Integrin and LTP Consolidation

整合素和LTP巩固如果在诱导后的几分钟内施加低频传入刺激，长期增强（LTP）就会消失。这种效应是突触特异性的，当应用于未增强的突触时，反向刺激只有短暂的效果。缺氧、降温或腺苷输注也可逆转增强。LTP在诱导后的30分钟内逐渐变得不那么容易受到干扰，这一时间框架与许多实验范式中记忆“巩固”的时间框架相当。本研究验证了一个假设，即整合素是一个异二聚体跨膜粘附受体家族，在LTP的稳定（或“巩固”）中起关键作用。整合素是潜伏的，直到出现适当的激活刺激。激活的整合素结合到细胞外基质，重组膜下细胞骨架，并启动信号级联反应。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小时内稳步向基线衰减。所提出的研究的第一个目标是验证预测，即不同的整合素拮抗剂将以与其阻断基质结合的相对效力相对应的相对效力阻止LTP巩固。预计这些实验还将提供关于哪些整合素参与LTP以及它们是否参与巩固过程的不同阶段的信息。第二个目标是绘制整合素在海马区CA1中的分布。原位杂交、免疫细胞化学和共沉淀研究结果表明，4-6个整合素在海马中表达。将使用光镜和电子显微镜相结合的实验来确定这些受体在树突场内重叠的程度。第三个目的是验证用于诱导LTP的θ模式刺激将激活海马整合素的预测。免疫细胞化学法检测局灶黏附激酶（FAK）的自磷酸化将用于检测整合素的激活。阻断LTP的整合素拮抗剂是否也会减少θ刺激引起的FAK磷酸化也将进行测试。第四个目的是测试先前报道的促进或延缓LTP稳定的调节受体是否也促进或延缓NMDA受体对整合素的激活。预计这四组研究将有助于阐明LTP的一个关键但知之甚少的方面，为增强效应如何表达的想法提供新的限制，并对记忆的基本特性产生新的假设。

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.