Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism
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J. Cereb. Blood Flow Metab. · Aug 2002
Origin of negative blood oxygenation level-dependent fMRI signals.
Functional magnetic resonance imaging (fMRI) techniques are based on the assumption that changes in spike activity are accompanied by modulation in the blood oxygenation level-dependent (BOLD) signal. In addition to conventional increases in BOLD signals, sustained negative BOLD signal changes are occasionally observed and are thought to reflect a decrease in neural activity. In this study, the source of the negative BOLD signal was investigated using T2*-weighted BOLD and cerebral blood volume (CBV) techniques in isoflurane-anesthetized cats. ⋯ The CBV changes in area 18 were faster than the BOLD signals from the same corresponding region and the CBV changes in the suprasylvian gyrus. The results support the notion that reallocation of cortical blood resources could overcome a local demand for increased cerebral blood flow induced by increased neural activity. The findings of this study imply that caution should be taken when interpreting the negative BOLD signals as a decrease in neuronal activity.
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J. Cereb. Blood Flow Metab. · Jul 2002
Hypothermic reperfusion after cardiac arrest augments brain-derived neurotrophic factor activation.
Induction of mild hypothermia improves neurologic outcome after global cerebral ischemia. This study measured levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in hippocampal tissue of rats after resuscitation from 8 minutes of normothermic, asphyxial cardiac arrest. After resuscitation, rats were maintained either at normal temperature (37 degrees C) or cooled to mild hypothermia (33 degrees C, beginning 60 minutes after resuscitation). ⋯ Increased BDNF levels were correlated with activation of the extracellularly regulated kinase (ERK), a downstream element in the signal transduction cascade induced by BDNF. In contrast to the many deleterious processes during ischemia and reperfusion that are inhibited by induced hypothermia, increasing BDNF levels is a potentially restorative process that is augmented. Increased activation of BDNF signaling is a possible mechanism by which mild hypothermia is able to reduce the neuronal damage typically occurring after cardiac arrest.
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J. Cereb. Blood Flow Metab. · Jun 2002
Magnetic resonance angiography of thromboembolic stroke in rats: indicator of recanalization probability and tissue survival after recombinant tissue plasminogen activator treatment.
Magnetic resonance angiography (MRA) was performed in a thromboembolic stroke model of the rat to characterize intracranial vessel occlusion patterns and to test its predictive power for tissue recovery after recombinant tissue plasminogen activator (rt-PA) treatment. After rt-PA-treated selective middle cerebral artery (MCA) occlusion, full recanalization was observed in two of three animals, whereas additional occlusion of the circle of Willis (CW) resulted in full vascular flow restitution in only one of six rats. ⋯ Correspondingly, T2 relaxation time increased to 107% to 118% of control after selective MCA occlusion and to 112% to 124% after combined MCA/CW occlusion in these regions. The present investigation shows that MRA provides valuable information on the severity of thromboembolic stroke and has the power to predict, before the initiation of treatment, the functional tissue outcome after rt-PA-induced thrombolysis.
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J. Cereb. Blood Flow Metab. · Jun 2002
Correlation between cerebral blood flow, substrate delivery, and metabolism in head injury: a combined microdialysis and triple oxygen positron emission tomography study.
Microdialysis continuously monitors the chemistry of a small focal volume of the cerebral extracellular space. Conversely, positron emission tomography (PET) establishes metabolism of the whole brain, but only for the duration of the scan. The objective of this study was to apply both techniques to head-injured patients simultaneously to assess the relation between microdialysis (glucose, lactate, lactate/pyruvate [L/P] ratio, and glutamate) and PET (cerebral blood flow [CBF], cerebral blood volume, oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen) parameters. ⋯ There was no significant relation between CBF and the microdialysis parameters. Moderate short-term hyperventilation appeared to be tolerated in terms of brain chemistry, although no areas were sampled by microdialysis where the OEF exceeded 70%. Hyperventilation causing a reduction of the arterial carbon dioxide tension by 0.9 kPa resulted in a significant elevation of the OEF, in association with a reduction in glucose, but no significant elevation in the L/P ratio or glutamate.
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J. Cereb. Blood Flow Metab. · Jun 2002
Hypoxia-inducible factor-1alpha accumulation in the brain after experimental intracerebral hemorrhage.
Hypoxia-inducible factor-1 (HIF-1), a transcription factor composed of HIF-1alpha and HIF-1beta protein subunits, has been implicated in cellular protection and cell death in cerebral ischemia. The extent to which HIF-1 plays a role in brain pathology during intracerebral hemorrhage (ICH) is unknown. This study determined whether HIF-1alpha is upregulated at different time points in a rat model of ICH and the role of thrombin and red blood cell lysis in upregulation. ⋯ This study demonstrates that perihematomal HIF-1alpha protein is upregulated after ICH. This phenomenon is an early response of brain parenchyma to the clot. Thrombin and erythrocyte lysate are involved in HIF-1alpha upregulation through reducing HIF-1alpha degradation.