LTD)。由于浦肯野细胞是抑制性神经元，经典的Marr-Albus-Ito 小脑功能学说认为，在谷氨酸能Pf输入的LTD引起靶细胞去抑制 小脑核团，从而使运动学习成为可能。然而，最近的证据挑战了 LTD是支持联想运动学习的唯一或主要的细胞机制。例如, 我们实验室的研究结果表明，小鼠的浦肯野细胞在眨眼条件作用后兴奋性增强。 (延迟EBC)，浦肯野细胞特异性敲除SK2型K+通道的小鼠表现出EBC减少。 SK2通道是一种小电导、钙依赖的K+通道，它以一种 非突触(内在)可塑性，增强浦肯野细胞的兴奋性。本征可塑性是共同诱导的 在PF突触进行长时程增强(LTP)。出现了一种情况，在这种情况下，内在的可塑性辅助 增强那些警告即将到来的错误信号的PF输入(不会对其产生影响)可启用EBC 学习，可能与其他PF突触的抑郁平行，其活动继续预测错误 在整个学习过程中发出信号。这种情况符合小脑学习的自适应滤波模型，在该模型中 在教师信号监督下的双向突触权重调整是微调的关键 马达输出。在这里，我们计划使用双光子测量GCaMP6f编码的树枝状钙信号 在清醒小鼠的浦肯野细胞中，测试在EBC期间树突状输入图谱正在重构的假设。 我们预测，这种MAP可塑性不仅包括在某些pF处的响应幅度的抑制 突触，以及在其他PF输入的反应的出现，其活动从预测 无条件刺激(US；眼眶周围呼气)预测发育性眼睑闭合的发生 在EBC期间。我们将研究依赖于SK2的本征可塑性如何有助于反应加强， 重点是树突状钙刺激物在突触稳定和聚集中的可能作用，基序 已被认为是海马区位场形成的重要细胞机制。从基因上使用 阻断固有可塑性(L7-SK2基因敲除)、LTP(L7-PP2B)和LTD(CaMKII T305D)的修饰小鼠， 我们将进一步阐述这些可塑性机制在地图重组中的具体作用 和运动学习。最后，使用体外培养的浦肯野细胞树突和体细胞的双重贴片记录，我们 将研究LTP和内在可塑性之间的相互作用机制，这两种机制似乎是共存的 在EBC中相辅相成。我们将测试LTP稳定突触输入的假设，尽管LTP是内在的 可塑性调节突触的外显，即EPSP波幅对棘波输出的预测性控制。

Project Summary: Associative learning rests on the strengthening of synaptic inputs that show coincident activity over extended periods of time. A notable exception is provided by supervised associative learning in the cerebellum. Parallel fiber (PF) - Purkinje cell synapses, whose activity predicts a climbing fiber (CF)-mediated error signal, undergo long-term depression (LTD). Since Purkinje cells are inhibitory neurons, classic Marr-Albus-Ito theories of cerebellar function state that LTD at glutamatergic PF inputs causes disinhibition of target cells in the cerebellar nuclei, thus enabling motor learning. However, more recent evidence challenges the notion of LTD as the only, or the predominant, cellular mechanism underlying associative motor learning. For example, findings from our laboratory show that in mice Purkinje cell excitability is enhanced after eyeblink conditioning (delay EBC), and that mice with a Purkinje cell-specific knockout of SK2-type K+ channels show reduced EBC. SK2 channels are small conductance, calcium-dependent K+ channels that are downregulated in a form of non-synaptic (‘intrinsic’) plasticity, which enhances Purkinje cell excitability. Intrinsic plasticity is co-induced with long-term potentiation (LTP) at PF synapses. A scenario emerges, in which an intrinsic plasticity-assisted potentiation of those PF inputs that warn of an upcoming error signal (without contributing to it) enables EBC learning, possibly in parallel with depression at other PF synapses, whose activity continues to predict the error signal throughout learning. This scenario is in line with an adaptive filter model of cerebellar learning, in which bidirectional synaptic weight adjustment under supervision of a teacher signal is crucial for the fine-tuning of motor output. Here, we plan to use two-photon measurements of GCaMP6f-encoded, dendritic calcium signals in Purkinje cells of awake mice to test the hypothesis that during EBC the dendritic input map is restructuring. We predict that this map plasticity does not only consist of depression of response amplitudes at some PF synapses, but also the emergence of responses at other PF inputs, whose activity shifts from predicting the unconditioned stimulus (US; periorbital airpuff) to predicting the occurrence of the developing eyelid closure during EBC. We will examine how SK2-dependent intrinsic plasticity contributes to response strengthening, with a focus on possible roles of dendritic calcium spikes in synapse stabilization and clustering, motifs that have been identified as important cellular mechanisms in hippocampal place field formation. Using genetically modified mice with blockade of intrinsic plasticity (L7-SK2 knockout), LTP (L7-PP2B) and LTD (CaMKII T305D), respectively, we will further delineate the specific roles of these plasticity mechanisms in map re-organization and motor learning. Finally, using double-patch recordings from Purkinje cell dendrites and somata in vitro, we will examine the mechanisms of interaction between LTP and intrinsic plasticity that both seem to co-exist and complement each other in EBC. We will test the hypothesis that LTP stabilizes synaptic inputs, while intrinsic plasticity regulates synaptic penetrance, i.e. the predictive control of the EPSP amplitude over the spike output.