Current Neurovascular Research - Volume 6, Issue 2, 2009

Glucose consumption is severely depressed in the ischemic core, whereas it is maintained or even increased in penumbral regions during ischemia. Conversely, glucose utilization is severely reduced early after reperfusion in spite that glucose and oxygen are available. Experimental studies suggest that glucose hypometabolism might be an early predictor of brain infarction. However, the relationship between early glucose hypometabolism with later development of infarction remains to be further studied in the same subjects. Here, glucose consumption was assessed in vivo by positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG) in a rat model of ischemia/reperfusion. Perfusion was evaluated by PET with 13NH3 during and after 2-hour (h) middle cerebral artery occlusion, and 18F-FDG was given after 2h of reperfusion. Brain infarction was evaluated at 24h. Mitochondrial oxygen consumption was examined ex vivo using a biochemical method. Cortical 18F-FDG uptake was reduced by 45% and 25% in the ischemic core and periphery, respectively. However, substantial alteration of mitochondrial respiration was not apparent until 24h, suggesting that mitochondria retained the ability to consume oxygen early after reperfusion. These results show reduced glucose use at early reperfusion in regions that will later develop infarction and, to a lesser extent, in adjacent regions. Depressed glucose metabolism in the ischemic core might be attributable to reduced metabolic requirement due to irreversible cellular injury. However, reduced glucose metabolism in peripheral regions suggests either an impairment of glycolysis or reduced glucose demand. Thus, our study supports that glycolytic depression early after reperfusion is not always related to subsequent development of infarction.

Bradykinin is one of metabolites produced during myocardial ischemia and infarction that can activate cardiac spinal (sympathetic) sensory neurons to cause chest pain. The aim of this study was 1) to characterize the responses of thoracic superficial and deeper spinal neurons in rats to intrapericardial administration of bradykinin as a noxious cardiac stimulus; 2) to compare neuronal responses to bradykinin alone and a mixture of algogenic chemicals (serotonin, prostaglandin E2, histamine, adenosine and bradykinin) used in a previous study. Extracellular potentials of single neurons in the T3 spinal cord were recorded in pentobarbital anesthetized, paralyzed, and ventilated male rats. A catheter was placed in the pericardial sac to administer 0.2 ml solution of bradykinin (10-5 M, 1 min). The results showed that 10/33 (30%) superficial and 80/165 (48%) deeper spinal neurons responded to intrapericardial bradykinin. All 10 superficial responsive neurons and 72/80 (90%) deeper neurons were excited; 7 (9%) neurons were inhibited; one neuron showed excitation-inhibition response pattern. Of 72 neurons excited by bradykinin, 35 and 47 neurons exhibited short- and longlasting responses patterns, respectively. The proportions of response patterns and maximal excitatory responses to bradykinin were similar to effects obtained with a mixture of algogenic chemicals. However, the time to peak (28.3±3.1 s) and recovery time of long-lasting excitatory responses to bradykinin alone (125.2±8.9 s, n=47) were significantly shorter than the responses of neurons to the algogenic mixture (38.6±3.8 s and 187.5±18.5 s, n=49, P<0.05). In conclusion, bradykinin might play a key role in spinal processing for cardiac nociception, although other components released during ischemia might affect time characteristics of a subtype of thoracic spinal neurons receiving noxious cardiac input.

Subarachnoid hemorrhage (SAH) develops when extravasated arterial blood enters subarachnoid space and mixes with cerebrospinal fluid. As a result, many pathologies develop, including arterial vasospasm that leads to the ischemia and hypoxia. Immuno-inflammatory response is considered as the cause of numerous complications following SAH. In the study, we examined the role of one of major cytokines, interleukin 1-beta (IL-1beta), on the vascular pathologies after experimental SAH in adult rats. SAH was produced by injection of 150 uL of autologous arterial blood into cisterna magna. In 50% of animals, IL-1beta activity was inhibited by intracerebroventricular administration of anti-rat IL-1beta antibodies (SAH' groups). Control group consisted of sham-operated rats. Ninety minutes or 24 hrs following surgery, animals were perfused transcardially and whole brains were collected. Spasm index (ratio of vessel diameter to the mean wall thickness) of basilar artery as well as blood vessel density (number of vessels per square millimeter) at brain stem and frontal part of the brain were measured. SAH led to the vasospasm of basilar artery and increased the density of blood vessel. Neutralization of IL-1beta activity significantly reduced both the vasospasm and blood vessel density only 24 hrs after SAH. The results demonstrate an important role of IL-1beta in the delayed development of vascular pathologies after subarachnoid hemorrhage.

N-methyl-D-aspartate (NMDA) receptors (NMDA-Rs) have different modulatory effects on excitatory synaptic transmission depending on the receptor subtypes involved. The present study investigated the subunit composition of the presynaptic NMDA-Rs in layer II/III pyramidal neurons of the rat visual cortex. We recorded evoked a-amino-3-hydroxy- 5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated excitatory postsynaptic currents (eEPSCs) using wholecell voltage clamp with the open-channel NMDA receptor (NMDA-R) blocker, (+)-5-Methyl-10,11-dihydro-5Hdibenzo( a,d)cyclohepten-5,10-imine hydrogen maleate (MK-801), in the recording pipette. We found that the paired-pulse ratio (PPR) by two successive stimuli with inter-pulse intervals of 50 ms was significantly increased by D-APV, a selective NMDA-R antagonist. Using a specific antagonist for NR2B-NMDA-Rs, (αR,βS)-α-(4-hydroxyphenyl)-β- methyl-4-(phenylmethyl)-1-piperidinepropanol hydrochloride (Ro 25-6981), instead of d-2-amino-5-phosphonovalerate (D-APV), we found that the PPR of eEPSCs was also significantly increased. Moreover, Zn2+, an NR2A-NMDA-R antagonist, did not influence on the PPR. These results suggest that presynaptic NR2B-containing NMDA-Rs are located in layer II/III pyramidal neurons of the rat visual cortex, and that presynaptic NR2B-containing NMDA autoreceptors but not NR2A-containing NMDA autoreceptors mediate glutamate release in the rat visual cortex. Moreover, these findings may be clinically relevant to schizophrenia, where enhancing NMDA-R function is considered to be a promising strategy for treatment of the disease.

In preterm infants, neurological signs and clinical manifestations of brain damage are limited criteria for diagnosis of neurologic sequelae. Early indicators of brain damage are needed and currently some specific biochemical markers of brain injury are investigated to assess regional brain damage after perinatal asphyxia in neonates. In this study Protein S-100 (PS-100) and Neuron Specific Enolase (NSE) serum levels were studied serially during the perinatal period in preterm neonates with perinatal asphyxia as markers of glial and neuronal damage respectively. Thirty outborn preterm infants with perinatal asphyxia were studied at 3, 24, 48 hours and 7 days of life. According to Apgar scores at 1' and cord blood pH and lacticidemia (LA), patients were divided in two groups: 15 of them (GA 33±1.2 wk, BW 1790±383 g) with severe asphyxia (Apgar <4, pH7.0±0.08, LA 6.29±0.79 mM/L) and 15 (GA 32±1.8 wk, BW 1810±290 g) with mild asphyxia (Apgar between 4-6, pH 7.18±0.05, LA 2.59±0.61 mM/L). Ten gestational age matched healthy preterm neonates were studied as control group. Cerebral ultrasound examinations (7 MHz) were performed at birth and repeated at 3 weeks of life. The results of this study show that neonates with severe asphyxia at any time had significantly more elevated mean serum levels of both markers compared to the group with mild asphyxia and to the control group (p<0.05). The values of control group were also significantly lower in comparison with that of mild asphyxia. In neonates with severe asphyxia, NSE values decreased constantly from birth to the seventh day of life, while PS-100 showed a different pattern increasing progressively between 3 h and 7 days. In neonates with mild asphyxia serum values of both markers showed decreasing levels through the study period. The results of this study suggest that perinatal asphyxia is associated with the release of different brain cellular proteins in the blood of preterm infants with different time course indicating specific regional cellular injury. The more elevated levels of NSE at birth found in the newborns with severe asphyxia could be considered as an early biomarker of neuronal necrotic damage in the ischaemic phase of perinatal cerebral hypoxic-ischaemic insult; progressive increase of PS-100 during the first week of life in the same neonates could be expression of apoptotic damage of glial cells occurring in the reperfusion phase of cerebral ischaemia.

This study assessed the neuroprotective effects of angelica injection in the rat sciatic nerve crush injury (SCI). Forty eight male Sprague Dawley rats were randomly divided into 4 groups: one was the sham group (S), which received sham surgery and given saline injection and the others were received SCI surgery and given saline injection, high and low dose angelica injection for 4 weeks, respectively. The sciatic functional index (SFI) in walking-track analysis, conductive velocity (CV), the number of fluorogold labeled motoneurons, and the expression patterns of brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in the sciatic nerve and spine were examined. The results showed that SFI descended gradually on day 7, and dropped more quickly on day 28 in treatment groups (Low and High dose group). The CV in treatment groups was higher than control group (C). The numbers of motoneurons in treatment groups were larger than C group (P<0.05), but less than that in S group (P<0.01). The expressions of BDNF and NGF protein in the groups received SCI surgery were significantly lower than in S group, but the protein expressions in the groups received angelica injections were significantly higher than that in C group (P<0.01). These findings suggested that angelica injection can improve the sciatic nerve crush injury, and the mechanism might be through the increase of BDNF and NGF protein expression.

Acute loss of spinal cord vascularity followed by an endogenous adaptive angiogenic response with concomitant microvascular dysfunction is a hallmark of traumatic spinal cord injury (SCI). Recently, the potent vasoactive factor vascular endothelial growth factor (VEGF) has received much attention as a putative therapeutic for the treatment of various neurodegenerative disorders, including SCI. Exogenous VEGF exerts both protective and destabilizing effects on microvascular elements and tissue following SCI but the role of endogenous VEGF is unclear. In the present study, we systemically applied a potent and well characterized soluble VEGF antagonist to adult C57Bl/6 mice post-SCI to elucidate the relative contribution of VEGF on the acute evolving microvascular response and its impact on functional recovery. While the VEGF Trap did not alter vascular density in the injury epicenter or penumbra, an overall increase in the number of Griffonia simplicifolia isolectin-B4 bound microvessels was observed, suggesting a VEGFdependency to more subtle aspects of endothelial plasticity post-SCI. Neutralizing endogenous VEGF neither attenuated nor exacerbated chronic histopathology or functional recovery. These results support the idea that overall, endogenous VEGF is not neuroprotective or detrimental following traumatic SCI. Furthermore, they suggest that angiogenesis in traumatically injured spinal tissue is regulated by multiple effectors and is not limited by endogenous VEGF activation of affected spinal microvessels.

Multiple sclerosis is an autoimmune disease characterized by multifocal areas of inflammation and demyelination within the central nervous system. The mechanism that triggers the disease remains elusive. However, recent findings may indicate that multiple sclerosis, at its source, could be a hemodynamic disorder. It has been found that multiple sclerosis patients exhibit significant stenoses in extracranial veins draining the central nervous system (in azygous and internal jugular veins), which are associated with significant pressure gradients measured across strictures. Such anatomic venous abnormalities were not found in the control group of healthy subjects. In this review, it is hypothesized that pathological refluxing venous flow in the cerebral and spinal veins increases the expression of adhesion molecules, particularly intercellular adhesion molecule-1 (ICAM-1), by the cerebrovascular endothelium. This, in turn, could lead to the increased permeability of the blood-brain barrier. Inflamed and activated endothelium could secrete proinflammatory cytokines, including GM-CSF and TGF-beta. In these settings, monocytes could transform into antigenpresenting cells and initiate an autoimmune attack against myelin-containing cells. Consequently, a potential therapeutic option for multiple sclerosis could be pharmacotherapy with either substances that strengthen the tight-junctions barrier, or with agents that reduce the expression of adhesion molecules. In addition, surgical correction could be an option in some anatomical variants of pathologic venous outflow. We are optimistic that a hemodynamic approach to the multiple sclerosis pathogenesis can open a new chapter of investigations and treatment of this debilitating neurologic disease.