Memory retrieval is a dynamic aspect of memory formation that either reinforces or alters stored memories through reconsolidation or extinction. Although several signaling pathways including the MAP kinase (MAPK) cascade are implicated in retrieval, the underlying signaling events are incompletely defined. The general objective of this grant is to identify signaling elements that contribute to retrieval of hippocampus-dependent, contextual memory. These studies may lead to the identification of specific drug target sites that can be exploited to modify memory retrieval. This proposal is based upon observations made by this lab that implicate PI3 kinase and MAPK in contextual memory retrieval. We discovered that PI3 kinase is activated in several areas of the hippocampus including areas CA1, CA3 and the dentate gyrus during retrieval of contextual memory. Furthermore, inhibition of PI3 kinase in area CA1 of the hippocampus in vivo reversibly blocked contextual memory retrieval. In addition, inhibitors of PI3 kinase blocked increases in MAPK activity associated with memory retrieval. This suggests that activation of PI3 kinase in the hippocampus is critical for memory retrieval and may be required for activation of MAPK during retrieval. Our data also indicate that cAMP-dependent protein kinase (PKA) activity is required for retrieval of contextual memory. There are a number of unanswered questions concerning the role of PI3 kinase in memory retrieval and the relationship between PI3 kinase signaling and other signaling events during retrieval. What is the mechanism for activation of PI3 kinase during retrieval of contextual memory? Are PI3 kinase and MAPK activated in the same neurons during contextual memory retrieval? Are the same neurons in the hippocampus activated during acquisition and retrieval of contextual memory? Is PKA activated in retrieval? Is Akt activity required for memory retrieval? Is activation of PI3 kinase in area CA3 or the dentate gyrus (DG) also required for contextual memory retrieval?
This grant focuses on the molecular events underlying memory retrieval, a fundamental step in information processing. This study may identify drug target sites that can be used to modulate memory retrieval and be useful clinically. For example, drugs that impair memory retrieval may be used in the treatment of phobias.
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