The broad, long-term goal of this project is to discover the role of Ca2+ permeable AMPA/Kainate (Ca-A/K) channels in selective neurodegeneration of a subpopulation of neurons in the hippocampus following ischemic, epileptic, or traumatic brain injury, and if these channels are also important in some neurodegenerative diseases such as ALS and AD. The Ca2+ permeability of AMPA channels is determined by the presence of the subunit GluR2, which renders AMPA channels impermeable to Ca2+. Previous studies demonstrating the down regulation of GluR2 mRNA and peptide following some forms of brain insult suggests that neuronal death in some cases may be mediated by the formation of new Ca-A/K channels that could lead to excessive Ca2+ or Zn2+ influx, loss of ionic homeostasis, and eventual death. To date, however, no one has demonstrated directly the physiological relevance of the loss of GluR2 protein following insult. We hypothesize that numbers of Ca-A/K channels are dynamically regulated at synaptic sites where they would most likely mediate excessive ion flux, and that in some forms of neurodegeneration, an upregulation in the number of Ca-A/K channels does indeed occur due to the down regulation of GluR2. We first propose to develop a cell culture system to assess presence and numbers of Ca-A/K channels using fluorescent imaging and immunocytochemistry. We will then use this system to assess regulation of functional synaptic Ca-A/K channels following treatment of cultured neurons to injury mimicking conditions, or molecular biological procedures that may potentially alter Ca-A/K channel levels. We also propose to test our hypothesis in vivo, using a kainate induced seizure model to asses synaptic GluR2 levels.
