My lab has played an important role in showing that adaptations leading to addiction involve glutamate-dependent neuroplasticity. A current focus is to understand how dopamine (DA) released by psychomostimulants influences LTP and LTD. When I submitted my first K02 application (1999), evidence was emerging that LTP involved phosphorylation and synaptic insertion of AMPA receptors. A """"""""Future Direction"""""""" in that application was to set up primary cultures of nucleus accumbens (NAc) neurons to determine if DA receptors could modulate these processes. We found that D1 agonists increase AMPA receptor phosphorylation and surface expression, suggesting that psychostimulants may directly regulate the strength of excitatory synapses. These findings led to a new research direction in my lab, supported by a R37.
Aims are: 1) Characterize glutamate receptor expression in NAc cultures, 2) Characterize regulation of AMPA receptor surface expression by DA and glutamate receptors, 3) Examine the relationship between GluR1 phosphorylation and its surface expression, and 4) Develop methods for coculturing NAc and cortical cells that allow synaptic interactions but preserve the ability to distinguish NAc and cortical cells. Studies supported by this grant have already generated exciting findings. We found that D1 agonists produce GluR1 externalization at extra-synaptic sites, facilitating synaptic insertion in response to subsequent NMDA receptor stimulation. This might promote LTP. However, continued progress, particularly in evaluating the significance of these findings using in vivo models, will require new experimental approaches. I am applying for renewal of my K02 Award to maintain relief from other duties so that I can devote 75% effort to implementing new approaches. There are four directions in which I plan to expand our capabilities: 1) Develop methods for chemical induction of LTP and LTD in cultures to study regulation of AMPA receptor trafficking during these phenomena by D1 receptors. 2) Develop methods for studying AMPA receptor trafficking in animal models of addiction, using a membrane-impermeant cross-linking agent (BS 3) to distinguish between surface-expressed and internal AMPA receptors. 3) Develop collaborative studies with the Midwest Proteome Center to identify proteins associated with surface-expressed AMPA receptors. 4) Continue development of electrochemical methods for monitoring of extracellular glutamate levels in animal models of addiction. I have consulted with internationally recognized experts in the development of these new directions, all of whom will continue to provide training during the Award.
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