FLASHForward: plasma wakefield accelerator science for high-average-power applications.

The FLASHForward experimental facility is a high-performance test-bed for precision plasma wakefield research, aiming to accelerate high-quality electron beams to GeV-levels in a few centimetres of ionized gas. The plasma is created by ionizing gas in a gas cell either by a high-voltage discharge or a high-intensity laser pulse. The electrons to be accelerated will either be injected internally from the plasma background or externally from the FLASH superconducting RF front end. In both cases, the wakefield will be driven by electron beams provided by the FLASH gun and linac modules operating with a 10 Hz macro-pulse structure, generating 1.25 GeV, 1 nC electron bunches at up to 3 MHz micro-pulse repetition rates. At full capacity, this FLASH bunch-train structure corresponds to 30 kW of average power, orders of magnitude higher than drivers available to other state-of-the-art LWFA and PWFA experiments. This high-power functionality means FLASHForward is the only plasma wakefield facility in the world with the immediate capability to develop, explore and benchmark high-average-power plasma wakefield research essential for next-generation facilities. The operational parameters and technical highlights of the experiment are discussed, as well as the scientific goals and high-average-power outlook. This article is part of the Theo Murphy meeting issue 'Directions in particle beam-driven plasma wakefield acceleration'.

Serological evidence for the co-circulation of two lineages of influenza D viruses in equine populations of the Midwest United States.

Influenza D virus (IDV) is a newly described influenza type of the Orthomyxoviridae virus family that was first isolated from diseased swine in 2011 and has subsequently been detected in cattle around the world in 2014. In addition, serological evidence for IDV infection in humans has been recently established. Despite all the progress, the full range of susceptible hosts for this novel virus has yet to be determined, but includes swine, bovine, small ruminants and human. This study was designed to determine if equine is a possible host to this newly emerging influenza virus. Three hundred and sixty-four equine serum samples were collected in 2015 from 141 farms within the Midwestern United States. Serum samples were examined using hemagglutination inhibition (HI) assay against two established IDV lineages (D/OK and D/660) and one IDV-related human ICV lineage (C/JHB). Results of this study showed 44 (44 of 364, 12%) samples positive for antibodies against D/OK, 39 (39 of 364, 11%) samples positive for antibodies against D/660, and 41 (41 of 364, 11%) samples positive for antibodies against C/JHB. A subset of these samples was further confirmed via microtitre neutralization (MN) assay. Our data demonstrated that horses are susceptible to two lineages of IDV, and that these viruses were present in equine populations throughout multiple Midwestern states of the United States. These findings continue to support the need for further surveillance of IDV viruses in agricultural species to work towards a better understanding of the full host range and natural reservoirs of influenza D virus.

Effect of differential rearing environments on nicotine-stimulated locomotor activity and nicotinic acetylcholine receptor subtypes / 中国药理学与毒理学杂志

OBJECTIVE Individuals vary in sensitivity to the behavioral effects of nicotine, resulting in differences in their vulnerability to addiction. The role of rearing environment in determining individual sensitivity to nicotine is unclear. The neuropharmacological mechanisms mediating the effect of rearing environment on the actions of nicotine are also understood. Thus, the contribution of rearing environment in determining the sensitivity to the locomotor effects of nicotine and regulating α4β2*- and α7-nicotinic acetylcholine (nACh) receptor expressionwas determined in rats reared in isolated (IC) or enriched (EC) conditions. METHODS To measure locomotor activity, adolescent rats (postnatal day 21- 51) were injected with saline (1 mL·kg-1) or nicotine (0.3 mg·kg-1) subcutaneously, then placed in chamber?swhere ambulatory activity was monitored for 30-min by computer for 14 daily sessions. α4β2*- andα7- nACh receptor expression in the mesolimbic dopamine pathway was determined by quantitative autoradiography of [125I]-epibatidine and [125I]-bungarotoxinbinding, respectively, in 16 μmol·L- 1 coronal sections. Values for receptor expression in fmol are x ± s of 8 brains and compared by two- tailed, unpaired t-test with P<0.05 considered significant. RESULTS EC-rats are similarly sensitive as IC-rats to the locomotor effects of nicotine. [125I]-epibatidine binding in the ventral tegmental area of EC-rats was reduced (2.8 ± 0.3 fmoL) compared to IC-rats (4.0 ± 0.4 fmoL); there was no difference in the nucleus accumbens. There was no difference between EC- and IC-rats in α7-nACh receptor expression in the mesolimbic dopamine pathway. CONCLUSION Rearing environment differentially regulates nACh receptor subtypes in EC and IC rats. These data suggest regulation of nACh receptors by environmental factors may be a mechanism for the protective effect of enrichment against altered sensi?tivity to nicotine in genetically vulnerable individuals. The characterization of these mechanisms will aid in development of novel pharmacological tools mimicking the protection afforded by environmental enrichment in nicotine-sensitive individuals.

Mental retardation and hypotonia seen in the knock out mouse for Canavan disease is not due to succinate semialdehyde dehydrogenase deficiency.

Canavan disease (CD) is an autosomal recessive disorder caused by aspartoacylase deficiency leading to accumulation of N-acetylaspartic acid and spongy degeneration of the brain. The mouse model for CD showed low levels of glutamate and gamma-aminobutyric acid (GABA) in the brain. Whether the low levels of glutamate and GABA observed in the CD mouse brain lead to abnormal production of glutamate-GABA associated enzymes and resulting succinate production is not obvious. While glutamate dehydrogenase and alpha-ketoglutarate dehydrogenase complex activities are lower in the cerebellum and brain stem of the CD mouse, alanine aminotransferase and succinate semialdehyde dehydrogenase (SSADH) activities and succinate level are similar to the levels observed in the wild type. Deficiency of SSADH has been suggested to be associated with mental retardation and hypotonia, similar to the clinical features of CD. The normal SSADH activity in the CD mouse brain suggests that mental retardation and hypotonia seen in the CD mouse is not due to SSADH activity and if documented also in patients with CD.

MR microscopy of cobalt-labeled nerve cells and pathways in an invertebrate brain (Sepia officinalis, Cephalopoda).

This article describes a novel application of contrast-enhanced MR microscopy to trace nerve cells and pathways through small invertebrate brains. Using the cuttlefish Sepia officinalis (Cephalopoda) as a model, the cells and pathways of one of the brain nerves were labeled with paramagnetic cobalt(II) ions by conventional centripetal cobalt iontophoresis. In MR microscopy, the cobalt-labeled cell bodies and pathways became hypointense in 9.4 T spin echo images. Their course and distribution were identical with those seen with conventional histological techniques after cobalt sulphide precipitation (with or without subsequent silver intensification). Magn Reson Med 45:575-579, 2001.

Absence of perilipin results in leanness and reverses obesity in Lepr(db/db) mice.

Obesity is a disorder of energy balance. Hormone-sensitive lipase (HSL) mediates the hydrolysis of triacylglycerol, the major form of stored energy in the body. Perilipin (encoded by the gene Plin), an adipocyte protein, has been postulated to modulate HSL activity. We show here that targeted disruption of Plin results in healthy mice that have constitutively activated fat-cell HSL. Plin -/- mice consume more food than control mice, but have normal body weight. They are much leaner and more muscular than controls, have 62% smaller white adipocytes, show elevated basal lipolysis that is resistant to beta-adrenergic agonist stimulation, and are cold-sensitive except when fed. They are also resistant to diet-induced obesity. Breeding the Plin -/- alleles into Leprdb/db mice reverses the obesity by ncreasing the metabolic rate of the mice. Our results demonstrate a role for perilipin in reining in basal HSL activity and regulating lipolysis and energy balance; thus, agents that inactivate perilipin may prove useful as anti-obesity medications.

Knock-out mouse for Canavan disease: a model for gene transfer to the central nervous system.

BACKGROUND: Canavan disease (CD) is an autosomal recessive leukodystrophy characterized by deficiency of aspartoacylase (ASPA) and increased levels of N-acetylaspartic acid (NAA) in brain and body fluids, severe mental retardation and early death. Gene therapy has been attempted in a number of children with CD. The lack of an animal model has been a limiting factor in developing vectors for the treatment of CD. This paper reports the successful creation of a knock-out mouse for Canavan disease that can be used for gene transfer. METHODS: Genomic library lambda knock-out shuttle (lambdaKOS) was screened and a specific pKOS/Aspa clone was isolated and used to create a plasmid with 10 base pair (bp) deletion of exon four of the murine aspa. Following linearization, the plasmid was electroporated to ES cells. Correctly targeted ES clones were identified following positive and negative selection and confirmed by Southern analysis. Chimeras were generated by injection of ES cells to blastocysts. Germ line transmission was achieved by the birth of heterozygous mice as confirmed by Southern analysis. RESULTS: Heterozygous mice born following these experiments have no overt phenotype. The homozygous mice display neurological impairment, macrocephaly, generalized white matter disease, deficient ASPA activity and high levels of NAA in urine. Magnetic resonance imaging (MRI) and spectroscopy (MRS) of the brain of the homozygous mice show white matter changes characteristic of Canavan disease and elevated NAA levels. CONCLUSION: The newly created ASPA deficient mouse establishes an important animal model of Canavan disease. This model should be useful for developing gene transfer vectors to treat Canavan disease. Vectors for the central nervous system (CNS) and modulation of NAA levels in the brain should further add to the understanding of the pathophysiology of Canavan disease. Data generated from this animal model will be useful for developing strategies for gene therapy in other neurodegenerative diseases.

Effect of a neuronal sodium channel blocker on magnetic resonance derived indices of brain water content during global cerebral ischemia.

Diffusion-weighted magnetic resonance imaging (DWI) with calculation of the apparent diffusion coefficient (ADC) of water is a widely used noninvasive method to measure movement of water from the extracellular to the intracellular compartment during cerebral ischemia. Lamotrigine, a neuronal Na(+) channel blocker, has been shown to attenuate the increase in extracellular concentrations of excitatory amino acids (EAA) during ischemia and to improve neurological and histological outcome. Because of its proven ability to reduce EAA levels during ischemia, lamotrigine should also minimize excitotoxic-induced increases in intracellular water content and therefore attenuate changes in the ADC. In this study, we sought to determine the effect of lamotrigine on intra- and extracellular water shifts during transient global cerebral ischemia. Fifteen New Zealand white rabbits were anesthetized and randomized to one of three groups: a control group, a lamotrigine-treated group, or a sham group. After being positioned in the bore of the magnet, a 12-min 50-s period of global cerebral ischemia was induced by inflating a neck tourniquet. During ischemia and early reperfusion there was a similar and significant decrease of the ADC in both the lamotrigine and control group. The ADC in the sham ischemia group remained at baseline throughout the experiment. Lamotrigine-mediated blockade of voltage-gated sodium channels did not prevent the intracellular movement of water during 12 min 50 s of global ischemia, as measured by the ADC, suggesting that the ADC decline may not be mediated by voltage-gated sodium influx and glutamate release.

Development of a human to murine orthotopic xenotransplanted lung cancer model.

The goal was to develop a clinically relevant animal model that could be used to assess the efficacy of therapeutic interventions in lung cancer. Two cell lines, noncancerous control (BEAS2-B, immortalized human bronchial-epithelial cell line) and cancerous (BZR-T33, H-ras transformed BEAS2-B) were implanted into nude (athymic) mice. Two groups (n = 10 each) received dorsoscapular subcutaneous injection of 10(6) cells from either cell line. BEAS2-B cells were nontumorigenic, whereas mice with BZR-T33 cells had tumors (9,510 +/- 4,307 mm3) confirmed by histology, and a significantly smaller body weight (BZR-T33, 28.5 +/- 0.49 vs. BEAS2-B, 30.7 +/- 0.75 g, p < .05). The next phase evaluated invasion/metastasis. Two groups (n = 10 each) received 10(6) cells from either cell line injected into tail veins. Animals receiving BZR-T33 cells had a smaller body weight, palpable lung masses (67%), obvious tail masses (44%), and average tumor burden (1,120 +/- 115 mm3), and histology revealed invasion of lung tissue and interstitial hemorrhage. In development of the orthotopic xenotransplanted model, mice (2 groups, n = 10 each) received 10(6) cells from either cell line implanted into the lungs through a tracheotomy. Animals with BZR-T33 cells did not survive past 59 days and had a smaller body weight, increased lung weight, lung masses (100%), and metastatic loci (30%). Magnetic resonance imaging (MRI) confirmed the presence of masses in intubated live mice, later confirmed by histology. In summary, the H-ras transfected cell line developed lung masses following tail-vein injection and endotracheal seeding. Evaluation by MRI allows for a comprehensive model with significant potential in the study of lung cancer.

A visceral pain pathway in the dorsal column of the spinal cord.

A limited midline myelotomy at T10 can relieve pelvic cancer pain in patients. This observation is explainable in light of strong evidence in support of the existence of a visceral pain pathway that ascends in the dorsal column (DC) of the spinal cord. In rats and monkeys, responses of neurons in the ventral posterolateral thalamic nucleus to noxious colorectal distention are dramatically reduced after a lesion of the DC at T10, but not by interruption of the spinothalamic tract. Blockade of transmission of visceral nociceptive signals through the rat sacral cord by microdialysis administration of morphine or 6-cyano-7-nitroquinoxaline-2,3-dione shows that postsynaptic DC neurons in the sacral cord transmit visceral nociceptive signals to the gracile nucleus. Retrograde tracing studies in rats demonstrate a concentration of postsynaptic DC neurons in the central gray matter of the L6-S1 spinal segments, and anterograde tracing studies show that labeled axons ascend from this region to the gracile nucleus. A similar projection from the midthoracic spinal cord ends in the gracile and cuneate nuclei. Behavioral experiments demonstrate that DC lesions reduce the nocifensive responses produced by noxious stimulation of the pancreas and duodenum, as well as the electrophysiological responses of ventral posterolateral neurons to these stimuli. Repeated regional blood volume measurements were made in the thalamus and other brain structures in anesthetized monkeys in response to colorectal distention by functional MRI. Sham surgery did not reduce the regional blood volume changes, whereas the changes were eliminated by a DC lesion at T10.

Reversal of weightlessness-induced musculoskeletal losses with androgens: quantification by MRI.

Microgravity causes rapid decrement in musculoskeletal mass is associated with a marked decrease in circulatory testosterone levels, as we reported in hindlimb-suspended (HLS) rats. In this model which simulates microgravity, we hypothesized that testosterone supplementation should prevent these losses, and we tested this in two studies. Muscle volumes and bone masses were quantitated by using magnetic resonance imaging (MRI) on day 12. In the first study, 12-wk-old Sprague-Dawley rats that were HLS for 12 days lost 28.5% of muscle volume (53.3 +/- 4.8 vs. 74.5 +/- 3.6 cm3 in the ground control rats; P < 0.001) and had a 5% decrease in bone mineral density (BMD) (P < 0.05). In the second study, 30 male 12-wk-old Wistar rats were HLS and were administered either a vehicle (control), testosterone, or nandrolone decanoate (ND). An additional 20 rats were used as ground controls, one-half of which received testosterone. HLS rats had a significant reduction in muscle volume (42.9 +/- 3.0 vs. 56 +/- 1.8 cm3 in ground control rats; P < 0.01). Both testosterone and ND treatments prevented this muscle loss (51.5 +/- 2 and 51.6 +/- 1.2 cm3, respectively; a 63% improvement; P < 0. 05). There were no statistical differences between the two active treatment groups nor with the ground controls. Similarly, there was an 85% improvement in BMD in the testosterone group (1.15 +/- 0.04 vs. 1.04 +/- 0.04 density units in vehicle controls; P < 0.05) and a 76% improvement in the ND group (1.13 +/- 0.07 density units), whereas ground control rats had a BMD of 1.17 +/- 0.03 density units. Because serum testosterone levels are markedly reduced in this model of simulated microgravity, androgen replacement seems to be a rational countermeasure to prevent microgravity-induced musculoskeletal losses.

Effect of NGF treatment on outcome measures in a rat model of middle cerebral artery occlusion.

Ischemic insults to the brain result in a time-dependent increase in neuronal death that is responsible for some of the functional deficits associated with stroke. Our working hypothesis is that ischemia results in a prompt depletion of high energy phosphate species resulting in decreased pH and glutathione levels in brain in a temporal and spatial pattern that disrupts nerve growth factor homeostasis and increases neuronal apoptosis. Here we show hemispheric depletion of active phosphate species after ischemia. Also, we observed that the striatum is an early target for oxidative stress that is followed by energy metabolic impairment and altered neurotrophin levels that were detected by noninvasive magnetic resonance imaging (MRI) measurements of cytotoxicity and conventional biochemical determinations of apoptosis, glutathione, and nerve growth factor (NGF) protein levels in a pattern distinct from that observed in the hippocampus. Furthermore, early assessment of intracellular pH by 31P-magnetic resonance spectroscopy (31P-MRS) was a predictor of later infarct development as determined by MRI. We also show that pretreatment with pharmacological doses of NGF did not have overall significant beneficial consequences on irreversible ischemia in an intraluminal unilateral irreversible model of stroke in rat brain.

Effect of nitric oxide synthase inhibitor on a hyperglycemic rat model of reversible focal ischemia: detection of excitatory amino acids release and hydroxyl radical formation.

The purpose of this study was to investigate the mechanisms by which a nitric oxide synthase (NOS) inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), is neuroprotective in the hyperglycemic rat model of 2 h of transient middle cerebral artery occlusion followed by 2 h of reperfusion (MCAO/R). The salicylate trapping method was used in conjunction with a microdialysis technique to continuously estimate hydroxyl radical (.OH) formation by measurement of the stable adducts 2,3- and 2,5-dihydroxybenzoic acid (DHBA). Extracellular excitatory amino acids (EAAs) were detected from the same microdialysis samples. Magnetic resonance imaging (MRI) techniques were used to measure neuronal and cerebrovascular injury. The magnitude of EAA release correlated with the levels of the .OH adducts. Treatment with L-NAME (3 mg/kg, i.p.) 1 min before MCAO, and again 1 min before reperfusion, reduced the levels of DHBA by 46. 4% and glutamate by 50.5% in the hyperglycemic rats compared to untreated hyperglycemic controls. MRI indicated that L-NAME reduced the no-reflow zone and the cytotoxic lesion volume to 22.5% and 21. 0%, respectively, that of hyperglycemic controls. Co-treatment with the nitric oxide (NO) donor L-arginine completely eliminated the protective effects of l-NAME with respect to .OH and EAA levels as well as MRI lesion volume. Our data suggest that hyperglycemic MCAO/R results in excessive glutamate excitotoxicity, leading to enhanced generation of .OH via a NO-mediated mechanism, in turn resulting in severe ischemia/reperfusion brain injury.

Serial determinations of cerebral water content by magnetic resonance imaging after an infusion of hypertonic saline.

OBJECTIVE: To determine regional cerebral water content in vivo by magnetic resonance imaging (MRI) after the administration of 7.5% saline in brain-lesioned rabbits. DESIGN: Randomized, controlled, intervention trial. SETTING: University animal laboratory. SUBJECTS: Eighteen male New Zealand white rabbits, randomly assigned to one of three groups. INTERVENTIONS: The animals were anesthetized (1% halothane), intubated, and mechanically ventilated to maintain end-tidal CO2 tension between 30 and 35 mm Hg (4 and 4.7 kPa). Arterial and central venous catheters were inserted and arterial blood samples were serially obtained during the experiment. Serum osmolality was measured. A cryogenic cerebral lesion was produced by pouring liquid nitrogen for 1 min into a funnel placed on the intact skull over the right hemisphere. One group of animals received 20 mL of 7.5% saline intravenously 150 mins after the cerebral lesion was generated (7.5% saline group, n = 7). A second group of animals received the same volume of 0.9% saline intravenously (0.9% saline group, n = 7). In a third group of animals (control group, n = 4) no lesion was created and no fluid administered. MEASUREMENTS AND MAIN RESULTS: Five spin-echo T2-weighted MRIs of the brain were acquired at 90 mins (Baseline 1), 120 mins (Baseline 2), 150 mins (Infusion), 180 mins (Infusion + 30 mins), and 210 mins (Infusion + 60 mins) after the generation of the cerebral lesion. In the control group, two scans separated by a time interval of 120 mins were performed. The percent changes in signal intensity between the first and the four following scans of a coronal slice of the central region were determined. Analysis of variance and the Mann-Whitney U test were used for statistical analysis. Data are presented as mean +/- SD; p < .05 was considered significant. Serum osmolality increased significantly from 308 +/- 13 mosm/L to 349 +/- 19 mosm/L after the infusion of 20 mL of 7.5% saline, but did not change after the administration of 0.9% saline. Signal intensity in the area between the caudal edge of the core of the lesion and the basal ganglia was 9 +/- 8% higher on the injured side than in the corresponding area on the contralateral side (p < .05). Compared with Baseline 1, signal intensity at Infusion + 60 mins decreased by 26.3 +/- 13.7% in the 7.5% saline group, whereas it decreased by 10.4 +/- 8.6% in the 0.9% saline group (p < .05 between groups). Signal intensity decreased only slightly and nonsignificantly by 0.6 +/- 4.4% between the two scans in the control group. CONCLUSIONS: The administration of a 7.5% saline solution causes a prompt and substantial decrease in cerebral water content as assessed by spin-echo T2-weighted MRI. Magnetic resonance imaging offers the opportunity for repeated, noninvasive in vivo determinations of cerebral water content.

APE/Ref-1 responses to ischemia in rat brain.

Cerebral ischemia and the aftermath of reperfusion form a hypoxic/hyperoxic sequence of events that can trigger oxidative stress response cascades in neurons of the central nervous system. After transient ischemia there is an increase in intracellular Ca2+ release, extracellular glutamate, reactive oxygen species (ROS) and nitric oxide, genotoxic events that stimulate DNA repair. Increased oxidative stress and interrupted blood flow in ischemia, like DNA repair, also deplete cellular ATP and commit neurons to apoptosis. We report that levels of the DNA repair enzyme apurinic/apyrimidinic endonuclease (APE/Ref-1) decreased significantly in the hippocampus but not other brain areas after 6 h of reperfusion following an induced ischemic insult. This specific inhibition of APE/Ref-1 expression may affect the extent of apoptosis after ischemia.

NG-nitro-L-arginine methyl ester modifies the input function measured by dynamic susceptibility contrast magnetic resonance imaging.

In rat brain dynamic susceptibility contrast magnetic resonance (MR) images, vessels visible on the same scan plane as the brain tissue were used to measure the characteristics of the input function of the MR contrast agent gadopentetate dimeglumine. MR images were acquired 30 and 60 minutes after intravenous injections of 3 mg/kg and 15 mg/kg NG-Nitro-L-arginine methyl ester (L-NAME) (n = 9). The time of arrival (TOA) and the mean transit time corrected for TOA of the input function were increased by 3 mg/kg or 15 mg/kg L-NAME. The area of the input function was increased by 15 mg/kg L-NAME. In two animals, similar modifications of the input function induced by 20 mg/kg L-NAME were reversed by infusion of sodium nitroprusside. In two other animals, MABP was increased by phenylephrine to a similar extent as in L-NAME experiments, but did not induce the same modifications of the input function, showing that the action of L-NAME on the input function was not simply caused by an effect on MABP. These results show that the input function can be significantly altered by manipulations widely used in cerebrovascular studies. These input function changes have important implications for calculation of cerebral blood flow.

Perfusion deficit parallels exacerbation of cerebral ischemia/reperfusion injury in hyperglycemic rats.

Magnetic resonance imaging (MRI) techniques were used to determine the effect of preexisting hyperglycemia on the extent of cerebral ischemia/reperfusion injury and the level of cerebral perfusion. Middle cerebral artery occlusion (MCAO) was induced by a suture insertion technique. Forty one rats were divided into hyperglycemic and normoglycemic groups with either 4 hours of continuous MCAO or 2 hours of MCAO followed by 2 hours of reperfusion. Diffusion-weighted imaging (DWI) was performed at 4 hours after MCAO to quantify the degree of injury in 6 brain regions. Relative cerebral blood flow (CBF) and cerebral blood volume (CBV) were estimated using gradient echo (GE) bolus tracking and steady-state spin echo (SE) imaging techniques, respectively. Brain injury correlated with the perfusion level measured in both SE CBV and dynamic GE CBF images. In the temporary MCAO model, mean lesion size in DWI was 118% larger and hemispheric CBV was reduced by 37% in hyperglycemic compared with normoglycemic rats. Hyperglycemia did not significantly exacerbate brain injury or CBV deficit in permanent MCAO models. We conclude that preexisting hyperglycemia increases acute postischemic MRI-measurable brain cellular injury in proportion to an associated increased microvascular ischemia.

Hydroxyl radical formation in hyperglycemic rats during middle cerebral artery occlusion/reperfusion.

Preexisting hyperglycemia is associated with enhanced reperfusion injury in the postischemic rat brain. The goal of this study was to evaluate whether the hyperglycemic exacerbation of brain injury is associated with enhanced generation of hydroxyl radicals in rats subjected to middle cerebral artery occlusion (2 h), followed by reperfusion (2 h). Magnetic resonance images revealed the exacerbation of focal brain injury in hyperglycemic rats. The salicylate trapping method was used in conjunction with microdialysis to continuously estimate hydroxyl radical production by measurement of the stable adducts 2,3- and 2,5-dihydroxybenzoic acid (DHBA) during ischemia/reperfusion. In normoglycemic rats, from a mean baseline level of 130 nmol/l, 2,3-DHBA levels surged to peak levels of 194 nmol/l 45 min into ischemia and to 197 nmol/l 15-30 min into the reperfusion period, returning to baseline by 2 h into reperfusion. A similar temporal profile was observed in hyperglycemic rats, except that absolute 2,3-DHBA levels were higher (165 nmol/l at baseline, 317 nmol/l peak during ischemia, 333 nmol/l peak during reperfusion), and levels remained significantly high (p < .05) throughout the reperfusion period. These results suggest that hydroxyl radical is an important contributor to the exacerbation of neuronal and cerebrovascular injury after focal ischemia/reperfusion in hyperglycemic rats.

A comparison of the early development of ischemic brain damage in normoglycemic and hyperglycemic rats using magnetic resonance imaging.

The early evolution of ischemic brain injury under normoglycemic and streptozotocin-induced hyperglycemic plasma conditions was studied using magnetic resonance imaging (MRI). Male Sprague-Dawley rats were subjected to either permanent middle cerebral artery occlusion (MCAO), or 1-h MCAO followed by reperfusion using the intraluminal suture insertion method. The animals were divided into four groups each with eight rats: normoglycemia with permanent MCAO, normoglycemia with 1-h MCAO, hyperglycemia with permanent MCAO, and hyperglycemia with 1-h MCAO. Diffusion-weighted images (DWIs) and T2-weighted images (T2WIs) were aquired every 1 h from 20 min until 6 h after MCAO, at which time cerebral plasma volume images (PVIs) were acquired. Tissue infarction was determined by triphenyltetrazolium chloride staining at 7 h after MCAO. The ischemic damage, measured as the area of DWI and T2WI hyperintensity and tissue infarction, increased significantly in hyperglycemic rats in both permanent and transient MCAO models. In the permanent MCAO model, the maximal apparent water diffusion coefficient (ADC) decline under either normo- or hyperglycemia was about 40%, but the speed of ADC drop was faster in hyperlgycemic rats than in normoglycemic rats. Reperfusion after 1 h of MCAO in normoglycemic rats partly reversed the decline in ADC, whereas the low ADC area continued to expand after reperfusion in the hyperglycemic group. Between the two hyperglycemic groups with either permanent MCAO or reperfusion, no significant difference was found in the infarct volume measured at 7 h after MCAO. However, reperfusion dramatically increased the extent and accelerated the development rate of vasogenic edema. ADC in the hyperglycemic reperfusion group also dropped to a lower level. A large "no-reflow" zone was found in the ischemic hemisphere in the hyperglycemic reperfusion group. This study provides strong evidence to support that preischemic hyperglycemia exacerbates ischemic damage in both transient and permanent MCAO models and demonstrates, using MRI, that reperfusion under preischemic hyperglycemia accelerates the evolution of early ischemic injury.