Noninvasively differentiating acute and chronic nephropathies via multiparametric urea-CEST, nuclear Overhauser enhancement-CEST, and quantitative magnetization transfer MRI.

PURPOSE: Standardized blood tests often lack adequate sensitivity and specificity to capture the gradual progression of renal injuries. We suggest a multiparametric molecular MRI approach as a noninvasive tool for monitoring renal function loss and distinguishing different types of renal injuries. METHODS: CEST and quantitative magnetization transfer (qMT) imaging were performed on cisplatin (n = 16) and aristolochic acid (AA)-induced nephropathy (n = 22) mouse models at 7T with an infusion of either saline or urea. Seven-pool Lorentzian fitting was applied for the analysis of CEST Z-spectra, and the T1 -corrected CEST contrast apparent exchange-dependent relaxation (AREX) from urea (+1 ppm) and two nuclear Overhauser enhancement (NOE) pools (-1.6 and -3.5 ppm) were measured. Similarly, qMT spectra were fitted into two-pool Ramani equation and the relative semi-solid macromolecular pool-size ratio was measured. Histology of mouse kidneys was performed to validate the MR findings. RESULTS: AA model showed disrupted spatial gradients of urea in the kidney and significantly decreased NOE CEST and qMT contrast. The cisplatin model showed slightly decreased qMT contrast only. The orrelation of MR parameters to histological features showed that NOE CEST and qMT imaging are sensitive to both acute and chronic injuries, whereas urea CEST shows a significant correlation only to acute injuries. CONCLUSION: These results indicate that our multiparametric approach allows comprehensive and totally noninvasive monitoring of renal function and histological changes for distinguishing different nephropathies.

Delayed urea differential enhancement CEST (dudeCEST)-MRI with T1 correction for monitoring renal urea handling.

PURPOSE: We demonstrate a method of delayed urea differential enhancement CEST for probing urea recycling action of the kidney using expanded multi-pool Lorentzian fitting and apparent exchange-dependent relaxation compensation. METHODS: T1 correction of urea CEST contrast by apparent exchange-dependent relaxation was tested in phantoms. Nine mice were scanned at 7 Tesla following intraperitoneal injection of 2M 150 µL urea, and later saline. T1 maps and Z-spectra were acquired before and 20 and 40 min postinjection. Z-spectra were fit to a 7-pool Lorentzian model for CEST quantification and compared to urea assay of kidney homogenate. Renal injury was induced by aristolochic acid in 7 mice, and the same scan protocol was performed. RESULTS: Apparent exchange-dependent relaxation corrected for variable T1 times in phantoms. Urea CEST contrast at +1 ppm increased significantly at both time points following urea injection in the inner medulla and papilla. When normalizing the postinjection urea CEST contrast to the corresponding baseline value, both urea and saline injection resulted in identical fold changes in urea CEST contrast. Urea assay of kidney homogenate showed a significant correlation to both apparent exchange-dependent relaxation (R2 = 0.4687, P = .0017) and non-T1 -corrected Lorentzian amplitudes (R2 = 0.4964, P = .0011). Renal injury resulted in increased T1 time in the cortex and reduced CEST contrast change upon urea and saline infusion. CONCLUSION: Delayed urea enhancement following infusion can provide insight into renal urea handling. In addition, changes in CEST contrast at 1.0 ppm following saline infusion may provide insight into renal function.

Noninvasive imaging of renal urea handling by CEST-MRI.

PURPOSE: Renal function is characterized by concentration of urea for removal in urine. We tested urea as a CEST-MRI contrast agent for measurement of the concentrating capacity of distinct renal anatomical regions. METHODS: The CEST contrast of urea was examined using phantoms with different concentrations and pH levels. Ten C57BL/6J mice were scanned twice at 7 T, once following intraperitoneal injection of 2M 150 µL urea and separately following an identical volume of saline. Kidneys were segmented into regions encompassing the cortex, outer medulla, and inner medulla and papilla to monitor spatially varying urea concentration. Z-spectra were acquired before and 20 minutes after injection, with dynamic scanning of urea handling performed in between via serial acquisition of CEST images acquired following saturation at +1 ppm. RESULTS: Phantom experiments revealed concentration and pH-dependent CEST contrast of urea that was both acid- and base-catalyzed. Z-spectra acquired before injection showed significantly higher CEST contrast in the inner medulla and papilla (2.3% ± 1.9%) compared with the cortex (0.15% ± 0.75%, P = .011) and outer medulla (0.12% ± 0.58%, P = .008). Urea infusion increased CEST contrast in the inner medulla and papilla by 2.1% ± 1.9% (absolute), whereas saline infusion decreased CEST contrast by -0.5% ± 2.0% (absolute, P = .028 versus urea). Dynamic scanning revealed that thermal drift and diuretic status are confounding factors. CONCLUSION: Urea CEST has a potential of monitoring renal function by capturing the spatially varying urea concentrating ability of the kidneys.

Direct Quantification of Intervertebral Disc Water Content Using MRI.

BACKGROUND: Water content is a key parameter for simulating tissue swelling and nutrient diffusion. Accurately measuring water content throughout the intervertebral disc (NP = nucleus pulposus; AF = annulus fibrosus) is important for developing patient-specific models. Water content is measured using destructive techniques, Quantitative MRI has been used to estimate water content and detect early degeneration, but it is dependent on scan parameters, concentration of free water molecules, and fiber architecture. PURPOSE: To directly measure disc-tissue water content using quantitative MRI and compare MRI-based measurements with biochemical assays, and to quantify changes in disc geometry due to compression. STUDY TYPE: Basic science, controlled. SPECIMEN: Twenty bone-disc-bone motion segments from skeletally mature bovines. FIELD STRENGTH/SEQUENCE: 7T/3D fast low angle shot (FLASH) pulse sequence and a T2 rapid imaging with refocused echoes (RARE) sequence. ASSESSMENT: Disc volumes, NP and AF volumetric water content, and T2 relaxation times were measured through MRI; NP and AF tissue gravimetric water content, mass density, and glycosaminoglycan content were measured through a biochemical assay. STATISTICAL TESTS: Correlations between MRI-based measurement and biochemical composition were evaluated using Pearson's linear regression. RESULTS: Mechanical dehydration resulted in a decrease in disc volume by up to 20% and a decrease in disc height by up to 35%. Direct water content measurements for the NP was achieved by normalizing MRI-based spin density by NP mass density (1.10 ± 0.03 g/cm3 ). However, the same approach underestimated water content in the AF by ~10%, which may be due to a higher concentration of collagen fibers and bound water molecules. DATA CONCLUSION: Spin density or spin density normalized by mass density to estimate NP and AF water content was more accurate than correlations between water content and relaxation times. Mechanical dehydration decreased disc volume and disc height, and increased maximum cross-sectional area. LEVEL OF EVIDENCE: TECHNICAL EFFICACY STAGE: J. Magn. Reson. Imaging 2020;52:1152-1162.

Mesenchymal stem cells attenuate MRI-identifiable injury, protect white matter, and improve long-term functional outcomes after neonatal focal stroke in rats.

Cell therapy has emerged as a potential treatment for many neurodegenerative diseases including stroke and neonatal ischemic brain injury. Delayed intranasal administration of mesenchymal stem cells (MSCs) after experimental hypoxia-ischemia and after a transient middle cerebral artery occlusion (tMCAO) in neonatal rats has shown improvement in long-term functional outcomes, but the effects of MSCs on white matter injury (WMI) are insufficiently understood. In this study we used longitudinal T2-weighted (T2W) and diffusion tensor magnetic resonance imaging (MRI) to characterize chronic injury after tMCAO induced in postnatal day 10 (P10) rats and examined the effects of delayed MSC administration on WMI, axonal coverage, and long-term somatosensory function. We show unilateral injury- and region-dependent changes in diffusion fraction anisotropy 1 and 2 weeks after tMCAO that correspond to accumulation of degraded myelin basic protein, astrocytosis, and decreased axonal coverage. With the use of stringent T2W-based injury criteria at 72 hr after tMCAO to randomize neonatal rats to receive intranasal MSCs or vehicle, we show that a single MSC administration attenuates WMI and enhances somatosensory function 28 days after stroke. A positive correlation was found between MSC-enhanced white matter integrity and functional performance in injured neonatal rats. Collectively, these data indicate that the damage induced by tMCAO progresses over time and is halted by administration of MSCs. © 2016 Wiley Periodicals, Inc.

Ultralow-field and spin-locking relaxation dispersion in postmortem pig brain.

PURPOSE: To investigate tissue-specific differences, a quantitative comparison was made between relaxation dispersion in postmortem pig brain measured at ultralow fields (ULF) and spin locking at 7 tesla (T). The goal was to determine whether ULF-MRI has potential advantages for in vivo human brain imaging. METHODS: Separate specimens of gray matter and white matter were investigated using an ULF-MRI system with superconducting quantum interference device (SQUID) signal detection to measure T1ULF at fields from 58.7 to 235.0 µT and using a commercial MRI scanner to measure T1ρ7T at spin-locking fields from 5.0 to 235.0 µT. RESULTS: At matched field strengths, T1ρ7T is 50 to 100% longer than T1ULF. Furthermore, dispersion in T1ULF is close to linear between 58.7 and 235 µT, whereas dispersion in T1ρ7T is highly nonlinear over the same range. A subtle elbow in the T1ULF dispersion at approximately 140 µT is tentatively attributed to the local dipolar field of macromolecules. It is suggested that different relaxation mechanisms dominate each method and that ULF-MRI has a fundamentally different sensitivity to the macromolecular structure of neural tissue. CONCLUSIONS: Ultralow-field MRI may offer distinct, quantitative advantages for human brain imaging, while simultaneously avoiding the severe heating limitation imposed on high-field spin locking. Magn Reson Med 78:2342-2351, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Blood-brain barrier permeability is increased after acute adult stroke but not neonatal stroke in the rat.

The immaturity of the CNS at birth greatly affects injury after stroke but the contribution of the blood-brain barrier (BBB) to the differential response to stroke in adults and neonates is poorly understood. We asked whether the structure and function of the BBB is disrupted differently in neonatal and adult rats by transient middle cerebral artery occlusion. In adult rats, albumin leakage into injured regions was markedly increased during 2-24 h reperfusion but leakage remained low in the neonates. Functional assays employing intravascular tracers in the neonates showed that BBB permeability to both large (70 kDa dextran) and small (3 kDa dextran), gadolinium (III)-diethyltriaminepentaacetic acid tracers remained largely undisturbed 24 h after reperfusion. The profoundly different functional integrity of the BBB was associated with the largely nonoverlapping patterns of regulated genes in endothelial cells purified from injured and uninjured adult and neonatal brain at 24 h (endothelial transcriptome, 31,042 total probe sets). Within significantly regulated 1266 probe sets in injured adults and 361 probe sets in neonates, changes in the gene expression of the basal lamina components, adhesion molecules, the tight junction protein occludin, and matrix metalloproteinase-9 were among the key differences. The protein expression of collagen-IV, laminin, claudin-5, occludin, and zonula occludens protein 1 was also better preserved in neonatal rats. Neutrophil infiltration remained low in acutely injured neonates but neutralization of cytokine-induced neutrophil chemoattractant-1 in the systemic circulation enhanced neutrophil infiltration, BBB permeability, and injury. The markedly more integrant BBB in neonatal brain than in adult brain after acute stroke may have major implications for the treatment of neonatal stroke.

Erythropoietin increases neurogenesis and oligodendrogliosis of subventricular zone precursor cells after neonatal stroke.

BACKGROUND AND PURPOSE: Stroke is a common cause of neonatal brain injury. The subventricular zone is a lifelong source of newly generated cells in rodents, and erythropoietin (EPO) treatment has shown benefit in different animal models of brain injury. The purpose of this study is to investigate the specific role of exogenous EPO on subventricular zone progenitor cell populations in response to neonatal stroke. METHODS: Intraventricular injections of green fluorescent protein (GFP)-expressing lentivirus to label subventricular zone precursor cells were made in postnatal day 1 (P1) Long-Evans rats, which then underwent transient middle cerebral artery occlusion on P7. Middle cerebral artery occlusion and sham rats were treated with either vehicle or EPO (1000 U/kg) at reperfusion, 24 hours, and 7 days later. The density of double-labeled DCx+/GFP+, NeuN+/GFP+, O4+/GFP+, GFAP+/GFP+, as well as single-labeled GFP+ and Ki67+ cells, was calculated to determine cell fate outcome in the striatum at 72 hours and 2 weeks after stroke. RESULTS: There was a significant increase in DCx+/GFP+ and NeuN+/GFP+ neurons and O4+/GFP+ oligodendrocyte precursors, with decreased GFAP+/GFP+ astrocytes at both time points in EPO-middle cerebral artery occlusion animals. There was also a significant increase in GFP+ cells and Ki67+ proliferating cells in EPO compared with vehicle-middle cerebral artery occlusion animals. CONCLUSIONS: These data suggest that subventricular zone neural progenitor cells proliferate and migrate to the site of injury after neonatal stroke and multiple doses of EPO, with a shift in cell fate toward neurogenesis and oligodendrogliosis at both early and late time points. The contribution of local cell proliferation and neurogenesis remains to be determined.

Genetic deletion of CD36 enhances injury after acute neonatal stroke.

OBJECTIVE: The scavenger receptor CD36 is injurious in acute experimental focal stroke and neurodegenerative diseases in the adult. We investigated the effects of genetic deletion of CD36 (CD36ko) on acute injury, and oxidative and inflammatory signaling after neonatal stroke. METHODS: Postnatal day 9 CD36ko and wild-type (WT) mice were subjected to a transient middle cerebral artery occlusion (MCAO). Injury, phagocytosis of dying cells, and CD36 inflammatory signaling were determined. RESULTS: While the volume of tissue at risk by diffusion-weighted magnetic resonance imaging during MCAO was similar in neonatal CD36ko and WT mice, by 24 hours after reperfusion, injury was more severe in CD36ko and was associated with increased caspase-3 cleavage and reduced engulfment of neurons expressing cleaved caspase-3 by activated microglia. No significant superoxide generation was observed in activated microglia in injured WT, whereas increased superoxide production in vessels and nuclear factor (NF)-κB activation induced by MCAO were unaffected by lack of CD36. Lyn expression was higher in injured CD36ko, and cell type-specific patterns of Lyn expression were altered; Lyn was expressed in endothelial cells and microglia in WT but predominantly in dying neurons in CD36ko. INTERPRETATION: Lack of CD36 results in poorer short-term outcome from neonatal focal stroke due to lack of attenuation of NF-κB-mediated inflammation and diminished removal of apoptotic neuronal debris. Although inhibition of CD36 does not seem to be a good therapeutic target for protection after acute neonatal stroke, as it is after adult stroke, seeking better understanding of CD36 signaling in particular cell populations may reveal important therapeutic targets for neonatal stroke.

Microglial cells contribute to endogenous brain defenses after acute neonatal focal stroke.

Macrophages are viewed as amplifiers of ischemic brain injury, but the origin of injury-producing macrophages is poorly defined. The role of resident brain macrophages-microglial cells-in stroke remains controversial. To determine whether microglial cells exert injurious effects after neonatal focal stroke, we selectively depleted these cells with intracerebral injection of liposome-encapsulated clodronate before transient middle cerebral artery occlusion in postnatal day 7 rats. Phagocytosis of apoptotic neurons by activated microglia was poor in animals with unmanipulated microglia, and depletion of these cells did not increase the number of apoptotic neurons. Lack of microglia increased the brain levels of several cytokines and chemokines already elevated by ischemia-reperfusion, and also increased the severity and volume of injury, suggesting that microglial cells contribute to endogenous protection during the subacute injury phase. Then, to determine whether accumulation of reactive oxygen species in microglia adversely affects phagocytosis of dying neurons and contributes to injury, we delivered reduced glutathione (GSH) into microglia, again using liposomes. Remarkably, pharmacologically increased intracellular GSH concentrations in microglia induced superoxide accumulation in lipid rafts in these cells, further increased the brain levels of macrophage chemoattractants, and exacerbated injury. Together, these data show that microglia are part of the endogenous defense mechanisms and that, while antioxidants can protect the injured neonatal brain, high levels of reducing equivalents in activated microglia, GSH, trigger superoxide production, favor the reorganization of lipids, amplify local inflammation and exacerbate injury.

Magnetic resonance imaging of ferumoxide-labeled mesenchymal stem cells in cartilage defects: in vitro and in vivo investigations.

The purpose of this study was to (1) compare three different techniques for ferumoxide labeling of mesenchymal stem cells (MSCs), (2) evaluate if ferumoxide labeling allows in vivo tracking of matrix-associated stem cell implants (MASIs) in an animal model, and (3) compare the magnetic resonance imaging (MRI) characteristics of ferumoxide-labeled viable and apoptotic MSCs. MSCs labeled with ferumoxide by simple incubation, protamine transfection, or Lipofectin transfection were evaluated with MRI and histopathology. Ferumoxide-labeled and unlabeled viable and apoptotic MSCs in osteochondral defects of rat knee joints were evaluated over 12 weeks with MRI. Signal to noise ratios (SNRs) of viable and apoptotic labeled MASIs were tested for significant differences using t-tests. A simple incubation labeling protocol demonstrated the best compromise between significant magnetic resonance signal effects and preserved cell viability and potential for immediate clinical translation. Labeled viable and apoptotic MASIs did not show significant differences in SNR. Labeled viable but not apoptotic MSCs demonstrated an increasing area of T2 signal loss over time, which correlated to stem cell proliferation at the transplantation site. Histopathology confirmed successful engraftment of viable MSCs. The engraftment of iron oxide-labeled MASIs by simple incubation can be monitored over several weeks with MRI. Viable and apoptotic MASIs can be distinguished via imaging signs of cell proliferation at the transplantation site.

Characterization of a diffuse intrinsic pontine glioma cell line: implications for future investigations and treatment.

Diffuse intrinsic pontine gliomas arise almost exclusively in children, and despite advances in treatment, the majority of patients die within 2 years after initial diagnosis. Because of their infiltrative nature and anatomic location in an eloquent area of the brain, most pontine gliomas are treated without a surgical biopsy. The corresponding lack of tissue samples has resulted in a limited understanding of the underlying genetic and molecular biologic abnormalities associated with pontine gliomas, and is a substantial obstacle for the preclinical testing of targeted therapeutic agents for these tumors. We have established a human glioma cell line that originated from surgical biopsy performed on a patient with a pontine glioma. To insure sustainable in vitro propagation, tumor cells were modified with hTERT (human telomerase ribonucleoprotein reverse transcriptase), and with a luciferase reporter to enable non-invasive bioluminescence imaging. The hTERT modified cells are tumorigenic in athymic rodents, and produce brainstem tumors that recapitulate the infiltrative growth of brainstem gliomas in patients.

Neonatal cerebral hypoxia-ischemia impairs plasticity in rat visual cortex.

Ocular dominance plasticity (ODP) following monocular deprivation (MD) is a model of activity-dependent neural plasticity that is restricted to an early critical period regulated by maturation of inhibition. Unique developmental plasticity mechanisms may improve outcomes following early brain injury. Our objective was to determine the effects of neonatal cerebral hypoxia-ischemia (HI) on ODP. The rationale extends from observations that neonatal HI results in death of subplate neurons, a transient population known to influence development of inhibition. In rodents subjected to neonatal HI and controls, maps of visual response were derived from optical imaging during the critical period for ODP and changes in the balance of eye-specific response following MD were measured. In controls, MD results in a shift of the ocular dominance index (ODI) from a baseline of 0.15 to -0.10 (p < 0.001). Neonatal HI with moderate cortical injury impairs this shift, ODI = 0.14 (p < 0.01). Plasticity was intact in animals with mild injury and in those exposed to hypoxia alone. Neonatal HI resulted in decreased parvalbumin expression in hemispheres receiving HI compared with hypoxia alone: 23.4 versus 35.0 cells/high-power field (p = 0.01), with no change in other markers of inhibitory or excitatory neurons. Despite abnormal inhibitory neuron phenotype, spontaneous activity of single units and development of orientation selective responses were intact following neonatal HI, while overall visual responses were reduced. Our data suggest that specific plasticity mechanisms are impaired following early brain injury and that the impairment is associated with altered inhibitory neuronal development and cortical activation.

Validation of in vivo magnetic resonance imaging blood-brain barrier permeability measurements by comparison with gold standard histology.

BACKGROUND AND PURPOSE: We sought to validate the blood-brain barrier permeability measurements extracted from perfusion-weighted MRI through a relatively simple and frequently applied model, the Patlak model, by comparison with gold standard histology in a rat model of ischemic stroke. METHODS: Eleven spontaneously hypertensive rats and 11 Wistar rats with unilateral 2-hour filament occlusion of the right middle cerebral artery underwent imaging during occlusion at 4 hours and 24 hours after reperfusion. Blood-brain barrier permeability was imaged by gradient echo imaging after the first pass of the contrast agent bolus and quantified by a Patlak analysis. Blood-brain barrier permeability was shown on histology by the extravasation of Evans blue on fluorescence microscopy sections matching location and orientation of MR images. Cresyl-violet staining was used to detect and characterize hemorrhage. Landmark-based elastic image registration allowed a region-by-region comparison of permeability imaging at 24 hours with Evans blue extravasation and hemorrhage as detected on histological slides obtained immediately after the 24-hour image set. RESULTS: Permeability values in the nonischemic tissue (marginal mean ± SE: 0.15 ± 0.019 mL/min 100 g) were significantly lower compared to all permeability values in regions of Evans blue extravasation or hemorrhage. Permeability values in regions of weak Evans blue extravasation (0.23 ± 0.016 mL/min 100 g) were significantly lower compared to permeability values of in regions of strong Evans blue extravasation (0.29 ± 0.020 mL/min 100 g) and macroscopic hemorrhage (0.35 ± 0.049 mL/min 100 g). Permeability values in regions of microscopic hemorrhage (0.26 ± 0.024 mL/min 100 g) only differed significantly from values in regions of nonischemic tissue (0.15 ± 0.019 mL/min 100 g). CONCLUSIONS: Areas of increased permeability measured in vivo by imaging coincide with blood-brain barrier disruption and hemorrhage observed on gold standard histology.

Quantitative tissue oxygen measurement in multiple organs using 19F MRI in a rat model.

Measurement of individual organ tissue oxygen levels can provide information to help evaluate and optimize medical interventions in many areas including wound healing, resuscitation strategies, and cancer therapeutics. Echo planar (19) F MRI has previously focused on tumor oxygen measurement at low oxygen levels (pO(2)) <30 mmHg. It uses the linear relationship between spin-lattice relaxation rate (R(1)) of hexafluorobenzene (HFB) and pO(2). The feasibility of this technique for a wider range of pO(2) values and individual organ tissue pO(2) measurement was investigated in a rat model. Spin-lattice relaxation times (T(1) = 1/R(1)) of hexafluorobenzene were measured using (19) F saturation recovery echo planar imaging. Initial in vitro studies validated the linear relationship between R(1) and pO(2) from 0 to 760 mmHg oxygen partial pressure at 25, 37, and 41°C at 7 Tesla for hexafluorobenzene. In vivo experiments measured rat tissue oxygen (ptO2) levels of brain, kidney, liver, gut, muscle, and skin during inhalation of both 30 and 100% oxygen. All organ ptO(2) values significantly increased with hyperoxia (P < 0.001). This study demonstrates that (19) F MRI of hexafluorobenzene offers a feasible tool to measure regional ptO2 in vivo, and that hyperoxia significantly increases ptO2 of multiple organs in a rat model.

Optical sensor for diverse organic vapors at ppm concentration ranges.

A broadly responsive optical organic vapor sensor is described that responds to low concentrations of organic vapors without significant interference from water vapor. Responses to several classes of organic vapors are highlighted, and trends within classes are presented. The relationship between molecular properties (vapor pressure, boiling point, polarizability, and refractive index) and sensor response are discussed.

Accelerated multi-target chemical exchange saturation transfer magnetic resonance imaging of the mouse heart.

Cardiac chemical exchange saturation transfer-magnetic resonance imaging (CEST-MRI) has been used to probe levels of various metabolites that provide insight into myocardial structure and function. However, imaging of the heart using CEST-MRI is prolonged by the need to repeatedly acquire multiple images for a full Z-spectrum and to perform saturation and acquisition around cardiac and respiratory cycles. Compressed sensing (CS) reconstruction of sparse data enables accelerated acquisition, but reconstruction artifacts may bias subsequently derived measures of CEST contrast. In this study, we examine the impact of CS reconstruction of increasingly under-sampled cardiac CEST-MRI data on subsequent CEST contrasts of amine-containing metabolites and amide-containing proteins. Cardiac CEST-MRI data sets were acquired in six mice using low and high RF saturation for single and dual contrast generation, respectively. CEST-weighted images were reconstructed using CS methods at 2-5× levels of under-sampling. CEST contrasts were derived from corresponding Z-spectra and the impact of accelerated imaging on accuracy was assessed via analysis of variance. CS reconstruction preserved myocardial signal to noise ratio as compared to conventional reconstruction. However, greater absolute error and distribution of derived contrasts was observed with increasing acceleration factors. The results from this study indicate that acquisition of radial cardiac CEST-MRI data can be modestly, but meaningfully, accelerated via CS reconstructions with little error in CEST contrast quantification.

Vascular endothelial growth factor receptor-2 inhibition promotes cell death and limits endothelial cell proliferation in a neonatal rodent model of stroke.

BACKGROUND AND PURPOSE: Recent studies in neonatal rodent stroke models suggest that recovery is due in part to upregulation of hypoxia-inducible factor-1-a and its downstream target, vascular endothelial growth factor. Vascular endothelial growth factor is upregulated after a hypoxic insult and is involved in neuronal survival, angiogenesis, and neurogenesis during the recovery process. METHODS: We performed a 1.5-hour transient middle cerebral artery occlusion in 10-day-old rats with injury verified by diffusion-weighted MRI during occlusion to determine the effects of vascular endothelial growth factor receptor-2 (VEGFR2) inhibition on injury, apoptosis, and angiogenesis. Two days after reperfusion, the pups received either the VEGFR inhibitor, SU5416 (10 mg/kg per dose) or vehicle (1% dimethyl sulfoxide) for 3 days. RESULTS: VEGFR2 inhibition worsened injury 7 days after injury when compared with the vehicle-treated and injury-alone groups (P<0.01). Furthermore, receptor inhibition was associated with increased VEGFR2 expression 5 days after injury (P<0.05) and increased spectrin cleavage with a shift in favor of the calpain-mediated, caspase-3-independent cleavage (P<0.01). Increased areas of cleaved caspase-3 staining were seen in treated rats at 7 days (P<0.01) There were no differences in gliosis or macrophage recruitment as measured by glial fibrillary acidic protein and Iba-1 expression at this time point. Lastly, VEGFR2 inhibition did not affect the overall vessel surface area but reduced endothelial cell proliferation in injured caudate. CONCLUSIONS: Inhibition of VEGFR2 signaling worsens injury, affects cell death, and reduces endothelial cell proliferation after neonatal stroke. Injury exacerbation may be in part due to a shift of cell fate from apoptosis to necrosis on the continuum spectrum of cell death as well as effects on angiogenesis in the injured brain.

Altered fate of subventricular zone progenitor cells and reduced neurogenesis following neonatal stroke.

OBJECTIVE: To investigate the effects of neonatal stroke on progenitor cells lining the lateral ventricles. METHODS: Intraventricular injection of replication-incompetent green fluorescent protein (GFP)-expressing lentivirus was performed in postnatal day 1 (P1) rats to specifically label radial glia/type B neural stem cells and ependymal cells of the lateral ventricle. A subset of animals was exposed to transient middle cerebral artery occlusion (MCAO) at P7, with mild or moderate injury confirmed by diffusion-weighted MRI and histology. Newborn cells were identified by GFP expression, location and expression of cell type-specific markers in the striatum, cortex and olfactory bulb using confocal microscopy and systematic random sampling. RESULTS: Three weeks lentiviral GFP transduction of cells in the lateral ventricle, abundant GFP-expressing neurons and glia were identified in the rostral migratory stream, olfactory bulb and striatum as expected from labeling the subventricular zone (SVZ) type B neural stem cell lineage. Two weeks following mild or severe focal stroke at P7, no GFP-expressing neurons were detected in striatum or cortex although some single-labeled doublecortin+ immature neurons were detected in the penumbra. The densities of GFP+/ glial fibrillary acidic protein (GFAP)+ astrocytes and GFP+/O4+ oligodendrocytes were reduced in the striatum following MCAO (4.8 +/- 1.02 vs. 2.5 +/- 0.4 cells/high-power field, HPF; p = 0.005; 2.8+/- 1 vs. 0.5 +/- 0.2 cells/HPF, p = 0.008). Furthermore, there was a reduction of GFP+ cells in the olfactory bulb following MCAO (58.8 +/- 14.9 vs. 19.6 +/- 5.4 cells/HPF, p = 0.025). Finally, there was an increased percentage of GFP+/GFAP+ cells (70 vs. 50%), with a decreased proportion of GFP+/O4+ cells (14 vs. 30%) in injured animals. CONCLUSION: Neurogenesis originating from cells of the lateral ventricle, including SVZ type B cells, is significantly reduced following neonatal stroke. Furthermore, neonatal stroke disrupts gliogenesis in the striatum, decreasing overall numbers of new glia and shifting the population towards astrocytes.

Glutathione peroxidase activity modulates recovery in the injured immature brain.

OBJECTIVE: Mice subjected to traumatic brain injury at postnatal day 21 show emerging cognitive deficits that coincide with hippocampal neuronal loss. Here we consider glutathione peroxidase (GPx) activity as a determinant of recovery in the injured immature brain. METHODS: Wild-type and transgenic (GPxTg) mice overexpressing GPx were subjected to traumatic brain injury or sham surgery at postnatal day 21. Animals were killed acutely (3 or 24 hours after injury) to assess oxidative stress and cell injury in the hippocampus or 4 months after injury after behavioral assessments. RESULTS: In the acutely injured brains, a reduction in oxidative stress markers including nitrotyrosine was seen in the injured GPxTg group relative to wild-type control mice. In contrast, cell injury, with marked vulnerability in the dentate gyrus, was apparent despite no differences between genotypes. Magnetic resonance imaging demonstrated an emerging cortical lesion during brain maturation that was also indistinguishable between injured genotypes. Stereological analyses of cortical volumes likewise confirmed no genotypic differences between injured groups. However, behavioral tests beginning 3 months after injury demonstrated improved spatial memory learning in the GPxTg group. Moreover, stereological analysis within hippocampal subregions demonstrated a significantly greater number of neurons within the dentate of the GPx group. INTERPRETATION: Our results implicate GPx in recovery of spatial memory after traumatic brain injury. This recovery may be attributed, in part, to a reduction in early oxidative stress and selective, long-term sparing of neurons in the dentate.