Localized increases in neural activity lead to localized increases in cerebral blood flow. Many potential mediators of this functioning coupling have been investigated over the past century, yet the precise mechanism of functional hyperemia remains unclear. We propose that the excitatory neurotransmitter, glutamate, stimulates the production of epoxyeicosatrienoic acids (EETs) from arachidonic acid by the expoxygenase activity of cytochrome P450 2C11 in astrocytes. The cerebral microcirculation is completely surrounded by astrocyte processes, and astrocyte-derived EETs may act as intraparenchymal, paracrine vasodilators. In support of this hypothesis, previous work has shown that a) cultured astrocytes express cytochrome P450 2C11, b) P450 epoxygenase inhibitors and antisense oligonucleotides of 2C11 inhibit glutamate stimulation of EET production in cultured astrocytes and glutamate-evoked cerebral vasodilation in vivo, and c) submicrocellular concentration of EETs increase K+ currents in cerebral vascular smooth muscle of intraparenchymal microvessels. In the present proposal, we will determine if the action of glutamate on EET production in astrocyte culture is mediated by specific glutamate receptor subtypes and if actions of these receptor subtypes generates a transferable substance capable of hyperpolarizing parenchymal smooth muscle. Parallel studies will be done in vivo in rat brain with microdialysis to determine if action of different types of glutamate receptor causes increased EET release and local increases in tissue blood flow, both of which are blocked by different types of epoxygenase inhibitors nd by chronic administration of antisense oligonucleotides. We will also determine if increased expression of cytochrome P450 2C11 augments EETs-dependent vasodilation to glutamate receptor activation. Physiological activation of blood flow in the whisker barrel cortex by vibrissal stimulation has been reported to be partially attenuated by nitric oxide synthase (NOS) inhibitors by some, but not all investigators. We will investigate the role of the epoxygenase pathway in this functional hyperemic response by using pharmacologic probes and molecular strategies to decrease and increase expression of 2C11. Lastly, in mice deficient in the neuronal NOS isoform, the cortical blood flow response to vibrissal stimulation is fully intact and not inhibited by nitroarginine thereby suggesting up regulation of another pathway. We will determine if cytochrome P450 2C11 epoxygenase activity represents this up-regulated pathway. These interdisciplinary studies will utilizing a variety of molecular, biochemical and physiological techniques to delineate the importance of a novel pathway in astrocytes linking neuronal activity to microcirculatory blood flow regulation.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Program Projects (P01)
Project #
5P01HL059996-03
Application #
6430881
Study Section
Project Start
2001-04-01
Project End
2002-03-31
Budget Start
Budget End
Support Year
3
Fiscal Year
2001
Total Cost
$282,412
Indirect Cost
Name
Medical College of Wisconsin
Department
Type
DUNS #
073134603
City
Milwaukee
State
WI
Country
United States
Zip Code
53226
Gebremedhin, Debebe; Zhang, David X; Carver, Koryn A et al. (2016) Expression of CYP 4A ?-hydroxylase and formation of 20-hydroxyeicosatetreanoic acid (20-HETE) in cultured rat brain astrocytes. Prostaglandins Other Lipid Mediat 124:16-26
Pabbidi, Mallikarjuna R; Mazur, Olga; Fan, Fan et al. (2014) Enhanced large conductance K+ channel activity contributes to the impaired myogenic response in the cerebral vasculature of Fawn Hooded Hypertensive rats. Am J Physiol Heart Circ Physiol 306:H989-H1000
Gebremedhin, Debebe; Gopalakrishnan, Sandeep; Harder, David R (2014) Endogenous events modulating myogenic regulation of cerebrovascular function. Curr Vasc Pharmacol 12:810-7
Carver, Koryn A; Lourim, David; Tryba, Andrew K et al. (2014) Rhythmic expression of cytochrome P450 epoxygenases CYP4x1 and CYP2c11 in the rat brain and vasculature. Am J Physiol Cell Physiol 307:C989-98
Gebremedhin, Debebe; Terashvili, Maia; Wickramasekera, Nadi et al. (2013) Redox signaling via oxidative inactivation of PTEN modulates pressure-dependent myogenic tone in rat middle cerebral arteries. PLoS One 8:e68498
Wickramasekera, Nadi T; Gebremedhin, Debebe; Carver, Koryn A et al. (2013) Role of dual-specificity protein phosphatase-5 in modulating the myogenic response in rat cerebral arteries. J Appl Physiol 114:252-61
Yang, Zeng-Jin; Carter, Erin L; Kibler, Kathleen K et al. (2012) Attenuation of neonatal ischemic brain damage using a 20-HETE synthesis inhibitor. J Neurochem 121:168-79
Renic, Marija; Kumar, Suresh N; Gebremedhin, Debebe et al. (2012) Protective effect of 20-HETE inhibition in a model of oxygen-glucose deprivation in hippocampal slice cultures. Am J Physiol Heart Circ Physiol 302:H1285-93
Liu, Xiaoguang; Li, Chunyuan; Falck, John R et al. (2012) Relative contribution of cyclooxygenases, epoxyeicosatrienoic acids, and pH to the cerebral blood flow response to vibrissal stimulation. Am J Physiol Heart Circ Physiol 302:H1075-85
Terashvili, M; Sarkar, P; Nostrand, M V et al. (2012) The protective effect of astrocyte-derived 14,15-epoxyeicosatrienoic acid on hydrogen peroxide-induced cell injury in astrocyte-dopaminergic neuronal cell line co-culture. Neuroscience 223:68-76

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