Integrin and LTP Consolidation

整合素和LTP巩固长时程增强(LTP如果在诱导后几分钟内施加低频传入刺激则消失。这种效应是突触特有的，当应用于未增强的突触时，反向刺激只有短暂的影响。缺氧、降温或注射腺苷也会逆转这种增强作用。在诱导后的30分钟内，LTP逐渐不太容易受到干扰，这一时间框架与许多实验范式中的记忆“巩固”时间相当。这项拟议的工作验证了一种假说，即整合素是一种异二聚体跨膜黏附受体家族，在LTP的稳定(或巩固)中发挥关键作用。整合素是潜伏的，直到出现适当的激活刺激。激活的整合素与细胞外基质结合，重组亚膜细胞骨架，启动信号级联反应。阻断整合素-基质结合的小肽对LTP的初始阶段没有明显影响，但会导致增强作用在1-2小时内稳定地衰减到基线水平。拟议研究的第一个目标是测试不同的整合素拮抗剂将阻断LTP整合的预测，其相对效力与它们在阻断基质结合中的相对效力相对应。预计这些实验还将提供有关LTP涉及哪些整合素的信息，以及它们是否参与了巩固过程的不同阶段。第二个目标是定位整合素在海马区CA1的分布。原位杂交、免疫细胞化学和共沉淀研究结果表明，4-6整合素在海马区表达。结合光学和电子显微镜实验将被用来确定这些受体在树突域内重叠的程度。第三个目标是测试用于诱导LTP的theta模式刺激将激活海马区整合素的预测。粘着斑激酶(FAK)的自动磷酸化的免疫细胞化学分析将被用于检测整合素的激活。还将测试阻断LTP的整合素拮抗剂是否也能减少由theta刺激引起的FAK磷酸化。第四个目标是测试先前报道的促进或延缓LTP稳定的调节性受体是否也促进或延缓由NMDA受体激活的整合素。预计这四组研究将有助于阐明LTP的一个关键但鲜为人知的方面，为如何表达增强效应提供新的约束，并产生关于记忆的基本属性的新假说。

Integrins and LTP consolidation Long term potentiation (LTP disappears if low frequency afferent stimulation is applied within a few minutes of induction. This effect is synapse specific and the reversing stimulation has only transient effects when applied to unpotentiated synapses. Potentiation is also reversed by hypoxia, cooling, or adenosine infusions. LTP becomes progressively less vulnerable to disruption during the 30 minutes following its induction, a time frame comparable to that for memory 'consolidation' in many experimental paradigms. The proposed work tests the hypothesis that integrins, a family of heterodimeric transmembrane adhesion receptors, play a critical role in the stabilization (or 'consolidation') of LTP. Integrins are latent until presentation of an appropriate activating stimulus. Activated integrins bind to the extracellular matrix, reorganize the submembrane cytoskeleton, and initiate signaling cascades. Small peptides that block integrin-matrix binding have no evident effects on the initial stages of LTP but cause potentiation to decay steadily towards baseline over a period of 1-2 hours. The first objective of the proposed studies is to test the prediction that diverse integrin antagonists will block LTP consolidation with relative potencies that correspond to their relative potencies in blocking matrix binding. It is expected that these experiments will also provide information on which integrins are involved in LTP and whether they are engaged at different phases of the consolidation process. The second objective is to map the distribution of integrins in hippocampal field CA1. Results from in situ hybridization, immunocytochemical, and co-precipitation studies suggest that 4-6 integrins are expressed in hippocampal. A combination of light and electron microscopic experiments will be use to determine the extent to which these receptors overlap within dendritic fields. The third objective is to test the prediction that the theta patterns stimulation used to induce LTP will activate hippocampal integrins. Immunocytochemical assays for autophosphorylation of the focal adhesion kinase (FAK) will be used to test for integrin activation. Tests of whether integrin antagonists that block LTP also reduce the FAK phosphorylation elicited by theta stimulation will also be conducted. The fourth objective is to test if modulatory receptors previously reported to promote or retard the stabilization of LTP also promote or retard integrin activation by NMDA receptors. It is expected that the four groups of studies will help elucidate a critical but poorly understood aspect of LTP, provide new constraints on ideas about how the potentiation effect is expressed, and generate novel hypotheses about a fundamental property of memory.