Synaptic Dialogue: Plasticity Leading to Memory Storage

Northwestern University, Evanston IL

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Abstract

The proposed research is directed at the study of growth-associated protein GAP-43, an essential presynaptic protein with critical functions in neural development (axonal pathfinding), and plasticity (long-term potentiation, learning and memory). Because GAP-43 is central to plasticity mechanisms, brain site-selective manipulations targeting GAP-43 in a temporally and spatially controlled fashion can offer unique insights into memory acquisition, storage and recall. GAP-43 is critical for brain development as its knockout is perinatal lethal probably because the null mutation disrupts synaptic targeting (see Benowitz and Routtenberg, 1997, for review). GAP-43 bidirectionally regulates adult memory: reduction by half impairs (Rekart et aI., 2005), while its overexpression can enhance (Routtenberg et aI., 2000), information storage processes. The proposed research tests the over-arching Aim that in wild type animals the level of endogenous phosphorylatable GAP- 43 plays a pivotal role in regulating brain information storage. Evidence in support of this hypothesis has been gained in transgenic animals, yet no information is currently available as to the site specificity of the phenotype. The specific questions we will address are: What level of region-specific knockdown in GAP-43, using RNAi methods, in adult wild type rodents will impair acquisition or retention of 3 different learning tasks? The siRNA will be delivered using lipofectamine or lentiviral transfer, with bilateral intracranial injections targeting hippocampus, amygdala, anterior cingulate cortex or medial prefrontal cortex. We will thus determine the kinetics of this silencing using RNAi methods to deliver the knockdown targeting nodal points in the 'memory circuit'at different time points in the learning and retention process to pinpoint the mnemonic function served by GAP-43 in each brain location.