Memory Enhancement by a Genetic Increase in cAMP Signals

University Of Washington, Seattle WA

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Abstract

DESCRIPTION (provided by applicant): Consolidation of hippocampus-dependent memory depends on de novo transcription and translation. One of the transcriptional pathways required for consolidation of hippocampus-dependent memory is CRE-,mediated transcription. Calmodulin (CaM)-stimulated adenylyl cyclases, and Erk/MAP kinase (MAPK) plays a major role in calcium activation of CRE-mediated transcription during formation of memory. This proposal focuses on the role of CaM-stimulated adenylyl cyclases in memory and the mechanism for enhanced memory exhibited by mice over-expressing AC1 in the forebrain (AC1+ mice). It is based upon several observations made by this lab including the discovery that CaM-stimulated adenylyl cyclases are required for consolidation of hippocampus-dependent memory, as well as the persistence of remote contextual memory. We also discovered that the nuclear translocation and activation of MAPK during contextual memory formation depends upon CaM-stimulated adenylyl cyclases. We found that the persistence of contextual memory may be maintained by the circadian oscillation of the cAMP/MAPK/MSK1/CREB transcriptional pathway in the hippocampus, an oscillation which depends upon CaM-stimulated adenylyl cyclases. Therefore, we made a transgenic mouse strain over-expressing AC1 in the forebrain, AC1+ mice. Young AC1+ mice have superior memory for novel objects and social recognition and more persistent remote contextual memory. However, the spatial memory of old AC1+ mice is inferior to old wild-type littermates, yet unaffected in young AC1+ mice. We propose that CaM-stimulated adenylyl cyclase activity is required for memory consolidation and memory persistence because it supports the activation and nuclear translocation of MAPK during memory formation and the circadian oscillation of MAPK activity in the hippocampus required to maintain memory. We propose that the stronger memory exhibited by young AC1+ mice may be due to enhanced signaling through the cAMP/MAPK/ MSK-1/CREB signaling pathway as well as amplification of the circadian oscillation of this pathway. We propose that the circadian oscillation of MAPK in the hippocampus may be due to circadian oscillation of CaM-stimulated adenylyl cyclases in the hippocampus.