AMPA type glutamate receptors (AMPARs) mediate fast excitatory transmission in the CNS. These receptors can be calcium-impermeable (CI AMPARs) or calcium permeable (CP AMPARs). Because insertion or removal of CI AMPARs at synapses is key to the expression of canonical forms of plasticity, such as LTP (long-term potentiation) and LTD (long-term depression), the trafficking of these receptors has been extensively studied. In various regions of the brain, CP AMPARs have been implicated in important aspects of neuronal function, including development, synaptic plasticity and cell death, yet the mechanisms regulating the synaptic expression of CP AMPARs remain unclear. This project seeks to address this issue by examining the differential trafficking of CI- and CP-AMPARs in cerebellar stellate cells (SCs), where excitatory transmission is mediated mainly by CP AMPARs. Notably, these cells exhibit a novel form of synaptic plasticity triggered by calcium entry through CP-AMPARs and expressed as a switch in synaptic receptor subtype, from CP- to CI-AMPARs. We plan to use high-resolution electrophysiology (whole-cell and outside-out patch clamp recording from SCs) combined with imaging (immunocytochemistry and single quantum dot-based tracking of AMPARs at the cell surface) to address the following questions: (1) Are transmembrane AMPAR regulatory proteins (TARPS) involved in AMPAR trafficking in SCs? These proteins underlie membrane delivery and surface trafficking of CI-AMPARs but how they regulate CP-AMPARs is unknown. (2) What cellular mechanisms underlie the activity-dependent switch in AMPAR subtype at SC synapses? Specifically, how are CI-AMPARs excluded from excitatory synapses in the basal condition and what are the regulated steps leading to their incorporation at synaptic sites – exocytosis and/or lateral diffusion? Understanding these cellular mechanisms will provide key insights into the regulation of CP-AMPARs at central synapses.
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