Investigation of mechanisms involved in perinatal asphyxia-induced cerebrovascular dysfunction is important because fetal and neonatal asphyxia can cause of perinatal brain damage and failure of blood flow regulation is a critical component. Carbon monoxide (CO) from astrocyte heme oxygenase (HO) is important in regulation of newborn cerebral circulation and preliminary data suggest HO products can provide cerebrovascular and astrocytic protection from asphyxia-induced damage. The research proposed pursues the unifying hypothesis that, in newborn brain, asphyxia disrupts astrocyte CO signaling and cerebral arteriolar smooth muscle (VSM) Ca2+ signaling and/or BKCa channel activity causing cerebrovascular dysfunction, while elevation of cytoprotective CO and bilirubin limit the dysfunction. To test this hypothesis, four specific hypotheses will be tested using a novel asphyxia model in newborn pigs: 1. Asphyxia injures astrocytes causing loss of CO-mediated dilation of pial arterioles, 2. Asphyxia depresses cerebral VSM CO-induced Ca2+ sparks, BKCa channel activity, and dilation, 3. Reactive oxygen species (ROS) are major contributors to asphyxia-induced astrocyte and VSM injury, and 4. Cytoprotective CO and bilirubin reduce asphyxia-induced ROS and post-asphyxia astrocyte and VSM dysfunction. Techniques will be used that allow investigation of intact newborn cerebral microcirculation in vivo, isolated pressurized cerebral arterioles, and freshly isolated astrocytes, microvessels and smooth muscle cells. Such research is unique by studying intact cerebral circulation, production of CO by intact brain and isolated astrocytes and microvessels, and investigating, at the cellular level, mechanisms responsible cerebral vascular dysfunction. In addition, experimental interventions that may attenuate cerebrovascular malfunction caused by asphyxia are examined. Cranial windows allow observation of microcirculation, collection of cortical CSF and topical application of agonists, precursors and inhibitors. CO production in vivo and in vitro is identified and quantified by gas chromatography-mass spectrometry. Astrocytes, cerebral arterioles, and cerebral arteriole smooth muscle cells isolated from control and post-asphyxia brains allow study of ROS, CO production, arteriolar reactivity, and vascular smooth muscle function. Global cytosolic Ca2+ and Ca2+ sparks in brain slices, intact arterioles and VSM will be studied using fluorescent indicator technology with a dual excitation, single emission system and laser scanning confocal microscopy, respectively. Patch clamp techniques will be used to examine BKCa channel activity. These studies are important because disorders of the cerebral circulation in the newborn period are major causes of sickness and death and can result in lifelong disabilities in survivors.
Asphyxia may cause perinatal brain injury that leads to lifelong disabilities in survivors. The specific focus of this project is on the endogenous mechanisms that prevent loss of cerebral vascular function following asphyxia. Cerebral vascular dysfunction is often an important component in the development of neonatal brain injury. Understanding mechanisms of asphyxia-related loss of cerebral blood flow regulation is essential in improving the long-term neurological outcome of human newborns.
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