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PURPOSE: Direct assessment of myelin has the potential to reveal central nervous system abnormalities and serve as a means to follow patients with demyelinating disorders during treatment. Here, we investigated the feasibility of direct imaging and quantification of the myelin proton pool, without the many possible confounds inherent to indirect methods, via long-T2 suppressed 3D ultra-short echo-time (UTE) and zero echo-time (ZTE) MRI in ovine spinal cord. METHODS: ZTE and UTE experiments, with and without inversion-recovery (IR) preparation, were conducted in ovine spinal cords before and after D2O exchange of tissue water, on a 9.4T vertical-bore micro-imaging system, along with some feasibility experiments on a 3T whole-body scanner. Myelin density was quantified relative to reference samples containing various mass fractions of purified myelin lipid, extracted via the sucrose gradient extraction technique, and reconstituted by suspension in water, where they spontaneously self-assemble into an ensemble of multi-lamellar liposomes, analogous to native myelin. RESULTS: MR signal amplitudes from reference samples at 9.4T were linearly correlated with myelin concentration (R2 = 0.98-0.99), enabling their use in quantification of myelin fraction in neural tissues. An adiabatic inversion-recovery preparation was found to effectively suppress long-T2 water signal in white matter, leaving short-T2 myelin protons to be imaged. Estimated myelin lipid fractions in white matter were 19.9%-22.5% in the D2O-exchanged spinal cord, and 18.1%-23.5% in the non-exchanged spinal cord. Numerical simulations based on the myelin spectrum suggest that approximately 4.59% of the total myelin proton magnetization is observable by IR-ZTE at 3T due to T2 decay and the inability to excite the shortest T2* components. Approximately 380 µm of point-spread function blurring is predicted, and ZTE images of the spinal cord acquired at 3T were consistent with this estimate. CONCLUSION: In the present implementation, IR-UTE at 9.4T produced similar estimates of myelin concentration in D2O-exchanged and non-exchanged spinal cord white matter. 3T data suggest that direct myelin imaging is feasible, but remaining challenging on clinical MR systems.
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Procesamiento de Imagen Asistido por Computador/métodos , Imagen por Resonancia Magnética/métodos , Vaina de Mielina , Médula Espinal/diagnóstico por imagen , Animales , Lípidos/análisis , Protones , OvinosRESUMEN
Correct localization of epileptic foci can improve surgical outcome in patients with drug-resistant seizures. Our aim was to demonstrate that systemically injected nanoparticles identify activated immune cells, which have been reported to accumulate in epileptogenic brain tissue. Fluorescent and magnetite-labeled nanoparticles were injected intravenously to rats with lithium-pilocarpine-induced chronic epilepsy. Cerebral uptake was studied ex vivo by confocal microscopy and MRI. Cellular uptake and biological effects were characterized in vitro in murine monocytes and microglia cell lines. Microscopy confirmed that the nanoparticles selectively accumulate within myeloid cells in the hippocampus, in association with inflammation. The nanoparticle signal was also detectable by MRI. The in vitro studies demonstrate rapid nanoparticle uptake and good cellular tolerability. We show that nanoparticles can target myeloid cells in epileptogenic brain tissue. This system can contribute to pre-surgical and intra-surgical localization of epileptic foci, and assist in detecting immune system involvement in epilepsy.
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Encéfalo , Epilepsia/cirugía , Imagen por Resonancia Magnética/métodos , Nanopartículas de Magnetita , Animales , Hipocampo , Humanos , Inflamación , Ratones , Microscopía Confocal , RatasRESUMEN
Agmatine (AGM), a product of arginine decarboxylation, influences multiple physiologic and metabolic functions. However, the mechanism(s) of action, the impact on whole body gene expression and metabolic pathways, and the potential benefits and risks of long term AGM consumption are still a mystery. Here, we scrutinized the impact of AGM on whole body metabolic profiling and gene expression and assessed a plausible mechanism(s) of AGM action. Studies were performed in rats fed a high fat diet or standard chow. AGM was added to drinking water for 4 or 8 weeks. We used (13)C or (15)N tracers to assess metabolic reactions and fluxes and real time quantitative PCR to determine gene expression. The results demonstrate that AGM elevated the synthesis and tissue level of cAMP. Subsequently, AGM had a widespread impact on gene expression and metabolic profiling including (a) activation of peroxisomal proliferator-activated receptor-α and its coactivator, PGC1α, and (b) increased expression of peroxisomal proliferator-activated receptor-γ and genes regulating thermogenesis, gluconeogenesis, and carnitine biosynthesis and transport. The changes in gene expression were coupled with improved tissue and systemic levels of carnitine and short chain acylcarnitine, increased ß-oxidation but diminished incomplete fatty acid oxidation, decreased fat but increased protein mass, and increased hepatic ureagenesis and gluconeogenesis but decreased glycolysis. These metabolic changes were coupled with reduced weight gain and a curtailment of the hormonal and metabolic derangements associated with high fat diet-induced obesity. The findings suggest that AGM elevated the synthesis and levels of cAMP, thereby mimicking the effects of caloric restriction with respect to metabolic reprogramming.
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Agmatina/farmacología , AMP Cíclico/metabolismo , Ácidos Grasos/metabolismo , Gluconeogénesis/efectos de los fármacos , Hígado/metabolismo , Obesidad/tratamiento farmacológico , Agmatina/farmacocinética , Animales , Transporte Biológico Activo/efectos de los fármacos , Carnitina/análogos & derivados , Carnitina/metabolismo , Grasas de la Dieta/efectos adversos , Grasas de la Dieta/farmacología , Regulación de la Expresión Génica/efectos de los fármacos , Humanos , Masculino , Metaboloma , Obesidad/inducido químicamente , Obesidad/metabolismo , Oxidación-Reducción/efectos de los fármacos , PPAR gamma/biosíntesis , Coactivador 1-alfa del Receptor Activado por Proliferadores de Peroxisomas gamma , Ratas , Ratas Sprague-Dawley , Factores de Tiempo , Factores de Transcripción/biosíntesisRESUMEN
Osteoporosis involves the degradation of the bone's trabecular architecture, cortical thinning and enlargement of cortical pores. Increased cortical porosity is a major cause of the decreased strength of osteoporotic bone. The majority of cortical pores, however, are below the resolution limit of MRI. Recent work has shown that porosity can be evaluated by MRI-based quantification of bone water. Bi-exponential T2 * fitting and adiabatic inversion preparation are the two most common methods purported to distinguish bound and pore water in order to quantify matrix density and porosity. To assess the viability of T2 * bi-component analysis as a method for the quantification of bound and pore water fractions, we applied this method to human cortical bone at 1.5, 3, 7 and 9.4 T, and validated the resulting pool fractions against micro-computed tomography-derived porosity and gravimetrically determined bone densities. We also investigated alternative methods: two-dimensional T1 -T2 * bi-component fitting by incorporation of saturation recovery, one- and two-dimensional fitting of Carr-Purcell-Meiboom-Gill (CPMG) echo amplitudes, and deuterium inversion recovery. The short-T2 * pool fraction was moderately correlated with porosity (R(2) = 0.70) and matrix density (R(2) = 0.63) at 1.5 T, but the strengths of these associations were found to diminish rapidly as the field strength increased, falling below R(2) = 0.5 at 3 T. The addition of the T1 dimension to bi-component analysis only slightly improved the strengths of these correlations. T2 *-based bi-component analysis should therefore be used with caution. The performance of deuterium inversion recovery at 9.4 T was also poor (R(2) = 0.50 vs porosity and R(2) = 0.46 vs matrix density). The CPMG-derived short-T2 fraction at 9.4 T, however, was highly correlated with porosity (R(2) = 0.87) and matrix density (R(2) = 0.88), confirming the utility of this method for independent validation of bone water pools.
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Algoritmos , Agua Corporal/metabolismo , Interpretación de Imagen Asistida por Computador/métodos , Imagen por Resonancia Magnética/métodos , Espectroscopía de Resonancia Magnética/métodos , Tibia/metabolismo , Adulto , Anciano , Anciano de 80 o más Años , Humanos , Aumento de la Imagen/métodos , Masculino , Persona de Mediana Edad , Porosidad , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
Adenylate kinase plays an important role in cellular energy homeostasis by catalysing the interconversion of adenine nucleotides. The goal of present study was to evaluate the contribution of the adenylate kinase reaction to oxidative ATP synthesis by direct measurements of ATP using (31) P NMR spectroscopy. Results show that AMP can stimulate ATP synthesis in the presence or absence of ADP. In particular, addition of 1 mM AMP to the 0.6 mM ADP superfusion system of isolated superfused mitochondria (contained and maintained in agarose beads) led to a 25% increase in ATP synthesis as measured by the increase in ßATP signal. More importantly, we show that AMP can support ATP synthesis in the absence of ADP, demonstrated as follows. Superfusion of mitochondria without ADP led to the disappearance of ATP γ, α and ß signals and the increase of Pi . Addition of AMP to the medium restored the production of ATP, as demonstrated by the reappearance of γ, α and ß ATP signals, in conjunction with a decrease in Pi , which is being used for ATP synthesis. Polarographic studies showed Mg(2+) dependence of this process, confirming the specificity of the adenylate kinase reaction. Furthermore, data obtained from this study demonstrate, for the first time, that different aspects of the adenylate kinase reaction can be evaluated with (31) P NMR spectroscopy. SIGNIFICANCE OF RESEARCH PARAGRAPH: The data generated in the present study indicate that (31) P NMR spectroscopy can effectively be used to study the adenylate kinase reaction under a variety of conditions. This is important because understanding of adenylate kinase function and/or malfunction is essential to understanding its role in health and disease. The data obtained with (31) P NMR were confirmed by polarographic studies, which further strengthens the robustness of the NMR findings. In summary, (31) P NMR spectroscopy provides a sensitive tool to study adenylate kinase activity in different physiological and pathophysiological conditions, including but not exclusive of, cancer, ischemic injury, hemolytic anemia and neurological problems such as sensorineural deafness.
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Adenosina Monofosfato/metabolismo , Adenosina Trifosfato/biosíntesis , Adenilato Quinasa/metabolismo , Mitocondrias/metabolismo , Miocardio/metabolismo , Consumo de Oxígeno , Animales , Espectroscopía de Resonancia Magnética/métodos , Polarografía/métodos , RatasRESUMEN
Magnetic resonance imaging has previously demonstrated its potential for indirectly mapping myelin density, either by relaxometric detection of myelin water or magnetization transfer. Here, we investigated whether myelin can be detected and possibly quantified directly. We identified the spectrum of myelin in the spinal cord in situ as well as in myelin lipids extracted via a sucrose gradient method, and investigated its spectral properties. High-resolution solution NMR spectroscopy showed the extract composition to be in agreement with myelin's known chemical make-up. The 400-MHz (1)H spectrum of the myelin extract, at 20 °C (room temperature) and 37 °C, consists of a narrow water resonance superimposed on a broad envelope shifted â¼3.5 ppm upfield, suggestive of long-chain methylene protons. Superimposed on this signal are narrow components resulting from functional groups matching the chemical shifts of the constituents making up myelin lipids. The spectrum could be modeled as a sum of super-Lorentzians with a T(2)* distribution covering a wide range of values (0.008-26 ms). Overall, there was a high degree of similarity between the spectral properties of extracted myelin lipids and those found in neural tissue. The normalized difference spectrum had the hallmarks of membrane proteins, not present in the myelin extract. Using 3D radially ramp-sampled proton MRI, with a combination of adiabatic inversion and echo subtraction, the feasibility of direct myelin imaging in situ is demonstrated. Last, the integrated signal from myelin suspensions is shown, both spectroscopically and by imaging, to scale with concentration, suggesting the potential for quantitative determination of myelin density.
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Espectroscopía de Resonancia Magnética/métodos , Vaina de Mielina/química , Médula Espinal/química , Animales , Ratas , Ratas Sprague-DawleyRESUMEN
Recent work has shown that solid-state (1) H and (31) P MRI can provide detailed insight into bone matrix and mineral properties, thereby potentially enabling differentiation of osteoporosis from osteomalacia. However, (31) P MRI of bone mineral is hampered by unfavorable relaxation properties. Hence, accurate knowledge of these properties is critical to optimizing MRI of bone phosphorus. In this work, (31) P MRI signal-to-noise ratio (SNR) was predicted on the basis of T1 and T2 * (effective transverse relaxation time) measured in lamb bone at six field strengths (1.5-11.7 T) and subsequently verified by 3D ultra-short echo-time and zero echo-time imaging. Further, T1 was measured in deuterium-exchanged bone and partially demineralized bone. (31) P T2 * was found to decrease from 220.3 ± 4.3 µs to 98.0 ± 1.4 µs from 1.5 to 11.7 T, and T1 to increase from 12.8 ± 0.5 s to 97.3 ± 6.4 s. Deuteron substitution of exchangeable water showed that 76% of the (31) P longitudinal relaxation rate is due to (1) H-(31) P dipolar interactions. Lastly, hypomineralization was found to decrease T1, which may have implications for (31) P MRI based mineralization density quantification. Despite the steep decrease in the T2 */T1 ratio, SNR should increase with field strength as B0 (0.4) for sample-dominated noise and as B0 (1.1) for coil-dominated noise. This was confirmed by imaging experiments.
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Huesos/fisiología , Calcificación Fisiológica , Campos Magnéticos , Espectroscopía de Resonancia Magnética , Minerales/metabolismo , Fósforo/metabolismo , Animales , Deuterio/metabolismo , Ondas de Radio , Ovinos , Relación Señal-Ruido , Factores de TiempoRESUMEN
GKAs (glucokinase activators) are promising agents for the therapy of Type 2 diabetes, but little is known about their effects on hepatic intermediary metabolism. We monitored the fate of (13)C-labelled glucose in both a liver perfusion system and isolated hepatocytes. MS and NMR spectroscopy were deployed to measure isotopic enrichment. The results demonstrate that the stimulation of glycolysis by GKA led to numerous changes in hepatic metabolism: (i) augmented flux through the TCA (tricarboxylic acid) cycle, as evidenced by greater incorporation of (13)C into the cycle (anaplerosis) and increased generation of (13)C isotopomers of citrate, glutamate and aspartate (cataplerosis); (ii) lowering of hepatic [Pi] and elevated [ATP], denoting greater phosphorylation potential and energy state; (iii) stimulation of glycogen synthesis from glucose, but inhibition of glycogen synthesis from 3-carbon precursors; (iv) increased synthesis of N-acetylglutamate and consequently augmented ureagenesis; (v) increased synthesis of glutamine, alanine, serine and glycine; and (vi) increased production and outflow of lactate. The present study provides a deeper insight into the hepatic actions of GKAs and uncovers the potential benefits and risks of GKA for treatment of diabetes. GKA improved hepatic bioenergetics, ureagenesis and glycogenesis, but decreased gluconeogenesis with a potential risk of lactic acidosis and fatty liver.
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Bencenoacetamidas/farmacología , Glucoquinasa/metabolismo , Hepatocitos/enzimología , Metabolómica/métodos , Animales , Activación Enzimática/efectos de los fármacos , Activación Enzimática/fisiología , Hepatocitos/efectos de los fármacos , Hígado/efectos de los fármacos , Hígado/enzimología , Masculino , Ratas , Ratas Sprague-DawleyRESUMEN
OBJECTIVE: High-resolution MRI methods have been used to evaluate carotid artery atherosclerotic plaque content. The purpose of this study was to assess the performance of high-resolution MRI in evaluation of the quantity and pattern of mineral deposition in carotid endarterectomy (CEA) specimens, with quantitative micro-CT as the gold standard. METHODS AND RESULTS: High-resolution MRI and CT were compared in 20 CEA specimens. Linear regression comparing mineral volumes generated from CT (VCT) and MRI (VMRI) data demonstrated good correlation using simple thresholding (VMRI=-0.01+0.98VCT; R2=0.90; threshold=4xnoise) and k-means clustering methods (VMRI=-0.005+1.38VCT; R2=0.93). Bone mineral density (BMD) and bone mineral content (BMC [mineral mass]) were calculated for CT data and BMC verified with ash weight. Patterns of mineralization like particles, granules, and sheets were more clearly depicted on CT. CONCLUSIONS: Mineral volumes generated from MRI or CT data were highly correlated. CT provided a more detailed depiction of mineralization patterns and provided BMD and BMC in addition to mineral volume. The extent of mineralization as well as the morphology may ultimately be useful in assessing plaque stability.
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Enfermedades de las Arterias Carótidas/diagnóstico por imagen , Enfermedades de las Arterias Carótidas/patología , Imagen por Resonancia Magnética/métodos , Minerales/metabolismo , Tomografía Computarizada por Rayos X/métodos , Adulto , Anciano , Anciano de 80 o más Años , Enfermedades de las Arterias Carótidas/metabolismo , Estudios de Evaluación como Asunto , Femenino , Humanos , Imagen por Resonancia Magnética/normas , Masculino , Persona de Mediana Edad , Reproducibilidad de los Resultados , Tomografía Computarizada por Rayos X/normasRESUMEN
In the present study, noninvasive (31)P and (23)Na(+)-nuclear magnetic resonance (NMR) technology and respirometry were used to compare the effect of high glucose (30 mmol/l) with the effect of the antidiabetic sulfonylurea (SU) compound glyburide (GLY) on energy metabolism, Na(+) flux, insulin, and cAMP release of continuously superfused beta-HC9 cells encapsulated in microscopic agarose beads. Both high glucose and GLY increased oxygen consumption in beta-HC9 cells (15-30%) with a maximal effect at 8 mmol/l for glucose and at 250 nmol/l for GLY. At the same time, insulin release from beta-cells increased by 15- and 25-fold with high glucose or GLY, respectively. The P-creatine (PCr) level was greatly increased and inorganic phosphate (P(i)) was decreased with 30 mmol/l glucose in contrast to the decreased level of PCr and increased P(i) with GLY. ATP levels remained unchanged during both interventions. Studies on isolated mitochondria of beta-HC9 cells showed that GLY added to mitochondria oxidizing glutamine or glutamate abolished the stimulation of respiration by ADP (state 3) meanwhile leaving state 3 respiration unchanged during oxidation of other substrates. Exposure of beta-HC9 cells to 5 mmol/l glucose decreased intracellular Na(+) levels monitored by (23)Na(+)-NMR spectroscopy and 30 mmol/l glucose resulted in a further decrease in cytosolic Na(+). In contrast, Na(+) increased when 1 micro mol/l GLY was added to the perfusate containing 5 mmol/l glucose. These data support the hypothesis that glucose activates the beta-cell through a "push mechanism" due to substrate pressure enhancing fuel flux, energy production, and extrusion of Na(+) from the cells in contrast to SU receptor (SUR)-1 inhibitors, which may modify intermediary and energy metabolism secondarily through a "pull mechanism" due to higher energy demand resulting from increased ion fluxes and the exocytotic work load.
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Metabolismo Energético/efectos de los fármacos , Glucosa/farmacología , Gliburida/farmacología , Consumo de Oxígeno/efectos de los fármacos , Sodio/metabolismo , Adenosina Difosfato/farmacología , Adenosina Trifosfato/metabolismo , Animales , Línea Celular , Ácido Glutámico/metabolismo , Glutamina/metabolismo , Islotes Pancreáticos/efectos de los fármacos , Islotes Pancreáticos/metabolismo , Cinética , Espectroscopía de Resonancia Magnética/métodos , Mitocondrias/efectos de los fármacos , Mitocondrias/metabolismo , Perfusión/métodos , Fosfocreatina/metabolismo , Ratas , Ácido Succínico/metabolismoRESUMEN
The study of rotational and translational diffusion requires the measurement of both T2 and apparent diffusion coefficient (ADC), quantities that are typically measured in separate experiments. The exploitation of echoes generated via multiple coherence transfer pathways offers an opportunity for measuring T2 and ADC values simultaneously in a single experiment. A series of RF pulses can generate multiple echoes via different coherence pathways with each one being uniquely encoded. Here, we demonstrate one pulse sequence that uses an initial theta; RF pulse to generate three coherence orders (C = 0, -1, +1). In the particular version of the method discussed here only two are used (C = 0, +1). Each order is encoded with a different b value from which the ADC is derived. The coherence order echo C = 0 is refocused to quantify T2. The performance of the method--dubbed simultaneous measurement of ADC and relaxation time (SMART)--is demonstrated on a set of samples differing in T2 and ADC achieved by varying the relative volume fractions in mixtures of gadolinium-doped H2O and D2O. The regional SMART derived T2 and ADC agree well with those obtained with conventional double-spin-echo and pulsed gradient spin-echo methods.
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Medios de Contraste/química , Imagen de Difusión por Resonancia Magnética/métodos , Gadolinio DTPA/química , Estudios de Factibilidad , Aumento de la Imagen/métodos , Fantasmas de Imagen , Agua/químicaRESUMEN
Magnetic resonance has the potential to image and quantify two pools of water within bone: free water within the Haversian pore system (transverse relaxation time, T2 > 1 ms), and water hydrogen-bonded to matrix collagen (T2 â¼ 300 to 400 µs). Although total bone water concentration quantified by MRI has been shown to scale with porosity, greater insight into bone matrix density and porosity may be gained by relaxation-based separation of bound and pore water fractions. The objective of this study was to evaluate a recently developed surrogate measurement for matrix density, single adiabatic inversion recovery (SIR) zero echo-time (ZTE) MRI, in human bone. Specimens of tibial cortical bone from 15 donors (aged 27 to 97 years; 8 female and 7 male) were examined at 9.4T field strength using two methods: (1) (1)H ZTE MRI, to capture total (1)H signal, and (2) (1)H SIR-ZTE MRI, to selectively image matrix-associated (1)H signal. Total water, bone matrix, and bone mineral densities were also quantified gravimetrically, and porosity was measured by micro-CT. ZTE apparent total water (1)H concentration was 32.7 ± 3.2 M (range 28.5 to 40.3 M), and was correlated positively with porosity (R(2) = 0.80) and negatively with matrix and mineral densities (R(2) = 0.90 and 0.82, respectively). SIR-ZTE apparent bound water (1)H concentration was 32.9 ± 3.9 M (range 24.4 to 39.8 M), and its correlations were opposite to those of apparent total water: negative with porosity (R(2) = 0.73) and positive with matrix density (R(2) = 0.74) and mineral density (R(2) = 0.72). Porosity was strongly correlated with gravimetric matrix density (R(2) = 0.91, negative) and total water density (R(2) = 0.92, positive). The strong correlations of SIR-ZTE-derived apparent bound water (1)H concentration with ground-truth measurements suggest that this quantitative solid-state MRI method provides a nondestructive surrogate measure of bone matrix density.
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Densidad Ósea , Matriz Ósea/anatomía & histología , Huesos/anatomía & histología , Adulto , Anciano , Anciano de 80 o más Años , Colágeno/química , Femenino , Humanos , Enlace de Hidrógeno , Imagen por Resonancia Magnética , Masculino , Persona de Mediana Edad , Porosidad , Protones , Termogravimetría , Tibia/anatomía & histología , Agua/química , Microtomografía por Rayos XRESUMEN
UNLABELLED: NMR was used to measure matrix water content in normal and hypomineralized cortical bone. Water content showed an inverse relationship with mineral content, suggesting it could serve as a surrogate measure for the bone's degree of mineralization. INTRODUCTION: So far, true bone mineral density (DMB; degree of mineralization of bone) can not be measured nondestructively. MATERIALS AND METHODS: Here, a new technique combining 1H nuclear magnetic resonance (NMR) spectroscopy and deuterium isotope exchange was used to measure water content in cortical bone from two groups of rabbits: a control group and a group fed a low-phosphorus (P) diet to induce hypomineralization of the bone matrix. RESULTS: NMR-derived water content was higher in the P-depleted group and showed an inverse relationship with mineral content (measured gravimetrically and by 31p NMR). Hypomineralized bone was found to be weaker than normal bone as demonstrated by mechanical testing. More importantly, the data showed a strong inverse correlation between water content and bone mechanical properties, which indicates that water content could be predictive of the bone's mechanical competence. CONCLUSIONS: Water content could potentially serve as a surrogate measure for the bone's degree of mineralization, and this technique could be used to study other disorders of mineral homeostasis known to alter the mineralization state of the matrix. Although the method presented here is not suitable for in vivo measurements of bone water content, the authors have previously shown that 1H NMR images of bone can be acquired; thus, noninvasive quantification of bone water may be feasible.
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Densidad Ósea , Espectroscopía de Resonancia Magnética/métodos , Agua/análisis , Animales , Fenómenos Biomecánicos , Deuterio , Protones , ConejosRESUMEN
The direct visualization of axons within their native tissue environment by magnetic resonance (MR) microscopy is presented for the first time in the excised larval sea lamprey spinal cord. A home-built transverse radio frequency coil of 1.5 mm diameter was used in conjunction with a commercial 400 MHz MR microscopy system, implementing both 2-D and 3-D imaging pulse sequences. Images having nominal voxel sizes of 9x9x500 and 9x9x125 microm(3), respectively, in the lamprey spinal cord were obtained, resolving individual Mauthner and Müller axons. Furthermore, architectural changes associated with axonal degeneration were visualized in the spinal cord of one animal, excised 8 weeks after hemisection of the cord. Although the lamprey previously has not been the subject of MR microscopy investigations, these results demonstrate the method's potential for imaging this axon system, which is an important model of spinal cord injury and regeneration.
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Axones , Imagen por Resonancia Magnética/métodos , Microscopía/métodos , Médula Espinal/citología , Animales , Lampreas , Larva , Degeneración Nerviosa/patologíaRESUMEN
BACKGROUND AND PURPOSE: Membrane constituents may play a key role in the magnetization transfer (MT) effect. In lamprey spinal cord, axonal diameters range from <1 microm in the dorsal region to 20-40 microm in the ventral region. There is a corresponding range of axonal, and hence cell membrane, density. These characteristics permit determination of the effect of cell membrane density on MT. The purpose of this study was to characterize regional MT effects in lamprey spinal cord. METHODS: Excised spinal cords from eight sea lampreys were measured with a 9.4-T MR imaging system. MT saturation was applied for spin-echo sequences. The MT ratio (MTR) was calculated in each location (dorsal, lateral, and ventral columns). Spinal cords from five other lampreys were prepared with an antibody to lamprey glial keratin (LCM 29). The percentage of area staining with LCM29 was calculated for each location. RESULTS: Mean MTR (+/- SD) for the dorsal, lateral, and ventral columns were 62.4 +/- 4.2, 59.2 +/- 2.7, and 56.9 +/- 3.0, respectively; all differences were significant (P < .05). Mean LCM29-positive areas for the dorsal, lateral, and ventral columns were 85.1%, 69.7%, and 50.9%, respectively. MTR and percentage LCM29-positive area were significantly correlated (r(2) = 0.98). CONCLUSION: Regional differences in MT effect exist in the lamprey spinal cord. MTR is well correlated with percentage LCM29-positive area. These results support the hypothesis that membrane constituents are at least partly responsible for regional variations in MT effect.
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Imagen Eco-Planar , Queratinas/metabolismo , Lampreas/anatomía & histología , Lampreas/metabolismo , Neuroglía/metabolismo , Médula Espinal/anatomía & histología , Médula Espinal/metabolismo , Animales , Inmunohistoquímica , Técnicas In Vitro , Lampreas/crecimiento & desarrollo , Larva/anatomía & histología , Larva/metabolismo , Médula Espinal/citologíaRESUMEN
Premature infants exposed to hyperoxia suffer acute and long-term pulmonary consequences. Nevertheless, neonates survive hyperoxia better than adults. The factors contributing to neonatal hyperoxic tolerance are not fully elucidated. In contrast to adults, heme oxygenase (HO)-1, an endoplasmic reticulum (ER)-anchored protein, is abundant in the neonatal lung but is not inducible in response to hyperoxia. The latter may be important, because very high levels of HO-1 overexpression are associated with significant oxygen cytotoxicity in vitro. Also, in contrast to adults, HO-1 localizes to the nucleus in neonatal mice exposed to hyperoxia. To understand the mechanisms by which HO-1 expression levels and subcellular localization contribute to hyperoxic tolerance in neonates, lung-specific transgenic mice expressing high or low levels of full-length HO-1 (cytoplasmic, HO-1-FL(H) or HO-1-FL(L)) or C-terminally truncated HO-1 (nuclear, Nuc-HO-1-TR) were generated. In HO-1-FL(L), the lungs had a normal alveolar appearance and lesser oxidative damage after hyperoxic exposure. In contrast, in HO-1-FL(H), alveolar wall thickness with type II cell hyperproliferation was observed as well worsened pulmonary function and evidence of abnormal lung cell hyperproliferation in recovery from hyperoxia. In Nuc-HO-1-TR, the lungs had increased DNA oxidative damage, increased poly (ADP-ribose) polymerase (PARP) protein expression, and reduced poly (ADP-ribose) (PAR) hydrolysis as well as reduced pulmonary function in recovery from hyperoxia. These data indicate that low cytoplasmic HO-1 levels protect against hyperoxia-induced lung injury by attenuating oxidative stress, whereas high cytoplasmic HO-1 levels worsen lung injury by increasing proliferation and decreasing apoptosis of alveolar type II cells. Enhanced lung nuclear HO-1 levels impaired recovery from hyperoxic lung injury by disabling PAR-dependent regulation of DNA repair. Lastly both high cytoplasmic and nuclear expression of HO-1 predisposed to long-term abnormal lung cellular proliferation. To maximize HO-1 cytoprotective effects, therapeutic strategies must account for the specific effects of its subcellular localization and expression levels.
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Citoprotección , Hemo-Oxigenasa 1/metabolismo , Lesión Pulmonar/enzimología , Lesión Pulmonar/patología , Animales , Animales Recién Nacidos , Apoptosis , Carcinogénesis/patología , Proliferación Celular , ADN/metabolismo , Daño del ADN , Modelos Animales de Enfermedad , Células Epiteliales/enzimología , Células Epiteliales/patología , Humanos , Hidrólisis , Hiperoxia/enzimología , Hiperoxia/patología , Hiperoxia/fisiopatología , Pulmón/enzimología , Pulmón/patología , Pulmón/fisiopatología , Lesión Pulmonar/fisiopatología , Imagen por Resonancia Magnética , Ratones , Ratones Transgénicos , Oxidación-Reducción , Estrés Oxidativo , Poli Adenosina Difosfato Ribosa/metabolismo , Poli(ADP-Ribosa) Polimerasas/metabolismo , Alveolos Pulmonares/enzimología , Alveolos Pulmonares/patología , Alveolos Pulmonares/fisiopatología , Pruebas de Función Respiratoria , Fracciones Subcelulares/efectos de los fármacos , Fracciones Subcelulares/enzimologíaRESUMEN
Recent advances in micro-magnetic resonance imaging (microMRI) now allow noninvasive assessment of mechanical properties of trabecular bone (TB) in vivo by micro finite-element analysis. The first aim of this work was to address the implications of limited resolution and signal-to-noise ratio on elastic properties of TB derived under conditions of in vivo imaging via simulation at various resolutions and noise levels on the basis of models derived from microCT images at 21 microm isotropic voxel size from cores of cadaveric human TB (n = 13) from three anatomic sites. The second aim was to compare how elastic constants derived from actual MR images at 9.4 Tesla at 50 microm isotropic voxel size compare with those from high-resolution microCT. Elastic moduli computed from simulated in vivo microMR images were highly correlated with those obtained from microCT (R(2) = 0.99) and the data were relatively immune to noise. Correlations of similar strength were obtained between estimated moduli from microCT and acquired high-field MR images. Systematic errors manifesting in significant deviations of the slopes from unity are caused by higher apparent bone-volume fraction of the MR images but can potentially be corrected with appropriate histogram-standardization techniques.
Asunto(s)
Fémur/patología , Análisis de Elementos Finitos , Vértebras Lumbares/patología , Tibia/patología , Adulto , Anciano , Fenómenos Biomecánicos , Elasticidad , Femenino , Humanos , Modelos Lineales , Imagen por Resonancia Magnética/métodos , Masculino , Persona de Mediana Edad , Reproducibilidad de los ResultadosRESUMEN
We previously showed that agmatine stimulated hepatic ureagenesis. In this study, we sought to determine whether the action of agmatine is mediated via cAMP signaling. A pilot experiment demonstrated that the phosphodiesterase inhibitor, 3-isobutylmethylxanthine (IBMX), inhibited urea synthesis albeit increased [cAMP]. Thus, we hypothesized that IBMX inhibits hepatic urea synthesis independent of [cAMP]. We further theorized that agmatine would negate the IBMX action and improve ureagenesis. Experiments were carried out with isolated mitochondria and (15)NH(4)Cl to trace [(15)N]citrulline production or [5-(15)N]glutamine and a rat liver perfusion system to trace ureagenesis. The results demonstrate that IBMX induced the following: (i) inhibition of the mitochondrial respiratory chain and diminished O(2) consumption during liver perfusion; (ii) depletion of the phosphorylation potential and overall hepatic energetic capacity; (iii) inhibition of [(15)N]citrulline synthesis; and (iv) inhibition of urea output in liver perfusion with little effect on [N-acetylglutamate]. The results indicate that IBMX directly and specifically inhibited complex I of the respiratory chain and carbamoyl-phosphate synthase-I (CPS-I), with an EC(50) about 0.6 mm despite a significant elevation of hepatic [cAMP]. Perfusion of agmatine with IBMX stimulated O(2) consumption, restored hepatic phosphorylation potential, and significantly stimulated ureagenesis. The action of agmatine may signify a cascade effect initiated by increased oxidative phosphorylation and greater ATP synthesis. In addition, agmatine may prevent IBMX from binding to one or more active site(s) of CPS-I and thus protect against inhibition of CPS-I. Together, the data may suggest a new experimental application of IBMX in studies of CPS-I malfunction and the use of agmatine as intervention therapy.
Asunto(s)
1-Metil-3-Isobutilxantina/farmacología , Agmatina/farmacología , Hígado/metabolismo , Mitocondrias Hepáticas/metabolismo , Inhibidores de Fosfodiesterasa/farmacología , Urea/metabolismo , Animales , Carbamoil-Fosfato Sintasa (Amoniaco)/metabolismo , AMP Cíclico/metabolismo , Transporte de Electrón/efectos de los fármacos , Masculino , Consumo de Oxígeno/efectos de los fármacos , Perfusión , Hidrolasas Diéster Fosfóricas/metabolismo , Ratas , Ratas Sprague-DawleyRESUMEN
Q-space imaging (QSI), a diffusion MRI technique, can provide quantitative tissue architecture information at cellular dimensions not amenable by conventional diffusion MRI. By exploiting regularities in molecular diffusion barriers, QSI can estimate the average barrier spacing such as the mean axon diameter in white matter (WM). In this work, we performed ex vivo QSI on cervical spinal cord sections from healthy C57BL/6 mice at 400 MHz using a custom-designed uniaxial 50T/m gradient probe delivering a 0.6 microm displacement resolution capable of measuring axon diameters on the scale of 1 microm. After generating QSI-derived axon diameter maps, diameters were calculated using histology from seven WM tracts (dorsal corticospinal, gracilis, cuneatus, rubrospinal, spinothalamic, reticulospinal, and vestibulospinal tracts) each with different axon diameters. We found QSI-derived diameters from regions drawn in the seven WM tracts (1.1 to 2.1 microm) to be highly correlated (r(2)=0.95) with those calculated from histology (0.8 to 1.8 microm). The QSI-derived values overestimated those obtained by histology by approximately 20%, which is likely due to the presence of extra-cellular signal. Finally, simulations on images of synthetic circular axons and axons from histology suggest that QSI-derived diameters are informative despite diameter and axon shape variation and the presence of intra-cellular and extra-cellular signal. QSI may be able to quantify nondestructively changes in WM axon architecture due to pathology or injury at the cellular level.
Asunto(s)
Axones/ultraestructura , Procesamiento de Imagen Asistido por Computador/métodos , Médula Espinal/ultraestructura , Algoritmos , Animales , Simulación por Computador , Interpretación Estadística de Datos , Ratones , Ratones Endogámicos C57BL , Tractos Piramidales/citología , Tractos Piramidales/ultraestructura , Médula Espinal/citologíaRESUMEN
OBJECTIVE: The aim of this study was to clarify the relative contributions of the amount of oxygen in the blood, and vasoconstriction/dilation responsible for changes in T1 and T2 observed in brain during hyperoxia. METHODS: T1 and T2 values of the cerebral cortex and pituitary gland in mice were determined in room air. After room air was changed to either 100% oxygen (n = 8) or carbogen (n = 8), T1 and T2 values were again determined. Changes in each value with both gases were compared. RESULTS: In both challenges, T1 values of the cerebral cortex decreased, whereas significant T2 prolongation of the cerebral cortex and pituitary gland was demonstrated. However, both cortex and pituitary gland displayed similar responses in T1 and T2 values when exposed to 100% oxygen or carbogen. CONCLUSIONS: Reduction of T1 was introduced by the increased amount of dissolved oxygen in blood, and the increased fraction of oxyhemoglobin caused T2 prolongation. The contribution of vasoconstriction/dilation by carbogen to changes in T1 and T2 may be negligible.