Intrinsic plasticity and information storage in cerebellar Purkinje cells

描述（由申请人提供）：大脑的一个标志性特征是其巨大的可塑性，这在一生中学习和存储信息的能力中是显而易见的。一般认为，记忆储存取决于突触强度的变化，如长期增强（LTP）和长期抑制（LTD）。例如，Marr-Albus-Ito理论认为小脑运动学习是由连接浦肯野细胞的平行纤维（PF）突触上的LTD介导的。PF-LTP可能起到逆转机制的作用（Jvrntell and Hansel, 2006）。“突触记忆”最适合作为细胞学习相关，因为它们是经验依赖的，可以是突触特异性的，允许选择性信息存储。然而，在过去的几年里，人们已经清楚地认识到突触可塑性并不是唯一的参与者。固有可塑性的形式（神经元兴奋性的改变）已经被描述，并且可能在信息存储中发挥作用（Hansel等人，2001；Zhang和Linden, 2003； Frick和Johnston， 2005）。但是内在可塑性是如何与LTD和LTP相互作用的，它在学习和记忆中起什么作用？我们计划在小脑浦肯野细胞中解决这些问题。小脑在学习研究中的一个关键优势是其基础电路简单且特征明确，这有助于研究信息存储中不同类型可塑性的相互作用（Hansel et al., 2001）。我们的初步数据显示浦肯野细胞兴奋性的活性依赖性增加，这取决于蛋白磷酸酶（PP1/2A和PP2B）的激活，部分由sk型钙敏感K通道的下调介导。我们观察到，增强的兴奋性上调了浦肯野细胞的自发尖峰放电，这并不改变目标DCN神经元的强直尖峰率，但通过降低信噪比降低了PF突触对浦肯野细胞的影响。在这里，我们提出了四个具体的目标，以进一步表征浦肯野细胞的内在可塑性。首先，我们计划检查参与诱导兴奋性变化的信号级联，包括钙信号，磷酸酶和激酶（包括分别使用PKC， 1CaMKII和PP2B缺陷的突变小鼠）。其次，我们计划寻找其他类型的离子通道（SK通道旁边）介导兴奋性增强。第三，我们希望检查浦肯野细胞兴奋性的增强是否随后改变树突轴和棘中的钙信号，并影响LTD / LTP诱导的可能性（使用共聚焦显微镜）。第四，结合躯体-树突双补丁和钙成像，我们计划确定兴奋性变化的空间维度。该项目是我们长期目标的一部分，旨在揭示（运动）学习的潜在机制，并开发治疗运动学习缺陷和记忆障碍的新模式。为此，我们还将在行为学习任务中测试转基因小鼠（SK通道转基因和PP2B敲除），以研究内在可塑性在小脑运动学习中的作用。人们普遍认为，学习和记忆是由突触传递效力的长期改变介导的，如长期增强（LTP）和长期抑制（LTD）。触发LTP和LTD的信号级联异常可导致学习缺陷，如小脑共济失调，运动协调和运动学习的精细调节受到干扰。在这里，我们建议描述一种新型的非突触可塑性，它与小脑浦肯野细胞内在膜兴奋性的增加有关，并描述其参与运动学习（以及相关的小脑学习缺陷）。

DESCRIPTION (provided by applicant): One of the hallmark features of the brain is its enormous degree of plasticity, which is evident in the ability to learn and store information throughout lifetime. It is generally assumed that memory storage rests on changes in synaptic strength, such as long-term potentiation (LTP) and long-term depression (LTD). For example, Marr-Albus-Ito theories suggest that cerebellar motor learning is mediated by LTD at parallel fiber (PF) synapses onto Purkinje cells. PF-LTP might function as a reversal mechanism (Jvrntell and Hansel, 2006). "Synaptic memories" are optimally suited as cellular learning correlates, because they are experience-dependent and can be synapse-specific, allowing for selective information storage. However, over the last years it has become clear that synaptic plasticity is not the only player on the scene. Forms of intrinsic plasticity (alterations in neuronal excitability) have been described and might play a role in information storage as well (Hansel et al., 2001; Zhang and Linden, 2003; Frick and Johnston, 2005). But how does intrinsic plasticity interact with LTD and LTP, and what role does it play in learning and memory? We plan to address these questions in cerebellar Purkinje cells. A crucial advantage of the cerebellum in learning research is that the underlying circuitry is simple and well-characterized, which is helpful when studying the interaction of different types of plasticity in information storage (Hansel et al., 2001). Our preliminary data demonstrate an activity-dependent increase in Purkinje cell excitability, which depends on the activation of protein phosphatases (PP1/2A and PP2B) and is partially mediated by a down-regulation of SK-type calcium-sensitive K channels. We observed that the enhanced excitability upregulates spontaneous spike firing in Purkinje cells, which does not alter the tonic spike rate of the target DCN neurons, but lowers the impact of PF synapses onto Purkinje cells by reducing the signal-to-noise ratio. Here, we propose four specific aims to further characterize Purkinje cell intrinsic plasticity. First, we plan to examine the signaling cascades involved in the induction of excitability changes, including calcium signaling, phosphatases and kinases (including the use of mutant mice deficient in PKC, 1CaMKII and PP2B, respectively). Second, we plan to search for additional types of ion channels (next to SK channels) mediating the excitability enhancement. Third, we wish to examine whether this potentiation of Purkinje cell excitability subsequently alters calcium signaling in dendritic shafts and spines (using confocal microscopy) and affects the probabilities for LTD / LTP induction. Fourth, using a combination of somato-dendritic double-patching and calcium imaging, we plan to determine the spatial dimension of excitability changes. The suggested project is part of our long-term objective to reveal underlying mechanisms of (motor) learning and to develop novel modes for the treatment of motor learning deficits and memory disorders in general. To this end, we will also test genetically altered mice (SK channel transgenics and PP2B knock-outs) in behavioral learning tasks to study the role of intrinsic plasticity in cerebellar motor learning. PUBLIC HEALTH RELEVANCE it is widely believed that learning and memory are mediated by long-term alterations in the efficacy of synaptic transmission, such as long-term potentiation (LTP) and long-term depression (LTD). Abnormalities in the signaling cascades triggering LTP and LTD can cause learning deficits, such as in cerebellar ataxias, in which the fine-adjustment of motor coordination and motor learning are disturbed. Here, we suggest to characterize a novel type of non-synaptic plasticity, which is associated with an increase in the intrinsic membrane excitability of cerebellar Purkinje cells, and to describe its involvement in motor learning (and related cerebellar learning deficits).