Dopamine/glutamate and hypoxic injury in newborn brain

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Our overall hypothesis is that moderate hypoxic/ischemic insult to the brain activates a number of pathways which, if unopposed, lead to apoptotic or necrotic death of neurons (damaging) while others have a protective role, in part by countering the former. The relative activity of these processes determines the outcome. In the present proposal, we will subject the brain of newborn piglets to graded hypoxic/ischemic insults and quantitatively monitor the responses of key intermediates of the putative damaging and protective pathways in the presence and absence of selective blocking and activating agents. Specifically we will test following hypotheses: 1. Hypoxic/ischemic insult alters the phosphorylation of CREB and DARPP-32 in striatum of newborn piglets and this is an important determinant of long term cellular and tissue injury. The pattern of these alterations (direction, magnitude and duration) depends on the severity of insult. 2. The alterations in phosphorylation of CREB and DARPP-32 in striatum of newborn piglets that results from hypoxic-ischemic insult depends on the magnitude of the increase in extracellular dopamine. 3. Dopamine exerts its action on CREB and DARPP-32 phosphorylation through the D1 and D2 receptors. 4. During hypoxia and ischemia/hypoxia the excessive dopamine release potentiates glutamate toxicity and neuronal injury by modulating glutamate receptor activity. 5. Elevated levels of CREB phosphorylation contribute to neuronal survival following hypoxic and ischemic insults by increasing Bcl-2 expression and increasing Bcl-2/Bax ratio. Expression of caspase, a marker of apoptosis, will also be determined in the above models and correlated with the above parameters. Expression of these and other genes coding for metabolic regulators linked to dopamine as well as those contributing to cell survival and death will be screened using DMAmicroarrays. Our work will provide a better understanding the molecular mechanisms responsible for injury/death of brain cells following periods of oxygen deprivation. This understanding will be the basis for more effective treatment of patients who have been subjected to a period(s) of insufficient oxygen delivery to the brain.