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Alan P Koretsky

Publications and source records attributed to Alan P Koretsky.

36 records · Page 2Linked to original sources
PubMed2004

Manganese-enhanced magnetic resonance imaging (MEMRI): methodological and practical considerations.

Manganese-enhanced MRI (MEMRI) is being increasingly used for MRI in animals due to the unique T1 contrast that is sensitive to a number of biological processes. Three specific uses of MEMRI have been demonstrated: to visualize activity in the brain and the heart; to trace neuronal specific connections in the brain; and to enhance the brain cytoarchitecture after a systemic dose. Based on an ever-growing number of applications, MEMRI is proving useful as a new molecular imaging method to visualize functional neural circuits and anatomy as well as function in the brain in vivo. Paramount to the successful application of MEMRI is the ability to deliver Mn2+ to the site of interest at an appropriate dose and in a time-efficient manner. A major drawback to the use of Mn2+ as a contrast agent is its cellular toxicity. Therefore, it is critical to use as low a dose as possible. In the present work the different approaches to MEMRI are reviewed from a practical standpoint. Emphasis is given to the experimental methodology of how to achieve significant, yet safe, amounts of Mn2+ to the target areas of interest.

Animals↗
PubMed2004

Decreasing motion artifacts in calcium-dependent fluorescence transients from the perfused mouse heart using frequency filtering.

A strategy has been developed for the removal of motion artifact and noise in calcium-dependent fluorescence transients from the perfused mouse heart using frequency filtering. An analytical model indicates that the spectral removal of motion artifacts is independent of the phase shift of the motion waveform in the frequency domain, and thus to the time shift (or delay) of motion in the time domain. This is based on the "shift theorem" of Fourier analysis, which avoids erroneous correction of motion artifact when using the motion signal obtained using reflectance from the heart. Several major steps are adopted to implement this model for elimination of motion as well as detection noise from the fluorescence transient signals from the calcium-sensitive probe Rhod-2. These include (1) extracting the fluorescence calcium transient signal from the raw data by using power spectrum density (PSD) in the frequency domain by subtracting the motion recorded using the reflectance of excitation light, (2) digitally filtering out the random noise using multiple bandpass filters centralized at harmonic frequencies of the transients, and (3) extracting high frequency noise with a Gaussian Kernel filter method. The processed signal of transients acquired with excessive motion artifact is comparable to transients acquired with minimal motion obtained by immobilizing the heart against the detection window, demonstrating the usefulness of this technique.

Animals↗
PubMed2004

In vivo detection of neuroarchitecture in the rodent brain using manganese-enhanced MRI.

Visualizing brain anatomy in vivo could provide insight into normal and pathophysiology. Here it is demonstrated that neuroarchitecture can be detected in the rodent brain using MRI after systemic MnCl2. Administration of MnCl2 leads to rapid T1 enhancement in the choroid plexus and circumventricular organs, which spreads to the CSF space in ventricles and periventricular tissue. After 1 day, there was MRI enhancement throughout the brain with high intensity in the pituitary, olfactory bulb, cortex, basal forebrain, hippocampus, basal ganglia, hypothalamus, amygdala, and cerebellum. Contrast obtained enabled visualization of specific features of neuroarchitecture. The arrowhead structure of the dentate gyrus as well as the CA1-CA3 region of the hippocampus and layers in cortex, cerebellum, as well as the olfactory bulb could be readily observed. Preliminary assignments of olfactory bulb layers, cortical layers in frontal and somatosensory cortex, and cerebellum were made. Systemic MnCl2 leads to MRI visualization of neuroarchitecture nondestructively.

Animals↗
PubMed2004

New developments in magnetic resonance imaging of the brain.

Magnetic resonance imaging (MRI) continues to have a large impact on the diagnosis and management of a number of diseases, especially diseases associated with brain injury. The strengths of MRI are the unique contrast that can be obtained, and the fact that it is not harmful and that it can be readily applied to human and animal models. The past decade has seen development of functional MRI techniques that measure aspects of hemodynamics and water diffusion that are playing an important role. Indeed, these techniques are having a major impact on management of brain injury. The development of MRI continues at a rapid pace and a renewed push to increased spatial and temporal resolution will extend the applicability of anatomical and functional MRI. Increased interest in molecular imaging using MRI is increasing the number of processes that can be imaged in the brain. This work reviews some new developments that are being made in anatomical, functional, and molecular MRI of the brain, with comments about usefulness for work in the area of neuroprotection.

Animals↗
PubMed2004

Manganese enhanced magnetic resonance imaging.

Manganese is an essential metal that participates as a co-factor in a number of critical biological functions such as electron transport, detoxification of free radicals, and synthesis of neurotransmitters. Like other heavy metals, high concentrations of manganese are toxic. For example, chronic overexposure to manganese leads to movement disorders. In order to maintain this balance between being an essential participant in enzyme function and being a toxic heavy metal, a rich biology has evolved to transport and store manganese. Paramagnetic forms of manganese ions are potent MRI relaxation agents. Indeed, Mn(2+) was the first contrast agent proposed for use in MRI. Recently, there is renewed interest in combining the strong MRI relaxation effects of Mn(2+) with its unique biology in order to expand the range of information that can be measured by MRI. Manganese Enhanced MRI is being developed to give unique tissue contrast, assess tissue viability, act as a surrogate marker of calcium influx into cells and trace neuronal connections. In this article we review recent work and point out prospects for the future uses of manganese enhanced MRI.

Animals↗
PubMed2003

MRI detection of ferritin iron overload and associated neuronal pathology in iron regulatory protein-2 knockout mice.

Genetic ablation of iron regulatory protein 2 (IRP-2), a protein responsible for post-transcriptional regulation of expression of several iron metabolism proteins, predisposes IRP-2 -/- mice to develop adult onset neurodegenerative disease. Ferric iron reproducibly accumulates within axonal tracts and neuronal cell bodies in discrete regions of the brain, and areas of iron accumulation colocalize with areas of high ferritin expression. To better evaluate the onset and progression of neurodegeneration in IRP-2 -/- mice, we performed a high-resolution magnetic resonance imaging study comparing live, age-matched wild-type and IRP-2 -/- mice, using an 11.7-Tesla magnet and a custom-designed head coil. The mice were perfused after imaging, and iron stains and immunohistochemical studies were performed. We detected increases in the number of pixels with low T(2) values expected from accumulations of iron in IRP-2 -/- mice. Moreover, in several areas of the brain, including the substantia nigra and the superior colliculus, we detected areas with unusually high T(2) values that likely represented accumulation of water. On histopathological examination we discovered relatively small vacuoles in these brain regions of IRP-2 -/- mice. Our ability to gather T(2) data within regions of interest enabled us to define a bimodal T(2) intensity pattern that likely represents both ferritin iron accumulation and its associated pathological consequences within the brain. Our discoveries may have significant applications for the diagnosis and treatment of human diseases if such high-resolution techniques can be adapted for use in human subjects.

Animals↗
PubMed2003

Highly efficient endosomal labeling of progenitor and stem cells with large magnetic particles allows magnetic resonance imaging of single cells.

Tracking transplanted stem cells using magnetic resonance imaging (MRI) could offer biologic insight into homing and engraftment. Ultrasmall dextran-coated iron oxide particles have previously been developed for uptake into cells to allow MRI tracking. We describe a new application of much larger, micron-scale, iron oxide magnetic particles with enhanced MR susceptibility, which enables detection of single cells at resolutions that can be achieved in vivo. In addition, these larger particles possess a fluorophore for histologic confirmation of cell distribution. We demonstrate highly efficient, nontoxic, endosomal uptake of these particles into hematopoietic CD34+ cells and mesenchymal stem cells documented by confocal and electron microscopy. Labeled cells retain biologic activity with preservation of colony-forming ability and differentiation capacity. MRI studies could detect labeled CD34+ cells and mesenchymal stem cells (MSCs) at single cell resolution. This appears to be a promising tool for serial noninvasive monitoring of in vivo cell homing and localization using MRI.

Animals↗
PubMed2003

Expression of myoglobin in the transgenic mouse brain.

The main purpose of this study was to express human myoglobin in mouse brain neurons and investigate the effects of this expression on metabolism and blood flow using phosphorous (31P) NMR spectroscopy and NMR perfusion imaging. Transgenic mice expressing brain myoglobin were created using a cDNA sequence for human myoglobin placed under the transcriptional control of either a human platelet-drived grown factor polypeptide B (PDGF-B) promoter sequence or a rat neuron-specific enolase (NSE) promoter sequence. The presence of myoglobin having a functional, reduced-state, heme group was demonstrated by protein analysis and immunocytochemistry. Expression levels were highest in the hippocampus, cerebellum, and cerebral cortex. No gross morphological adaptations of neural tissue resulting from the expression were observed and no statistically significant differences in the energetic state, as measured by 31P NMR, or baseline cortical perfusion, as measured by an NMR perfusion imaging technique, were found.

Animals↗
PubMed2002

Laminar specificity of functional MRI onset times during somatosensory stimulation in rat.

The blood oxygenation level-dependent (BOLD) response to somatosensory stimulation was measured in alpha-chloralose-anesthetized rats. BOLD fMRI was obtained at 40-ms temporal resolution and spatial resolution of 200 x 200 x 2,000 microm(3) by using a gated activation paradigm in an 11.7 T MRI. Results show a consistent heterogeneity of fMRI onset times and amplitudes. The earliest onset time (0.59 +/- 0.17 s, n = 9) corresponded anatomically to layer IV, with superficial and deeper layers starting significantly later (1.27 +/- 0.43 s in layers I-III, and 1.11 +/- 0.45 s in layer VI). The amplitude of BOLD signal changes also varied with the cortical depth from the pial surface. Changes in the supragranular layers (8.3%) were 44% bigger than changes in the intermediate layers (5.5%), located only approximately 700 microm below, and 144% larger than the bottom layer (3.5%), located approximately 1.4 mm below the pial surface. The data presented demonstrate that BOLD signal changes have distinct amplitude and temporal characteristics, which vary spatially across cortical layers.

Animals↗
PubMed2002

A model of blood-brain barrier permeability to water: accounting for blood inflow and longitudinal relaxation effects.

A noninvasive technique for measuring the permeability of the blood-brain barrier (BBB) to water could help to evaluate changes in the functional integrity of the BBB that occur in different pathologies, such as multiple sclerosis or growth of brain tumor. Recently, Schwarzbauer et al. (Magn Reson Med 1997;37:769-777) proposed an MR method to measure this permeability based on the T(1) reductions induced by injecting various doses of paramagnetic contrast agent. However, this method may be difficult to implement in a clinical environment. Described here is a two-point technique, in which a spatially selective inversion is used to measure T(1) prior to and after injection of an intravascular contrast agent. Measurements made in the rat brain are compared to numerical simulations generated with a physiological model that accounts for blood flow and includes two different blood volumes: nonexchanging and exchanging blood volumes. Our results suggest that BBB permeability could be evaluated from the change in T(1) caused by the vascular contrast agent. This technique might provide an approach for monitoring changes in BBB permeability to water in clinical studies.

Animals↗
PubMed2002

Imaging cortical anatomy by high-resolution MR at 3.0T: detection of the stripe of Gennari in visual area 17.

The brain can be parcellated into numerous anatomical and functional subunits. The classic work by Brodmann (Vergleichende Lokalisationslehre der Grosshirnrinde in ihren Prinzipien dargestellt auf Grund des Zellenbaues. Leipzig: Barth; 1909) identified areas of the cerebral cortex based on histological differences. An alternative to his cytoarchitectonic approach is the myeloarchitectonic approach. MRI has excellent white/gray matter contrast in the brain due to the presence of myelin, and thus seems uniquely suited for in vivo studies of cortical myeloarchitecture. Here it is demonstrated that the stripe or stria of Gennari can be consistently detected in human occipital cortex. T(1)-weighted images obtained at 3T from six of 10 normal volunteers, with resolutions of 350 x 350 x 600 mu clearly demonstrate this myelin-rich intracortical layer. It is concluded that the striate cortex (area 17 of Brodmann) of the human brain can be delineated in vivo on T(1)-weighted images, potentially enabling detection of specific cortical boundaries within individual brains.

Brain Mapping↗
PubMed2002

Dynamic activity-induced manganese-dependent contrast magnetic resonance imaging (DAIM MRI).

Activity-induced manganese-dependent contrast (AIM) MRI is a hemodynamic-independent functional MRI method that used manganese ion as an MR-detectable contrast agent. In AIM, MnCl(2) is infused intra-arterially after the blood-brain barrier (BBB) is opened with a hyperosmolar agent. Upon functional stimulation of the brain, Mn(2+) accumulates in the active region(s) by entering active cells through voltage-gated Ca(2+) channels, causing local signal increases in T(1)-weighted images. The contrast of AIM MRI depends strongly on the depth of anesthesia, and the low levels used in somatosensory stimulation studies can lead to significant nonspecific accumulation of manganese ion throughout the brain. The purpose of this study was to produce an AIM functional map of somatosensory stimulation, which separates the stimulation-specific signal increase from the nonspecific activation due to light anesthesia. A dynamic AIM (DAIM) paradigm was developed, which used sequential MR scans during MnCl(2) infusion, prior to and following functional stimulation of the brain. Stimulation-specific functional maps were produced using time-course analysis. The new method was tested during glutamate administration and electric stimulation of the rat forepaw. It was shown that DAIM maps are better confined to the specific region of brain activated by somatosensory stimulation as compared to AIM MRI.

Analysis of Variance↗
PubMed2002

Tracing odor-induced activation in the olfactory bulbs of mice using manganese-enhanced magnetic resonance imaging.

Ithas previously been demonstrated that it is possible to map active regions of the brain using MRI relying on the fact that Mn(2+) ion enters excitable cells through voltage-gated calcium channels and is an excellent relaxation agent. In addition, Mn(2+) has been shown to trace neuronal connections in the mouse olfactory and visual systems, enabling MRI neuronal tract tracing. The purpose of the present studies was to determine if these two properties could be combined to trace Mn(2+) from sites of activation in the olfactory epithelium to the olfactory bulb thereby localizing regions within the olfactory bulb that respond to a particular odor. Mice were exposed to an aerosolized solution containing either a high pheromone content odor (male mouse urine) or amyl acetate plus MnCl(2). In both cases the odors caused a localized T(1) MRI enhancement in the olfactory epithelium and bulb that was dependent upon the presence of Mn(2+). The high pheromone containing solution caused enhancement in the anatomically correct location of the accessory olfactory bulb. Amyl acetate also caused T(1)-weighted MRI enhancement in specific regions of the olfactory bulb. These areas showing activation agree well with previous 2-deoxyglucose and BOLD fMRI results in the rat. Using manganese-enhanced MRI (MEMRI) it should be possible to rapidly map a variety of odors. Furthermore, since the effects of activation are imaged after the activation protocol it should be possible to take the time to obtain very high resolution images and make MEMRI maps from awake behaving animals.

Animals↗
PubMed2002

Transgenic livers expressing mitochondrial and cytosolic CK: mitochondrial CK modulates free ADP levels.

The function of creatine kinase (CK) and its effect on phosphorus metabolites was studied in livers of transgenic mice expressing human ubiquitous mitochondrial CK (CK-Mit) and rat brain CK (CK-B) isoenzymes and their combination. (31)P NMR spectroscopy and saturation transfer were recorded in livers of anesthetized mice to measure high-energy phosphates and hepatic CK activity. CK reaction velocity was related to total enzyme activity irrespective of the isoenzyme expressed, and it increased with increasing concentrations of creatine (Cr). The fluxes mediated by both isoenzymes in both directions (phosphocreatine or ATP synthesis) were equal. Over a 20-fold increase in CK-Mit activity (28-560 micromol. g wet wt(-1). min(-1)), the fraction of phosphorylated Cr increased 1.6-fold. Hepatic free ADP concentrations calculated by assuming equilibrium of the CK-catalyzed reaction in vivo decreased from 84 +/- 9 to 38 +/- 4 nmol/g wet wt. Calculated free ADP levels in mice expressing high levels of CK-B (920-1,635 micromol. g wet wt(-1). min(-1)) were 52 +/- 6 nmol/g wet wt. Mice expressing both isoenzymes had calculated free ADP levels of 36 +/- 4 nmol/g wet wt. These findings indicate that CK-Mit catalyzes its reaction equally well in both directions and can lower hepatic apparent free ADP concentrations.

Adenosine Diphosphate↗
PubMed2002

alpha-Adrenergic response and myofilament activity in mouse hearts lacking PKC phosphorylation sites on cardiac TnI.

Protein kinase C (PKC)-mediated phosphorylation of cardiac myofilament (MF) proteins has been shown to depress the actomyosin interaction and may be important during heart failure. Biochemical studies indicate that phosphorylation of Ser(43) and Ser(45) of cardiac troponin I (cTnI) plays a substantial role in the PKC-mediated depression. We studied intact and detergent-extracted papillary muscles from nontransgenic (NTG) and transgenic (TG) mouse hearts that express a mutant cTnI (Ser43Ala, Ser45Ala) that lacks specific PKC-dependent phosphorylation sites. Treatment of NTG papillary muscles with phenylephrine (PE) resulted in a transient increase and a subsequent 62% reduction in peak twitch force. TG muscles showed no transient increase and only a 45% reduction in force. There was a similar difference in maximum tension between NTG and TG fiber bundles that had been treated with a phorbol ester and had received subsequent detergent extraction. Although levels of cTnI phosphorylation correlated with these differences, the TG fibers also demonstrated a decrease in phosphorylation of cardiac troponin T. The PKC-specific inhibitor chelerythrine inhibited these responses. Our data provide evidence that specific PKC-mediated phosphorylation of Ser(43) and Ser(45) of cTnI plays an important role in regulating force development in the intact myocardium.

Actin Cytoskeleton↗
PubMedDate not supplied

Improved stem cell MR detectability in animal models by modification of the inhalation gas.

In vivo monitoring of cells labeled with paramagnetic iron oxide particles by magnetic resonance imaging (MRI) is complicated by intrinsic contrast of blood vessels. Distinction between T2* effects caused by blood vessels from those caused by labeled cells was so far only possible after carefully following the location of hypointense regions through subsequent slices of T2*-weighted 3-D MRI datasets, a procedure that is time consuming and not always reliable in the case of smaller blood vessels. Here, we demonstrate that the modification of the inhalation gas mixture from the routinely used composition 35% O2 and 65% N2O to a mixture containing 95% O2 and 5% CO2 results in a contrast suppression of most small blood vessels and reduces the intrinsic T2* effect of large vessels dramatically in an animal model. This change in protocol of physiological conditions was well tolerated by all studied animals, even over prolonged experimental times. The changed inhalation gas mixture thus provides a more reliable identification method for small clusters of iron oxide labeled cells in vivo.

Anesthetics, Inhalation↗