Although in the last ten years there have been significant inroads into the molecular, cellular and systems mechanisms that mediate the early stages of contextual fear conditioning, a model of emotional memory, later stages of this process remain poorly understood. Recently our laboratory reported genetic, imaging and reversible lesion evidence that supports the idea that long-term memory for contextual conditioning depends on cortical regions, such as the anterior cingulate. Now, we propose to use a combination of genetics, transgenics, electrophysiology and 2-photon in vivo imaging to unravel the molecular and cellular mechanisms of cortical plasticity that underlie remote emotional memory.
The specific aims of Project 1 are: 1- To identify genes specifically required for remote memory for contextual conditioning. In our Reverse Forward Genetic (RFG) pilot screen, out of 55 transgenics and KOs selected with a random number generator from the Jackson Laboratory collection, we found that 2 affect specifically 7-day memory (remote) for contextual conditioning, without disrupting 1-day memory (recent), general activity levels or shock reactivity. We now propose to extend this screen and test contextual fear conditioning in another 350 transgenic and KO mutants. These mutants will then be screened for somatosensory (Project 2) and visual (Project 3) plasticity deficits, as a preamble for mechanistic studies (see below) to unravel the molecular and physiological mechanisms underlying the later stages of cortical and behavioral plasticity. 2- To derive region and temporally specific mutations for genes that affect long-term memory for contextual conditioning. We propose to use the loxP/Cre recombinase system to control the cell types, brain regions and temporal expression of the mutations isolated in aim 1. The resulting mice will be tested for memory deficits and will also be studied in Projects 2 and 3. 3- To uncover cortical molecular mechanisms underlying the turnover and stability of spines in the anterior cingulate. Plasticity, including behavioral plasticity (i.e. remote memory), is thought to involve changes in neuronal structure required for consolidation and stability of stored information. We propose to use 2-photon scanning confocal in vivo imaging to examine whether mutations that affect remote memory also affect turnover and stability of spines in cortical regions required for remote memory (i.e. anterior cingulate) in trained and untrained (contextual conditioning) mutants and controls. These studies will parallel related imaging studies carried out in Projects 2 and 3. All together, the studies described here and related studies in Projects 2 and 3 will unravel fundamental molecular, cellular and structural mechanisms of how the neocortex encodes and stores information. These findings will have a key impact on how we study and treat disorders associated with emotional memory.
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