Following traumatic brain injury and ischemia, the brain swells due to edema resulting in raised intracranial pressure, neurologic deterioration and in the case of severe swelling, death. At present there is no effective treatment for fulminating brain swelling. The long term goal of this project is to identify the mechanisms leading to traumatic brain swelling and to introduce novel therapies to combat the edematous process. In the previous grant period, we studied the energy crisis that accompanies trauma and found that mitochondrial impairment is a contributing factor toward rendering the brain unable to maintain ionic homeostatis leading to cellular swelling. We now believe the fluid does not enter the cell via a compromised blood brain barrier but enters the cell through the astrocytic end feet which are plastered around the microvessels and provide an entry route to the tissue. We now extend our studies in this proposal to further elucidate the pathway for water entry through aquaporin channels in the rat which serve as an alternate gateway for the edema fluid. To this purpose we base our future work on three hypotheses encompassing (1) clarifying the role of aquaporins in traumatic brain injury by identifying the pathway of sodium and water entry into brain after experimental cortical contusion injury. (2) defining the temporal course of AQP4 channel expression after cortical contusion injury during the period of edema formation and resolution and (3) pharmacologically modulating AQP4 channels to prevent water entry utilizing a selective V1a receptor antagonist which suppresses AQP4 upregulation and reduces edema. For these purposes we utilize sodium fluorescein to identify route of sodium entry. We will utilize sodium and potassium ion selective microelectrodes to measure the ionic changes in the extracellular space which play a major role in determining the amount of water entering brain. At the conclusion of the experiments, brain edema and total tissue sodium and potassium will be measured to gauge the effect of the pharmacologic suppression of the AQP4 channels. Using the well established model of cortical contusion to produce injury we will measure the change in AQP4 protein by western blot analysis;characterize the drug induced special changes by immunohistochemistry and confocal microscopy. Taken in concert, these studies will provide a more in depth understanding of the role of aquaporins in brain injury and introduce novel therapeutic approaches for treating brain edema.
At present, there is no effective treatment for brain swelling following traumatic brain injury. Therefore, it is important to determine why the brain swells, what are the mechanisms involved and how can it be treated. This proposal will address the fundamental mechanism of brain swelling and how it can be blocked pharmacologically.
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