AMPA-type glutamate receptors (AMPARs) exist in various multimeric combinations of glutamate receptor proteins 1-4 (GluR1-4). AMPARs that lack the GluR2 subunit are commonly referred to as calcium- permeable AMPARs (CP-AMPARs) due to their unique conductance properties, and are recruited to synapses during in vitro and in vivo synaptic strengthening under some circumstances. However, many questions remain about the relevance of this form of plasticity to the modification of behavior. In particular, studies have not addressed the role of CP-AMPARs in the formation of associative memory, which occurs by synapse-specific strengthening of glutamatergic transmission. Preliminary data indicate that CP- AMPARs exist at thalamic inputs to the lateral amygdala (LA) of mice, a key site of synaptic modification in associative fear memory. It is hypothesized that additional pools of CP-AMPARs exist in LA neurons or may be synthesized in response to behavioral activation;and that synaptic incorporation and removal of these receptors may play a role in acquisition and erasure of fear memory, respectively. This project will test our predictions based on preliminary data that removal or extrasynaptic retention of GluR2-containing AMPARs by protein-interacting with C-kinase-1 (PICK1) facilitates the synaptic expression of CP-AMPARs, and that this mechanism is required for fear memory. Since preliminary experiments indicate that CP-AMPARs are selectively displaced from synapses by long-term depression (LTD), experiments will examine the molecular events that mediate this process and determine whether they contribute to behavioral extinction of fear memory. Towards these aims, biochemical fractionation of LA protein homogenates and 2-photon glutamate uncaging at spine excitatory synapses will be used to study the molecular and anatomical bases of CP-AMPAR currents, while conventional whole-cell electrophysiology will be used to detect synaptic CP- AMPARs at increasing intervals after auditory fear conditioning. Mouse mutants will be employed to test the role of PICK1 and GluR2 phosphorylation in receptor trafficking and memory retrieval. Since we reason that CP-AMPARs will likely be found to contain GluR1, dephosphorylation of GluR1 will be examined as a mechanism for CP-AMPAR removal during depotentiation and fear extinction using GluR1 phosphomutant and phosphomimetic mice.
These aims will further our understanding of processes underlying memory formation and erasure, and by extension our ability to effectively treat memory impairments. In addition, these experiments may lead to new therapeutic strategies for intervention in debilitating disorders of human anxiety, which are characterized by abnormally high levels of amygdala activity.
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|Anggono, Victor; Clem, Roger L; Huganir, Richard L (2011) PICK1 loss of function occludes homeostatic synaptic scaling. J Neurosci 31:2188-96|
|Clem, Roger L; Huganir, Richard L (2010) Calcium-permeable AMPA receptor dynamics mediate fear memory erasure. Science 330:1108-12|
|Clem, Roger L; Anggono, Victor; Huganir, Richard L (2010) PICK1 regulates incorporation of calcium-permeable AMPA receptors during cortical synaptic strengthening. J Neurosci 30:6360-6|
|Tran, Tracy S; Rubio, Maria E; Clem, Roger L et al. (2009) Secreted semaphorins control spine distribution and morphogenesis in the postnatal CNS. Nature 462:1065-9|