Blood-oxygenation level dependent (BOLD) image contrast in magnetic resonance imaging (MRI) has b... more Blood-oxygenation level dependent (BOLD) image contrast in magnetic resonance imaging (MRI) has been widely used in the field of functional imaging to interpret changes in focal brain activity in response to stimuli. The BOLD image contrast relies on activation-induced changes in the magnetic properties of blood (Ogawa et al, 1990; 1993a; 1993b; Shulman et al., 1993; Kennan et al., 1994). The presence of paramagnetic deoxyhemoglobin in the microvasculature creates a magnetic susceptibility difference between the vessels and the surrounding tissue, thus producing a microscopic magnetic field gradient. The microscopic field gradients affect the value of R2* (i.e., apparent transverse relaxation rate of tissue water) which can be mapped by a gradient-echo MRI sequence. The equilibrium between deoxy- and oxyhemoglobin can be shifted by altering the blood oxygenation, and since deoxy- and oxyhemoglobin are para- and diamagnetic, respectively, BOLD image contrast can be created, whereby hemoglobin acts as an endogenous MRI contrast agent. A BOLD functional MRI sequence measures the changes in R2* upon activation. The quantitative change in R2* is determined by parameters which influence the microscopic field gradient such as the geometry of vessels, static magnetic field strength, and the concentration of deoxyhemoglobin within the vessels (Ogawa et al., 1993a; 1993b; Kennan et al., 1994). The concentration of deoxyhemoglobin or the local blood oxygenation fraction (Y) in the microvasculature is determined by the regional values of cerebral metabolic rates of oxygen consumption (CMRO2), cerebral blood flow (CBF), and volume (CBV) (Ogawa et al., 1993a; 1993b; Kennan et al., 1994). While geometry and morphology of microvessels are important for the basal BOLD image contrast at a particular magnetic field strength, it is only the change in concentration of deoxyhemoglobin, due to a short-lived and/or transient physiological perturbation, that is important for being able to quantitate the BOLD signal change for functional MRI (see Appendix).
Purpose:Deuterium Metabolic Imaging (DMI) combined with [6,6’-2H2]-glucose has the potential to d... more Purpose:Deuterium Metabolic Imaging (DMI) combined with [6,6’-2H2]-glucose has the potential to detect glycogen synthesis in the liver. However, the similar chemical shifts of [6,6’-2H2]-glucose and [6,6’-2H2]-glycogen in the 2H NMR spectrum make unambiguous detection and separation difficult in vivo, in contrast to comparable approaches using 13C MRS. Here we investigate the NMR visibility of 2H-labeled glycogen to better understand its potential contribution to the observed signal in liver following administration of [6,6’-2H2]-glucose.Methods:Mice were provided drinking water containing 2H-labeled glucose. High resolution NMR analyses was performed of isolated liver glycogen in solution, before and after the addition of the glucose releasing enzyme amyloglucosidase.Results:2H-labeled glycogen was barely detectable in solution using 2H NMR, due to the very short T2 (< 2 ms) of 2H-labeled glycogen, giving a spectral line width that is more than five times as broad as that of 13C-labeled glycogen (T2 ~ 10 ms).Conclusion:2H-labeled glycogen is not detectable with 2H MRS(I) under in vivo conditions, leaving 13C MRS as the preferred technique for in vivo detection of glycogen.
Using 1H spectroscopy, we measured occipital lobe GABA levels serially in 18 patients enrolled in... more Using 1H spectroscopy, we measured occipital lobe GABA levels serially in 18 patients enrolled in an ongoing open label trial of vigabatrin. Brain GABA levels were elevated twofold in patients taking vigabatrin (3 to 4 g/d) compared with nonepileptic subjects. Serial measurements suggested that brain GABA rose in proportion to vigabatrin dose up to 3 g/d. Doubling the dose from 3 to 6 g/d failed to increase brain GABA further. Serial measurements on three patients taking 6 g/d showed a gradual decrease in brain GABA in two patients over 1 to 2 years of treatment. These observations suggest that GABA synthesis may decrease at high GABA levels.
Three mouse lines with altered growth hormone (GH) signaling were used to study GHÕs role in adip... more Three mouse lines with altered growth hormone (GH) signaling were used to study GHÕs role in adiposity. Dwarf GH receptor knockout mice (GHR)/)) and bovine GH antagonist expressing mice (GHA) had an increased percent body fat with most of the excess fat mass accumulating in the subcutaneous region. Giant bovine GH expressing mice (bGH) had a reduced percent body fat. Only GHA mice consumed significantly more food per body weight. Serum leptin levels were significantly increased in GHA mice and decreased in bGH mice but unchanged in the GHR)/) mice. Interestingly, serum adiponectin levels were significantly increased in the GHR)/) and GHA lines but decreased in bGH mice. These data suggest that suppression or absence of GH action and enhanced GH action indeed have opposite metabolic effects in terms of adiposity. Interestingly, adiponectin levels were positively correlated with previously reported insulin sensitivity of these mice, but also positively correlated with adiposity, which is contrary to findings in other mouse models. Thus, adiponectin levels were negatively correlated with GH function suggesting a role for adiponectin in GH-induced insulin resistance.
We determined cerebral intracellular pH in living rabbits and rats under physiologic conditions, ... more We determined cerebral intracellular pH in living rabbits and rats under physiologic conditions, using phosphorus NMR spectroscopy and new titration curves thought to be appropriate for brain. Mean values for the two species were, respectively, 7.14 +/- 0.04 (SD) and 7.13 +/- 0.03. These are toward the alkaline end of the range of values obtained by other methods, as values reported by other NMR workers also tend to be.
Proceedings of the National Academy of Sciences of the United States of America, May 1, 1981
13C NMR was used to follow the metabolism of [2-'3C]acetate and [1-_3C]acetate in aerobic suspens... more 13C NMR was used to follow the metabolism of [2-'3C]acetate and [1-_3C]acetate in aerobic suspensions of Saccharomyces cerevisiae. In the experiment with [2-'3C]acetate, the 13C label appeared first in glutamate C4 and subsequently in glutamate C2 and C3. After exhaustion of the acetate, the glutamate signals diminished and the aspartate C2 and C3 peaks increased. During a subsequent chase experiment with unlabeled acetate, the aspartate peaks decreased and the glutamate C2 and C3 peaks increased in intensity. These observations are interpreted in terms of an interplay between the glutamic-oxalacetic transaminase and Krebs cycle activity. This interpretation was confirmed by an experiment with the transaminase inhibitor 2-amino oxyacetate. During all of these experiments, we observed the formation of trehalose. The NMR gives a direct measurement of the label distribution and from that information it followed that the flows through the glyoxylate and the Krebs cycles are comparable. The intermediates citrate, succinate, fumarate, malate, phosphoenolpyruvate, 3-phosphoglycerate, and glucose 6-phosphate were identified in a 13C NMR spectrum of a perchloric acid extract taken during the metabolism of [2-'3C]acetate. Enrichment of the glutamate C5 position shows the existence of a futile cycle in which phosphoenolpyruvate, formed from oxaloacetate, returns to the Krebs cycle through pyruvate and acetyl CoA.
Regional rates of 13C incorporation from glucose to glutamate were detected in anesthetized rat b... more Regional rates of 13C incorporation from glucose to glutamate were detected in anesthetized rat brain in vivo at 7T with high temporal and spatial resolution using NMR method ICED PEPSI (in vivo carbon edited detection with proton echo planar spectroscopic imaging). Time courses of regional glutamate 13C turnover were fitted by a metabolic model to obtain regional tri-carboxylic acid (TCA) cycle flux and cerebral metabolic rate of oxygen consumption (CMRO2) in each voxel (8 microL) of rat cortex. CMRO2 maps obtained for rats under either alpha-chloralose or morphine anesthesia revealed average cortical values of 1.5 +/- 0.2 (n = 3) and 3.2 +/- 0.3 (n = 4) mumol/g/min, respectively. These values of CMRO2 are in good agreement with previous cortical measurements with coarser spatial resolution. The heterogeneity within each map, which depicted predominantly gray and white matter differences, was significantly greater under morphine (higher cortical activity) than under-alpha-chloralose (lower cortical activity) anesthesia. The regional variations in the basal awake state, which are expected to be even greater, should be considered to avoid partial-volume artifacts in functional activation studies of awake subjects.
Blood-oxygenation level dependent (BOLD) image contrast in magnetic resonance imaging (MRI) has b... more Blood-oxygenation level dependent (BOLD) image contrast in magnetic resonance imaging (MRI) has been widely used in the field of functional imaging to interpret changes in focal brain activity in response to stimuli. The BOLD image contrast relies on activation-induced changes in the magnetic properties of blood (Ogawa et al, 1990; 1993a; 1993b; Shulman et al., 1993; Kennan et al., 1994). The presence of paramagnetic deoxyhemoglobin in the microvasculature creates a magnetic susceptibility difference between the vessels and the surrounding tissue, thus producing a microscopic magnetic field gradient. The microscopic field gradients affect the value of R2* (i.e., apparent transverse relaxation rate of tissue water) which can be mapped by a gradient-echo MRI sequence. The equilibrium between deoxy- and oxyhemoglobin can be shifted by altering the blood oxygenation, and since deoxy- and oxyhemoglobin are para- and diamagnetic, respectively, BOLD image contrast can be created, whereby hemoglobin acts as an endogenous MRI contrast agent. A BOLD functional MRI sequence measures the changes in R2* upon activation. The quantitative change in R2* is determined by parameters which influence the microscopic field gradient such as the geometry of vessels, static magnetic field strength, and the concentration of deoxyhemoglobin within the vessels (Ogawa et al., 1993a; 1993b; Kennan et al., 1994). The concentration of deoxyhemoglobin or the local blood oxygenation fraction (Y) in the microvasculature is determined by the regional values of cerebral metabolic rates of oxygen consumption (CMRO2), cerebral blood flow (CBF), and volume (CBV) (Ogawa et al., 1993a; 1993b; Kennan et al., 1994). While geometry and morphology of microvessels are important for the basal BOLD image contrast at a particular magnetic field strength, it is only the change in concentration of deoxyhemoglobin, due to a short-lived and/or transient physiological perturbation, that is important for being able to quantitate the BOLD signal change for functional MRI (see Appendix).
Purpose:Deuterium Metabolic Imaging (DMI) combined with [6,6’-2H2]-glucose has the potential to d... more Purpose:Deuterium Metabolic Imaging (DMI) combined with [6,6’-2H2]-glucose has the potential to detect glycogen synthesis in the liver. However, the similar chemical shifts of [6,6’-2H2]-glucose and [6,6’-2H2]-glycogen in the 2H NMR spectrum make unambiguous detection and separation difficult in vivo, in contrast to comparable approaches using 13C MRS. Here we investigate the NMR visibility of 2H-labeled glycogen to better understand its potential contribution to the observed signal in liver following administration of [6,6’-2H2]-glucose.Methods:Mice were provided drinking water containing 2H-labeled glucose. High resolution NMR analyses was performed of isolated liver glycogen in solution, before and after the addition of the glucose releasing enzyme amyloglucosidase.Results:2H-labeled glycogen was barely detectable in solution using 2H NMR, due to the very short T2 (< 2 ms) of 2H-labeled glycogen, giving a spectral line width that is more than five times as broad as that of 13C-labeled glycogen (T2 ~ 10 ms).Conclusion:2H-labeled glycogen is not detectable with 2H MRS(I) under in vivo conditions, leaving 13C MRS as the preferred technique for in vivo detection of glycogen.
Using 1H spectroscopy, we measured occipital lobe GABA levels serially in 18 patients enrolled in... more Using 1H spectroscopy, we measured occipital lobe GABA levels serially in 18 patients enrolled in an ongoing open label trial of vigabatrin. Brain GABA levels were elevated twofold in patients taking vigabatrin (3 to 4 g/d) compared with nonepileptic subjects. Serial measurements suggested that brain GABA rose in proportion to vigabatrin dose up to 3 g/d. Doubling the dose from 3 to 6 g/d failed to increase brain GABA further. Serial measurements on three patients taking 6 g/d showed a gradual decrease in brain GABA in two patients over 1 to 2 years of treatment. These observations suggest that GABA synthesis may decrease at high GABA levels.
Three mouse lines with altered growth hormone (GH) signaling were used to study GHÕs role in adip... more Three mouse lines with altered growth hormone (GH) signaling were used to study GHÕs role in adiposity. Dwarf GH receptor knockout mice (GHR)/)) and bovine GH antagonist expressing mice (GHA) had an increased percent body fat with most of the excess fat mass accumulating in the subcutaneous region. Giant bovine GH expressing mice (bGH) had a reduced percent body fat. Only GHA mice consumed significantly more food per body weight. Serum leptin levels were significantly increased in GHA mice and decreased in bGH mice but unchanged in the GHR)/) mice. Interestingly, serum adiponectin levels were significantly increased in the GHR)/) and GHA lines but decreased in bGH mice. These data suggest that suppression or absence of GH action and enhanced GH action indeed have opposite metabolic effects in terms of adiposity. Interestingly, adiponectin levels were positively correlated with previously reported insulin sensitivity of these mice, but also positively correlated with adiposity, which is contrary to findings in other mouse models. Thus, adiponectin levels were negatively correlated with GH function suggesting a role for adiponectin in GH-induced insulin resistance.
We determined cerebral intracellular pH in living rabbits and rats under physiologic conditions, ... more We determined cerebral intracellular pH in living rabbits and rats under physiologic conditions, using phosphorus NMR spectroscopy and new titration curves thought to be appropriate for brain. Mean values for the two species were, respectively, 7.14 +/- 0.04 (SD) and 7.13 +/- 0.03. These are toward the alkaline end of the range of values obtained by other methods, as values reported by other NMR workers also tend to be.
Proceedings of the National Academy of Sciences of the United States of America, May 1, 1981
13C NMR was used to follow the metabolism of [2-'3C]acetate and [1-_3C]acetate in aerobic suspens... more 13C NMR was used to follow the metabolism of [2-'3C]acetate and [1-_3C]acetate in aerobic suspensions of Saccharomyces cerevisiae. In the experiment with [2-'3C]acetate, the 13C label appeared first in glutamate C4 and subsequently in glutamate C2 and C3. After exhaustion of the acetate, the glutamate signals diminished and the aspartate C2 and C3 peaks increased. During a subsequent chase experiment with unlabeled acetate, the aspartate peaks decreased and the glutamate C2 and C3 peaks increased in intensity. These observations are interpreted in terms of an interplay between the glutamic-oxalacetic transaminase and Krebs cycle activity. This interpretation was confirmed by an experiment with the transaminase inhibitor 2-amino oxyacetate. During all of these experiments, we observed the formation of trehalose. The NMR gives a direct measurement of the label distribution and from that information it followed that the flows through the glyoxylate and the Krebs cycles are comparable. The intermediates citrate, succinate, fumarate, malate, phosphoenolpyruvate, 3-phosphoglycerate, and glucose 6-phosphate were identified in a 13C NMR spectrum of a perchloric acid extract taken during the metabolism of [2-'3C]acetate. Enrichment of the glutamate C5 position shows the existence of a futile cycle in which phosphoenolpyruvate, formed from oxaloacetate, returns to the Krebs cycle through pyruvate and acetyl CoA.
Regional rates of 13C incorporation from glucose to glutamate were detected in anesthetized rat b... more Regional rates of 13C incorporation from glucose to glutamate were detected in anesthetized rat brain in vivo at 7T with high temporal and spatial resolution using NMR method ICED PEPSI (in vivo carbon edited detection with proton echo planar spectroscopic imaging). Time courses of regional glutamate 13C turnover were fitted by a metabolic model to obtain regional tri-carboxylic acid (TCA) cycle flux and cerebral metabolic rate of oxygen consumption (CMRO2) in each voxel (8 microL) of rat cortex. CMRO2 maps obtained for rats under either alpha-chloralose or morphine anesthesia revealed average cortical values of 1.5 +/- 0.2 (n = 3) and 3.2 +/- 0.3 (n = 4) mumol/g/min, respectively. These values of CMRO2 are in good agreement with previous cortical measurements with coarser spatial resolution. The heterogeneity within each map, which depicted predominantly gray and white matter differences, was significantly greater under morphine (higher cortical activity) than under-alpha-chloralose (lower cortical activity) anesthesia. The regional variations in the basal awake state, which are expected to be even greater, should be considered to avoid partial-volume artifacts in functional activation studies of awake subjects.
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