Colorimetric Probe for Mn2+ Using a Mixture of an Anionic Dye and a Cationic Polyelectrolyte in an Aqueous Solution

A novel colorimetric probe for Mn²⁺ was easily prepared by mixing negatively charged alizarin complexone (ALC) with positively charged poly[bis(2-chloroethyl)ether-alt-1,3-bis[3-(dimethylamino)propyl]urea] (PQ-2) in aqueous solutions at pH 6.0. Upon adding Mn²⁺ to ALC alone, the solution underwent no distinct color change, while the mixture displayed selective detection of Mn²⁺ over different physiological and environmentally significant metal ions by an efficient naked-eye color change from red to purple. The detection of Mn²⁺ by the mixture was achieved from the electrostatic interactions between ALC and PQ-2. The quantitative determination of Mn²⁺ was obtained by spectrophotometric measurement and naked-eye observation. This sensing strategy can be an attractive approach for the development of new colorimetric probes due to the advantages such as no organic synthesis, facile fabrication, and simple visual detection.

Manganese-Enhanced Magnetic Resonance Imaging: Application in Central Nervous System Diseases

Manganese-enhanced magnetic resonance imaging (MEMRI) relies on the strong paramagnetism of Mn2+. Mn2+ is a calcium ion analog and can enter excitable cells through voltage-gated calcium channels. Mn2+ can be transported along the axons of neurons via microtubule-based fast axonal transport. Based on these properties, MEMRI is used to describe neuroanatomical structures, monitor neural activity, and evaluate axonal transport rates. The application of MEMRI in preclinical animal models of central nervous system (CNS) diseases can provide more information for the study of disease mechanisms. In this article, we provide a brief review of MEMRI use in CNS diseases ranging from neurodegenerative diseases to brain injury and spinal cord injury.

Applications of Manganese-Enhanced Magnetic Resonance Imaging in Ophthalmology and Visual Neuroscience

Understanding the mechanisms of vision in health and disease requires knowledge of the anatomy and physiology of the eye and the neural pathways relevant to visual perception. As such, development of imaging techniques for the visual system is crucial for unveiling the neural basis of visual function or impairment. Magnetic resonance imaging (MRI) offers non-invasive probing of the structure and function of the neural circuits without depth limitation, and can help identify abnormalities in brain tissues in vivo. Among the advanced MRI techniques, manganese-enhanced MRI (MEMRI) involves the use of active manganese contrast agents that positively enhance brain tissue signals in T1-weighted imaging with respect to the levels of connectivity and activity. Depending on the routes of administration, accumulation of manganese ions in the eye and the visual pathways can be attributed to systemic distribution or their local transport across axons in an anterograde fashion, entering the neurons through voltage-gated calcium channels. The use of the paramagnetic manganese contrast in MRI has a wide range of applications in the visual system from imaging neurodevelopment to assessing and monitoring neurodegeneration, neuroplasticity, neuroprotection, and neuroregeneration. In this review, we present four major domains of scientific inquiry where MEMRI can be put to imperative use — deciphering neuroarchitecture, tracing neuronal tracts, detecting neuronal activity, and identifying or differentiating glial activity. We deliberate upon each category studies that have successfully employed MEMRI to examine the visual system, including the delivery protocols, spatiotemporal characteristics, and biophysical interpretation. Based on this literature, we have identified some critical challenges in the field in terms of toxicity, and sensitivity and specificity of manganese enhancement. We also discuss the pitfalls and alternatives of MEMRI which will provide new avenues to explore in the future.

Chemotherapy-Induced Cognitive Impairment Is Associated with Cytokine Dysregulation and Disruptions in Neuroplasticity

Chemotherapy-induced cognitive impairment, often referred to as "chemobrain," is a common side effect. In this study, mice received three intraperitoneal injections of a combination of docetaxel, adriamycin, and cyclophosphamide (DAC) at 2-day intervals. A water maze test was used to examine cognitive performance, and manganese-enhanced magnetic resonance imaging (MEMRI) was used to examine hippocampal neuronal activity. The whole brain, prefrontal cortex, hippocampus, and blood samples were then collected for cytokine measurement. The DAC-treated mice displayed a significantly shorter duration spent in and fewer entries into the target quadrant of the water maze than the control mice and a pronounced decrease in MEMRI signal intensity in the hippocampal subregions. In a separate experiment using in vivo transcranial two-photon imaging, DAC markedly eliminated dendritic spines without changing the rate of spine formation, leading to a striking loss of spines in the medial prefrontal cortex. DAC treatment resulted in significant elevations in the levels of the proinflammatory cytokines interleukin 6 (IL-6) and tumor necrosis factor-α (TNF-α) and in significant decreases in the levels of the anti-inflammatory cytokines IL-4 and IL-10 in most of the sera and brain tissues examined. The IL-6 and TNF-α levels of several sera and brain tissues showed strong inverse correlations with the duration and number of entries in the target quadrant of the water maze and with the hippocampal MEMRI signal intensity, but also showed striking positive correlations with spine elimination and loss. These results indicate that chemobrain is associated with cytokine dysregulation and disrupted neuroplasticity of the brain.

Longitudinal Assessments of Normal and Perilesional Tissues in Focal Brain Ischemia and Partial Optic Nerve Injury with Manganese-enhanced MRI

Although manganese (Mn) can enhance brain tissues for improving magnetic resonance imaging (MRI) assessments, the underlying neural mechanisms of Mn detection remain unclear. In this study, we used Mn-enhanced MRI to test the hypothesis that different Mn entry routes and spatiotemporal Mn distributions can reflect different mechanisms of neural circuitry and neurodegeneration in normal and injured brains. Upon systemic administration, exogenous Mn exhibited varying transport rates and continuous redistribution across healthy rodent brain nuclei over a 2-week timeframe, whereas in rodents following photothrombotic cortical injury, transient middle cerebral artery occlusion, or neonatal hypoxic-ischemic brain injury, Mn preferentially accumulated in perilesional tissues expressing gliosis or oxidative stress within days. Intravitreal Mn administration to healthy rodents not only allowed tracing of primary visual pathways, but also enhanced the hippocampus and medial amygdala within a day, whereas partial transection of the optic nerve led to MRI detection of degrading anterograde Mn transport at the primary injury site and the perilesional tissues secondarily over 6 weeks. Taken together, our results indicate the different Mn transport dynamics across widespread projections in normal and diseased brains. Particularly, perilesional brain tissues may attract abnormal Mn accumulation and gradually reduce anterograde Mn transport via specific Mn entry routes.

Manganese-Enhanced MRI: Biological Applications in Neuroscience

Magnetic resonance imaging (MRI) is an excellent non-invasive tool to investigate biological systems. The administration of the paramagnetic divalent ion manganese (Mn²⁺) enhances MRI contrast in vivo. Due to similarities between Mn²⁺ and calcium (Ca²⁺), the premise of manganese-enhanced MRI (MEMRI) is that the former may enter neurons and other excitable cells through voltage-gated Ca²⁺ channels. As such, MEMRI has been used to trace neuronal pathways, define morphological boundaries, and study connectivity in morphological and functional imaging studies. In this article, we provide a brief overview of MEMRI and discuss recently published data to illustrate the usefulness of this method, particularly in animal models.

Advanced magnetic resonance spectroscopy and imaging techniques applied to brain development and animal models of perinatal injury

Magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) are widely used in the field of brain development and perinatal brain injury. Due to technical progress the magnetic field strength (B0) of MR systems has continuously increased, favoring (1)H-MRS with quantification of up to 18 metabolites in the brain and short echo time (TE) MRI sequences including phase and susceptibility imaging. For longer TE techniques including diffusion imaging modalities, the benefits of higher B0 have not been clearly established. Nevertheless, progress has also been made in new advanced diffusion models that have been developed to enhance the accuracy and specificity of the derived diffusion parameters. In this review, we will describe the latest developments in MRS and MRI techniques, including high-field (1)H-MRS, phase and susceptibility imaging, and diffusion imaging, and discuss their application in the study of cerebral development and perinatal brain injury.

Characterization of neonatal seizures in an animal model of hypoxic-ischemic encephalopathy

OBJECTIVE

In this study, we use time-locked video and electroencephalography (EEG) recordings to characterize acute seizures and EEG abnormalities in an animal model that replicates many salient features of human neonatal hypoxic-ischemic encephalopathy (HIE) including the brain injury pattern and long-term neurologic outcome.

METHODS

Hypoxia-ischemia (HI) was induced in 7-day-old rats by ligating the right carotid artery and exposing the pups to hypoxia for 2 h (Rice-Vannucci method). To identify seizures and abnormal EEG activity, pups were monitored by video-EEG during hypoxia and at various time points after HI. Occurrence of electroclinical seizures, purely electrographic seizures and other abnormal discharges on EEG, was quantified manually. A power spectrum analysis was done to evaluate the effects of HI on EEG spectra in the 1-50 Hz frequency band.

RESULTS

During hypoxia, all pups exhibit short duration, but frequent electroclinical seizures. Almost all pups continue to have seizures in the immediate period following termination of hypoxia. In more than half of the HI rats, seizures persisted for 24 h; for some of them, the seizures continued for >48 h. Seizures were not observed in any rats at 72 h after HI induction. A significant reduction in background EEG voltage in the cortex ipsilateral to the ligated carotid artery occurred in rats subjected to HI. In addition, purely electrographic seizures, spikes, sharp waves, and brief runs of epileptiform discharges (BREDs) were also observed in these rats.

SIGNIFICANCE

HI induction in P7 rats using the Rice-Vannucci method resulted in the development of seizures and EEG abnormalities similar to that seen in human neonates with HIE. Therefore, we conclude that this is a valid model to test the efficacy of novel interventions to treat neonatal seizures.

In vivo visuotopic brain mapping with manganese-enhanced MRI and resting-state functional connectivity MRI

The rodents are an increasingly important model for understanding the mechanisms of development, plasticity, functional specialization and disease in the visual system. However, limited tools have been available for assessing the structural and functional connectivity of the visual brain network globally, in vivo and longitudinally. There are also ongoing debates on whether functional brain connectivity directly reflects structural brain connectivity. In this study, we explored the feasibility of manganese-enhanced MRI (MEMRI) via 3 different routes of Mn(2+) administration for visuotopic brain mapping and understanding of physiological transport in normal and visually deprived adult rats. In addition, resting-state functional connectivity MRI (RSfcMRI) was performed to evaluate the intrinsic functional network and structural-functional relationships in the corresponding anatomical visual brain connections traced by MEMRI. Upon intravitreal, subcortical, and intracortical Mn(2+) injection, different topographic and layer-specific Mn enhancement patterns could be revealed in the visual cortex and subcortical visual nuclei along retinal, callosal, cortico-subcortical, transsynaptic and intracortical horizontal connections. Loss of visual input upon monocular enucleation to adult rats appeared to reduce interhemispheric polysynaptic Mn(2+) transfer but not intra- or inter-hemispheric monosynaptic Mn(2+) transport after Mn(2+) injection into visual cortex. In normal adults, both structural and functional connectivity by MEMRI and RSfcMRI was stronger interhemispherically between bilateral primary/secondary visual cortex (V1/V2) transition zones (TZ) than between V1/V2 TZ and other cortical nuclei. Intrahemispherically, structural and functional connectivity was stronger between visual cortex and subcortical visual nuclei than between visual cortex and other subcortical nuclei. The current results demonstrated the sensitivity of MEMRI and RSfcMRI for assessing the neuroarchitecture, neurophysiology and structural-functional relationships of the visual brains in vivo. These may possess great potentials for effective monitoring and understanding of the basic anatomical and functional connections in the visual system during development, plasticity, disease, pharmacological interventions and genetic modifications in future studies.

Accelerating phase-encoded proton MR spectroscopic imaging by compressed sensing

PURPOSE

To develop a phase encoding reduction scheme based on compressed sensing (CS) for phase-encoded (1) H MR spectroscopic imaging (MRSI).

MATERIALS AND METHODS

Phantom and in vivo rat brain MRSI experiments were performed at 7 Tesla to examine the performance of CS approach and compare it with the full k-space acquisition. The CS undersampling was performed by acquiring a pseudorandom and density-varying subset of phase encodings. Residual water resonance was first removed from the undersampled k-space dataset before CS reconstruction. The CS reconstruction was performed by a linearized Bregman iteration procedure for efficiency in computing large scale L1 minimization. The spectral and spatial fidelity was evaluated by comparing spectral linewidths and metabolite maps and voxel-wise Bland-Altman analysis.

RESULTS

CS preserved the spectral resolution and metabolite content levels. No spectral broadening was observed, and the estimation biases of the metabolite content levels were no more than 4%. CS clearly preserved the boundaries of metabolite maps but led to slight loss of details in metabolite maps.

CONCLUSION

This study demonstrated the feasibility of the proposed CS approach to accelerate phase-encoded (1) H MRSI.

In vivo manganese-enhanced MRI for visuotopic brain mapping

This study explored the feasibility of localized manganese-enhanced MRI (MEMRI) via 3 different routes of Mn(2+) administrations for visuotopic brain mapping of retinal, callosal, cortico-subcortical, transsynaptic and horizontal connections in normal adult rats. Upon fractionated intravitreal Mn(2+) injection, Mn enhancements were observed in the contralateral superior colliculus (SC) and lateral geniculate nucleus (LGN) by 45-60% at 1-3 days after initial Mn(2+) injection and in the contralateral primary visual cortex (V1) by about 10% at 2-3 days after initial Mn(2+) injection. Direct, single-dose Mn(2+) injection to the LGN resulted in Mn enhancement by 13-21% in V1 and 8-11% in SC of the ipsilateral hemisphere at 8 to 24 hours after Mn(2+) administration. Intracortical, single-dose Mn(2+) injection to the visual cortex resulted in Mn enhancement by 53-65% in ipsilateral LGN, 15-26% in ipsilateral SC, 32-34% in the splenium of corpus callosum and 17-25% in contralateral V1/V2 transition zone at 8 to 24 hours after Mn(2+) administration. Notably, some patchy patterns were apparent near the V1/V2 border of the contralateral hemisphere. Laminar-specific horizontal cortical connections were also observed in the ipsilateral hemisphere. The current results demonstrated the sensitivity of MEMRI for assessing the neuroarchitecture of the visual brains in vivo without depth-limitation, and may possess great potentials for studying the basic neural components and connections in the visual system longitudinally during development, plasticity, pharmacological interventions and genetic modifications.

Porencephaly in dogs and cats: magnetic resonance imaging findings and clinical signs

Magnetic resonance imaging (MRI) features of brain lesions in 5 dogs and 2 cats characterized by extensive cystic changes of the cerebral hemispheres in terms of a porencephaly are presented. Age at diagnosis ranged from 12 weeks to 7 years. MRI findings were confined to the forebrain. Porencephalic lesions appeared as wedge-shaped parenchymal defects connecting the ventricular system and the subarachnoid space or as large cystic defects in the cerebral hemispheres. Although in two adult dogs the porencephalic lesions were asymptomatic, the other animals showed clinical symptoms depending on the affected cerebral area. Three animals had seizures. Interestingly, four animals showed neurological signs normally not localized to the forebrain (nystagmus, hypermetria, ataxia). Whether these clinical signs are related to impaired function of the cerebral cortex or to not recognizable lesions in the cerebello-vestibular system could not be further clarified. Although the defects develop intrauterine or postnatal, the clinical symptoms can occur later in life. The definition of porencephaly as well as its subclassification is not uniform in veterinary medicine. We suggest the term encephaloclastic porencephaly unregarding the underlying cause of the defect, which cannot be further specified by diagnostic imaging.

Iron and iron regulatory proteins in amoeboid microglial cells are linked to oligodendrocyte death in hypoxic neonatal rat periventricular white matter through production of proinflammatory cytokines and reactive oxygen/nitrogen species

This study was aimed to examine the role of iron in causing periventricular white matter (PWM) damage following a hypoxic injury in the developing brain. Along with iron, the expression of iron regulatory proteins (IRPs) and transferrin receptor (TfR), which are involved in iron acquisition, was also examined in the PWM by subjecting 1-d-old Wistar rats to hypoxia. Apart from an increase in iron levels in PWM, Perls' iron staining showed an increase of intracellular iron in the preponderant amoeboid microglial cells (AMCs) in the tissue. In response to hypoxia, the protein levels of IRP1, IRP2, and TfR in PWM and AMCs were significantly increased. In primary microglial cultures, administration of iron chelator deferoxamine reduced the generation of iron-induced reactive oxygen and nitrogen species and proinflammatory cytokines such as tumor necrosis factor-α and interleukin-1β. Primary oligodendrocytes treated with conditioned medium from hypoxic microglia exhibited reduced glutathione levels, increased lipid peroxidation, upregulated caspase-3 expression, and reduced proliferation. This was reversed to control levels on treatment with conditioned medium from deferoxamine treated hypoxic microglia; also, there was reduction in apoptosis of oligodendrocytes. The present results suggest that excess iron derived primarily from AMCs might be a mediator of oligodendrocyte cell death in PWM following hypoxia in the neonatal brain.

Tract-based spatial statistics (TBSS): application to detecting white matter tract variation in mild hypoxic-ischemic neonates

The aim of this study is to employ tract-based spatial statistics (TBSS) to analyze the voxel-wise differences in DTI parameters between normal and mild hypoxic-ischemic (HI) neonatal brains. Forty-one full term neonates (24 normal controls and 17 with mild HI injury) and 31 preterm neonates (20 normal controls and 11 with mild HI injury) underwent T1 weighted imaging, T2 weighted imaging and diffusion tensor imaging (DTI) within 28 days after birth. The voxel differences of fractional anisotropy (FA), λ1, λ2, and λ3 values between mild HI group and control group were analyzed in preterm and full term neonates respectively. The significantly decreased FA with increased λ2, λ3 in corticospinal tract, genu of corpus callosum (GCC), external capsule (EC) and splenium of the corpus callosum (SCC) in mild HI neonates suggested deficits or delays in both myelination and premyelination. Such impaired corticospinal tract, in both preterm and term neonates, may directly lead to the subsequent poor motor performance. Impaired EC and SCC, the additional injured sites observed in full term neonates with mild HI injury, may be causally responsible for the dysfunction in coordination and integration. In conclusion, TBSS provides an objective, independent and sensitive method for DTI data analysis of neonatal white matter alterations after mild HI injury.

In vivo evaluation of retinal and callosal projections in early postnatal development and plasticity using manganese-enhanced MRI and diffusion tensor imaging

The rodents are an excellent model for understanding the development and plasticity of the visual system. In this study, we explored the feasibility of Mn-enhanced MRI (MEMRI) and diffusion tensor imaging (DTI) at 7 T for in vivo and longitudinal assessments of the retinal and callosal pathways in normal neonatal rodent brains and after early postnatal visual impairments. Along the retinal pathways, unilateral intravitreal Mn2+ injection resulted in Mn2+ uptake and transport in normal neonatal visual brains at postnatal days (P) 1, 5 and 10 with faster Mn2+ clearance than the adult brains at P60. The reorganization of retinocollicular projections was also detected by significant Mn2+ enhancement by 2%-10% in the ipsilateral superior colliculus (SC) of normal neonatal rats, normal adult mice and adult rats after neonatal monocular enucleation (ME) but not in normal adult rats or adult rats after monocular deprivation (MD). DTI showed a significantly higher fractional anisotropy (FA) by 21% in the optic nerve projected from the remaining eye of ME rats compared to normal rats at 6 weeks old, likely as a result of the retention of axons from the ipsilaterally uncrossed retinal ganglion cells, whereas the anterior and posterior retinal pathways projected from the enucleated or deprived eyes possessed lower FA after neonatal binocular enucleation (BE), ME and MD by 22%-56%, 18%-46% and 11%-15% respectively compared to normal rats, indicative of neurodegeneration or immaturity of white matter tracts. Along the visual callosal pathways, intracortical Mn2+ injection to the visual cortex of BE rats enhanced a larger projection volume by about 74% in the V1/V2 transition zone of the contralateral hemisphere compared to normal rats, without apparent DTI parametric changes in the splenium of corpus callosum. This suggested an adaptive change in interhemispheric connections and spatial specificity in the visual cortex upon early blindness. The results of this study may help determine the mechanisms of axonal uptake and transport, microstructural reorganization and functional activities in the living visual brains during development, diseases, plasticity and early interventions in a global and longitudinal setting.

Molecular imaging of mesothelioma by detection of manganese-superoxide dismutase activity using manganese-enhanced magnetic resonance imaging

Malignant mesothelioma (MM) is a fatal malignancy with a rapidly increasing incidence in industrialized countries because of the widespread use of asbestos in the past centuries. Early diagnosis of MM is critical for a better prognosis, but this is often difficult because of the lack of disease-specific diagnostic imaging. Here, we report that manganese-enhanced magnetic resonance imaging (MEMRI) represents a promising approach for a more selective mesothelioma imaging by monitoring a high-level expression of manganese-superoxide dismutase (Mn-SOD), which is observed in many MM. We found that most human MM cells overexpressed Mn-SOD protein compared with human mesothelial cells and that NCI-H226 human MM cells highly expressed Mn-SOD and augmented Mn accumulation when loaded with manganese chloride (MnCl(2)). The cells showed marked T(1)-signal enhancement on in vitro MRI after incubation with MnCl(2) because of the T(1) shortening effect of Mn(2+). H226 subcutaneous tumor was preferentially enhanced compared with a lung adenocarcinoma cell tumor and another human MM cell tumor in MnCl(2)-enhanced T(1)-weighted MR image (T(1)WI), correlating with their respective Mn-SOD expression levels. Moreover, in a more clinically relevant setting, H226 xenografted pleural tumor was markedly enhanced and readily detected by MEMRI using manganese dipyridoxyl diphosphate (MnDPDP), a clinically used contrast agent, as well as MnCl(2). Therefore, we propose that MEMRI can be a potentially powerful method for noninvasive detection of MM, with high spatial resolution and marked signal enhancement, by targeting Mn-SOD.

CNS regeneration after chronic injury using a self-assembled nanomaterial and MEMRI for real-time in vivo monitoring

To speed up the process of central nervous system (CNS) recovery after injury, the need for real-time measurement of axon regeneration in vivo is essential to assess the extent of injury, as well as the optimal timing and delivery of therapeutics and rehabilitation. It was necessary to develop a chronic animal model with an in vivo measurement technique to provide a real-time monitoring and feedback system. Using the framework of the 4 P's of CNS regeneration (Preserve, Permit, Promote and Plasticity) as a guide, combined with noninvasive manganese-enhanced magnetic resonance imaging (MEMRI), we show a successful chronic injury model to measure CNS regeneration, combined with an in vivo measurement system to provide real-time feedback during every stage of the regeneration process. We also show that a chronic optic tract (OT) lesion is able to heal, and axons are able to regenerate, when treated with a self-assembling nanofiber peptide scaffold (SAPNS).

FROM THE CLINICAL EDITOR

The authors of this study demonstrate the development of a chronic injury model to measure CNS regeneration, combined with an in vivo measurement system to provide real-time feedback during every stage of the regeneration process. In addition, they determined that chronic optic tract lesions are able to heal with axonal regeneration when treated with a self-assembling nanofiber peptide scaffold (SAPNS).

In vivo retinotopic mapping of superior colliculus using manganese-enhanced magnetic resonance imaging

The superior colliculus (SC) is a dome-shaped subcortical laminar structure in the mammalian midbrain, whose superficial layers receive visual information from the retina in a topological order. Despite the increasing number of studies investigating retinotopic projection in visual brain development and disorders, in vivo, high-resolution 3D mapping of topographic organization in the subcortical visual nuclei has not yet been available. This study explores the capability of 3D manganese-enhanced MRI (MEMRI) at 200 μm isotropic resolution for in vivo retinotopic mapping of the rat SC upon partial transection of the intraorbital optic nerve. One day after intravitreal Mn(2+) injection into both eyes, animals with partial transection at the right superior intraorbital optic nerve in Group 1 (n=8) exhibited a significantly lower T1-weighted signal intensity in the lateral region of the left SC compared to the left medial SC and right control SC. Partial transection toward the temporal or nasal region of the right intraorbital optic nerve in Group 2 (n=7) led to T1-weighted hypointensity in the rostral or caudal region of the left SC, whereas a clear border was observed separating 2 halves of the left SC in all groups. Previous histological and electrophysiological studies showed that the retinal ganglion cell axons emanating from superior, inferior, nasal and temporal retina projected respectively to the contralateral lateral, medial, caudal and rostral SC in rodents. While this topological pattern is preserved in the intraorbital optic nerve, it was shown that partial transection of the superior intraorbital optic nerve led to primary injury predominantly in the superior but not inferior retina and optic nerve. The results of this study demonstrated the sensitivity of submillimeter-resolution MEMRI for in vivo, 3D mapping of the precise retinotopic projections in SC upon reduced anterograde axonal transport of Mn(2+) ions from localized regions of the anterior visual pathways to the subcortical midbrain nuclei. Future MEMRI studies are envisioned that measure the topographic changes in brain development, diseases, plasticity and regeneration therapies in a global and longitudinal setting.

A biological global positioning system: considerations for tracking stem cell behaviors in the whole body

Many recent research studies have proposed stem cell therapy as a treatment for cancer, spinal cord injuries, brain damage, cardiovascular disease, and other conditions. Some of these experimental therapies have been tested in small animals and, in rare cases, in humans. Medical researchers anticipate extensive clinical applications of stem cell therapy in the future. The lack of basic knowledge concerning basic stem cell biology-survival, migration, differentiation, integration in a real time manner when transplanted into damaged CNS remains an absolute bottleneck for attempt to design stem cell therapies for CNS diseases. A major challenge to the development of clinical applied stem cell therapy in medical practice remains the lack of efficient stem cell tracking methods. As a result, the fate of the vast majority of stem cells transplanted in the human central nervous system (CNS), particularly in the detrimental effects, remains unknown. The paucity of knowledge concerning basic stem cell biology--survival, migration, differentiation, integration in real-time when transplanted into damaged CNS remains a bottleneck in the attempt to design stem cell therapies for CNS diseases. Even though excellent histological techniques remain as the gold standard, no good in vivo techniques are currently available to assess the transplanted graft for migration, differentiation, or survival. To address these issues, herein we propose strategies to investigate the lineage fate determination of derived human embryonic stem cells (hESC) transplanted in vivo into the CNS. Here, we describe a comprehensive biological Global Positioning System (bGPS) to track transplanted stem cells. But, first, we review, four currently used standard methods for tracking stem cells in vivo: magnetic resonance imaging (MRI), bioluminescence imaging (BLI), positron emission tomography (PET) imaging and fluorescence imaging (FLI) with quantum dots. We summarize these modalities and propose criteria that can be employed to rank the practical usefulness for specific applications. Based on the results of this review, we argue that additional qualities are still needed to advance these modalities toward clinical applications. We then discuss an ideal procedure for labeling and tracking stem cells in vivo, finally, we present a novel imaging system based on our experiments.

Manganese-enhanced MRI of hypoxic-ischemic brain injuries using Mn-DPDP

In this study, Mn-dipyridoxaldiphosphate (MnDPDP), a clinically approved manganese contrast agent for hepatic and pancreatic imaging, was demonstrated for the first time for manganese-enhanced MRI (MEMRI) in brains of normal young rats (n = 4) and rats with hypoxic-ischemic (H-I) insult at postnatal day 7 (n = 8). After a single intraperitoneal injection of low dosage with 0.1micromol/g in postnatal 14 days, 2D T1-weighted image (T1WIs), T1 maps, T2-weighted images (T2WIs) and T2 maps were acquired at 7 Tesla 1 day before, 1 day and 7 days after MnDPDP injection. The image contrast changes induced by MnDPDP appeared as the hyperintensity in T1WIs and the hypointensity in T2WIs. T1 and T2 values decreased in the regions of Mn enhancement. Such enhancement presented as a delayed pattern that was more pronounced in 7 day after MnDPDP injection, suggesting the sustained Mn accumulation due to MnDPDP. Moreover, the MnDPDP enhancement in H-I brains was more pronounced in the lesion sites and was easily detectable in T1WI, T1 map, T2WI and T2 map. The results demonstrated here support the possibility of using MnDPDP as a 'slow release' Mn(2+) for clinical diagnosis of various neuropathologies.

Experimental protocol for activation-induced manganese-enhanced MRI (AIM-MRI) based on quantitative determination of Mn content in rat brain by fast T1 mapping

In activation-induced manganese-enhanced MRI (AIM-MRI) experiments, differential accumulation of Mn in activated and silent brain areas is generally assessed using T(1)-weighted images and quantified by the enhancement of signal intensity (SI), calculated with reference to SI before Mn administration or to SI of brain regions unaffected by the specific stimulus. However, SI enhancement can be unreliable when animals are removed from and reinserted into the magnet. We have developed an experimental protocol based on repeated intraperitoneal (i.p.) injections of Mn, quantitative determination of T(1), and coregistration of images to a rat brain atlas that allows absolute quantification of Mn concentration in selected brain areas. Results showed that interanimal variability of postcontrast T(1) values was very low (compared to the experimental error in T(1) determinations) allowing detection of differential regional Mn uptake in stimulated and unstimulated animals. In addition we have determined in vivo relaxivity of Mn in brain tissue and its frequency dependence.

Functional MRI of postnatal visual development in normal rat superior colliculi

This study employed blood oxygenation level-dependent functional MRI (BOLD-fMRI) to evaluate the visual responses in the superior colliculus of the developing rat brain from the time of eyelid opening to adulthood. Upon flash illumination to the contralateral eye, the regional BOLD response underwent a systematic increase in amplitude with age especially after the third postnatal week. However, no significant difference in BOLD signal increase was found between postnatal days 14 and 21. Our results constitute the first fMRI report in demonstrating the critical period of visual functions in the rat brain during maturation. This can be potentially useful in establishing the links between changes in relation to visual sensory development.

Functional MRI of postnatal visual development in normal and hypoxic-ischemic-injured superior colliculi

The superior colliculus (SC) is a laminated subcortical structure in the mammalian midbrain, whose superficial layers receive visual information from the retina and the visual cortex. To date, its functional organization and development in the visual system remain largely unknown. This study employed blood oxygenation level-dependent (BOLD) functional MRI to evaluate the visual responses of the SC in normally developing and severe neonatal hypoxic-ischemic (HI)-injured rat brains from the time of eyelid opening to adulthood. MRI was performed to the normal animals (n=7) at postnatal days (P) 14, 21, 28 and 60. In the HI-injured group (n=7), the ipsilesional primary and secondary visual cortices were completely damaged after unilateral ligation of the left common carotid artery at P7 followed by hypoxia for 2 h, and MRI was performed at P60. Upon unilateral flash illumination, the normal contralateral SC underwent a systematic increase in BOLD signal amplitude with age especially after the third postnatal week. However, no significant difference in BOLD signal increase was found between P14 and P21. These findings implied the presence of neurovascular coupling at the time of eyelid opening, and the progressive development of hemodynamic regulation in the subcortical visual system. In the HI-injured group at P60, the BOLD signal increases in both SC remained at the same level as the normal group at P28 though they were significantly lower than the normal group at P60. These observations suggested the residual visual functions on both sides of the subcortical brain, despite the damages to the entire ipsilesional visual cortex. The results of this study constitute important evidence on the progressive maturation of visual functions and hemodynamic responses in the normal subcortical brain, and its functional plasticity upon neonatal HI injury.

In vivo MRI of endogenous stem/progenitor cell migration from subventricular zone in normal and injured developing brains

Understanding the alterations of migratory activities of the endogenous neural stem/progenitor cells (NSPs) in injured developing brains is becoming increasingly imperative for curative reasons. In this study, 10-day-old neonatal rats with and without hypoxic-ischemic (HI) insult at postnatal day 7 were injected intraventricularly with micron-sized iron oxide particles (MPIOs), followed by serial high-resolution MRI at 7 T for 2 weeks. MRI findings were correlated to the histological analysis using iron staining and several immunohistochemical double staining. The results indicated that in normal and HI-injured brains the NSPs from the subventricular zone (SVZ) were labeled by MPIOs, and migrated as newly created cells (iron+/BrdU+), neuroblasts (iron+/nestin+), astrocytes or astrocytes-like progenitor cells (iron+/GFAP+), and mature neurons (iron+/NeuN+). In normal brains, the endogenous NSPs mainly exhibited a tangential pattern in both rostral and caudal directions. The NSP radial migratory pattern could be observed in some rats. In the HI-injured brains during the same developmental period, the NSPs mainly migrated towards the HI lesion sites. The tangential, rostrocaudal migrations could be observed but impaired. These findings suggest that the NSP migratory pathways in SVZ change in response to the HI insult, likely due to the self-repairing efforts known in the neonatal brains. The MRI approach demonstrated here is potentially applicable to the in vivo and longitudinal study of NSP cell activities in developing brains under normal and pathological conditions and in therapeutic interventions.

Early detection of neurodegeneration in brain ischemia by manganese-enhanced MRI

This study aims to employ in vivo manganese-enhanced MRI (MEMRI) to detect neurodegenerative changes in two models of brain ischemia, photothrombotic cortical injury (PCI) and transient middle cerebral artery occlusion (MCAO) in rodents. After systemic Mn(2+) injection to both ischemic models, a close pattern of T1-weighted hyperintensity was observed throughout different brain regions in comparison to the distribution of GFAP, MnSOD and GS immunoreactivities, whereby conventional MRI could hardly detect such. In addition, the infarct volumes in the posterior parts of the brain had significantly reduced after Mn(2+) injection to the MCAO model. It is suggested that exogenous Mn(2+) injection may provide enhanced MEMRI detection of oxidative stress and gliosis early after brain ischemia. Manganese may also mediate infarctions at remote brain regions in transient focal cerebral ischemia before delayed secondary damage takes place.

Does diffusion kurtosis imaging lead to better neural tissue characterization? A rodent brain maturation study

Diffusion kurtosis imaging (DKI) can be used to estimate excess kurtosis, which is a dimensionless measure for the deviation of water diffusion profile from Gaussian distribution. Several recent studies have applied DKI to probe the restricted water diffusion in biological tissues. The directional analysis has also been developed to obtain the directionally specific kurtosis. However, these studies could not directly evaluate the sensitivity of DKI in detecting subtle neural tissue alterations. Brain maturation is known to involve various biological events that can affect water diffusion properties, thus providing a sensitive platform to evaluate the efficacy of DKI. In this study, in vivo DKI experiments were performed in normal Sprague-Dawley rats of 3 different ages: postnatal days 13, 31 and 120 (N=6 for each group). Regional analysis was then performed for 4 white matter (WM) and 3 gray matter (GM) structures. Diffusivity and kurtosis estimates derived from DKI were shown to be highly sensitive to the developmental changes in these chosen structures. Conventional diffusion tensor imaging (DTI) parameters were also computed using monoexponential model, yielding reduced sensitivity and directional specificity in monitoring the brain maturation changes. These results demonstrated that, by measuring directionally specific diffusivity and kurtosis, DKI offers a more comprehensive and sensitive detection of tissue microstructural changes. Such imaging advance can provide a better MR diffusion characterization of neural tissues, both WM and GM, in normal, developmental and pathological states.