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.
