Excitotoxic damage following ischemic insult is well known to be one of the major causes of cell death following stroke. In spite of the large amount of evidence implicating NMDA receptors in excitotoxicity, NMDA receptor (NMDAR) antagonists have not proven clinically beneficial in the treatment of stroke. This could be due to the fact that too much NMDAR signaling is harmful, but some signaling is necessary and neuroprotective. Thus it is important to dissect the pathways downstream of NMDAR activation so that specific pro-death pathways may be targeted. One way to do this is to identify and investigate proteins that are directly associated with the C-terminal tails of the NMDARs. Indeed, Ca2+ influx through NMDARs promotes cell death more efficiently than through other Ca2+ permeable channels, suggesting that proteins involved in excitotoxic cell death are directly associated with NMDARs. Initial pharmacological data indicate that specific NMDAR subunits, specifically NR2A and NR2B, may play different roles in excitotoxicity. However, the results thus far are confusing and contradictory. This may be due to limitations of pharmacological antagonists which do not address the question of which proteins the individual subunits are specifically recruiting to the synapses and subsequently activating. We propose to specifically investigate the proteins associated with the tails of NR2A and NR2B and to use molecular genetic tools to dissect the roles of NR2A and NR2B in excitotoxicity. We believe these studies will elucidate critical pathways downstream of NMDAR activation that may be targeted therapeutically. Specifically, we will: 1) Determine the roles of the NR2A and NR2B NMDA subunits in excitotoxicity in general, as well as what role they play in the differential sensitivity of subtypes of interneurons to excitotoxicity. Considerable data indicates NR2A and NR2B play differential roles in plasticity and perhaps also excitotoxicity. However, the pharmacological tools that have been used have provided conflicting results. We will use molecular tools to further characterize the roles of these subunits. 2) Screen for a negative regulator of LTP that interacts with the C-terminal tail of NR2A. Our preliminary data indicate a negative regulator of LTP binds specifically to the tail of NR2A and not NR2B. Molecules identified as having a role in LTP may also participate in anoxic LTP, a pathological and harmful form of plasticity resulting from excitotoxic mechanisms.
In spite of the large amount of evidence implicating NMDA receptors in excitotoxicity, NMDA receptor (NMDAR) antagonists have not proven clinically beneficial in the treatment of stroke. This could be due to the fact that too much NMDAR signaling is harmful, but some signaling is necessary and neuroprotective. By identifying and dissecting the individual pathways downstream of NMDAR activation, specific pro-death pathways may be blocked, thus mitigating excitotoxic damage without interfering with neuroprotective NMDAR signaling.