In vivo 3D MRI staining of mouse brain after subcutaneous application of MnCl2

Harnessing axonal transport to map reward circuitry: Differing brain-wide projections from medial prefrontal cortical domains

Neurons project long axons that contact other distant neurons. Neurons in the medial prefrontal cortex project into the limbic system to regulate responses to reward or threat. Diminished neural activity in prefrontal cortex is associated with loss of executive function leading to drug use, yet the specific circuitry that mediate these effects is unknown. Different regions within the medial prefrontal cortex may project to differing limbic system nuclei. Here, we exploited the cell biology of intracellular membrane trafficking, fast axonal transport, to map projections from two adjacent medial prefrontal cortical regions. We used Mn(II), a calcium analog, to trace medial prefrontal cortical projections in the living animal by magnetic resonance imaging (MRI). Mn(II), a contrast agent for MRI, enters neurons through voltage-activated calcium channels and relies on kinesin-1 and amyloid-precursor protein to transport out axons to distal destinations. Aqueous MnCl2 together with fluorescent dextran (3--5 nL) was stereotactically injected precisely into two adjacent regions of the medial prefrontal cortex: anterior cingulate area (ACA) or infralimbic/prelimbic (IL/PL) region. Projections were traced, first live by manganese-enhanced MRI (MEMRI) at four time points in 3D, and then after fixation by microscopy. Data-driven unbiased voxel-wise statistical maps of aligned normalized MR images after either ACA or IL/PL injections revealed statistically significant progression of Mn(II) over time into deeper brain regions: dorsal striatum, globus pallidus, amygdala, hypothalamus, substantia nigra, dorsal raphe and locus coeruleus. Quantitative comparisons of these distal accumulations at 24 h revealed dramatic differences between ACA and IL/PL injection groups throughout the limbic system, and most particularly in subdomains of the hypothalamus. ACA projections targeted dorsomedial nucleus of the hypothalamus, posterior part of the periventricular region and mammillary body nuclei as well as periaqueductal gray, while IL/PL projections accumulated in anterior hypothalamic areas and lateral hypothalamic nuclei as well as amygdala. As hypothalamic subsegments relay CNS activity to the body, our results suggest new concepts about mind-body relationships and specific roles of distinct yet adjacent medial prefrontal cortical segments. Our MR imaging strategy, when applied to follow other cell biological processes in the living organism, will undoubtedly lead to an expanded perspective on how minute details of cellular processes influence whole body health and wellbeing.

Harnessing axonal transport to map reward circuitry: Differing brain-wide projections from medial forebrain domains

Neurons project long axons that contact other distant neurons. Projections can be mapped by hijacking endogenous membrane trafficking machinery by introducing tracers. To witness functional connections in living animals, we developed a tracer detectible by magnetic resonance imaging (MRI), Mn(II). Mn(II) relies on kinesin-1 and amyloid-precursor protein to travel out axons. Within 24h, projection fields of cortical neurons can be mapped brain-wide with this technology. MnCl2 was stereotactically injected either into anterior cingulate area (ACA) or into infralimbic/prelimbic (IL/PL) of medial forebrain (n=10-12). Projections were imaged, first by manganese-enhanced MRI (MEMRI) live, and then after fixation by microscopy. MR images were collected at 100μm isotropic resolution (~5 neurons) in 3D at four time points: before and at successive time points after injections. Images were preprocessed by masking non-brain tissue, followed by intensity scaling and spatial alignment. Actual injection locations, measured from post-injection MR images, were found to be 0.06, 0.49 and 0.84mm apart between cohorts, in R-L, A-P, and D-V directions respectively. Mn(II) enhancements arrived in hindbrains by 24h in both cohorts, while co-injected rhodamine dextran was not detectible beyond immediate subcortical projections. Data-driven unbiased voxel-wise statistical maps after ACA injections revealed significant progression of Mn(II) distally into deeper brain regions: globus pallidus, dorsal striatum, amygdala, hypothalamus, substantia nigra, dorsal raphe and locus coeruleus. Accumulation was quantified as a fraction of total volume of each segment containing significantly enhanced voxels (fractional accumulation volumes), and results visualized in column graphs. Unpaired t-tests between groups of brain-wide voxel-wise intensity profiling by either region of interest (ROI) measurements or statistical parametric mapping highlighted distinct differences in distal accumulation between injection sites, with ACA projecting to periaqueductal gray and IL/PL to basolateral amygdala (p<0.001 FDR). Mn(II) distal accumulations differed dramatically between injection groups in subdomains of the hypothalamus, with ACA targeting dorsal medial, periventricular region and mammillary body nuclei, while IL/PL went to anterior hypothalamic areas and lateral hypothalamic nuclei. Given that these hypothalamic subsegments communicate activity in the central nervous system to the body, these observations describing distinct forebrain projection fields will undoubtedly lead to newer insights in mind-body relationships.

Cell specificity of Manganese-enhanced MRI signal in the cerebellum

Magnetic Resonance Imaging (MRI) resolution continues to improve, making it important to understand the cellular basis for different MRI contrast mechanisms. Manganese-enhanced MRI (MEMRI) produces layer-specific contrast throughout the brain enabling in vivo visualization of cellular cytoarchitecture, particularly in the cerebellum. Due to the unique geometry of the cerebellum, especially near the midline, 2D MEMRI images can be acquired from a relatively thick slice by averaging through areas of uniform morphology and cytoarchitecture to produce very high-resolution visualization of sagittal planes. In such images, MEMRI hyperintensity is uniform in thickness throughout the anterior-posterior axis of sagittal sections and is centrally located in the cerebellar cortex. These signal features suggested that the Purkinje cell layer, which houses the cell bodies of the Purkinje cells and the Bergmann glia, is the source of hyperintensity. Despite this circumstantial evidence, the cellular source of MRI contrast has been difficult to define. In this study, we quantified the effects of selective ablation of Purkinje cells or Bergmann glia on cerebellar MEMRI signal to determine whether signal could be assigned to one cell type. We found that the Purkinje cells, not the Bergmann glia, are the primary of source of the enhancement in the Purkinje cell layer. This cell-ablation strategy should be useful for determining the cell specificity of other MRI contrast mechanisms.

Longitudinal manganese-enhanced magnetic resonance imaging of neural projections and activity

Manganese-enhanced magnetic resonance imaging (MEMRI) holds exceptional promise for preclinical studies of brain-wide physiology in awake-behaving animals. The objectives of this review are to update the current information regarding MEMRI and to inform new investigators as to its potential. Mn(II) is a powerful contrast agent for two main reasons: (1) high signal intensity at low doses; and (2) biological interactions, such as projection tracing and neural activity mapping via entry into electrically active neurons in the living brain. High-spin Mn(II) reduces the relaxation time of water protons: at Mn(II) concentrations typically encountered in MEMRI, robust hyperintensity is obtained without adverse effects. By selectively entering neurons through voltage-gated calcium channels, Mn(II) highlights active neurons. Safe doses may be repeated over weeks to allow for longitudinal imaging of brain-wide dynamics in the same individual across time. When delivered by stereotactic intracerebral injection, Mn(II) enters active neurons at the injection site and then travels inside axons for long distances, tracing neuronal projection anatomy. Rates of axonal transport within the brain were measured for the first time in "time-lapse" MEMRI. When delivered systemically, Mn(II) enters active neurons throughout the brain via voltage-sensitive calcium channels and clears slowly. Thus behavior can be monitored during Mn(II) uptake and hyperintense signals due to Mn(II) uptake captured retrospectively, allowing pairing of behavior with neural activity maps for the first time. Here we review critical information gained from MEMRI projection mapping about human neuropsychological disorders. We then discuss results from neural activity mapping from systemic Mn(II) imaged longitudinally that have illuminated development of the tonotopic map in the inferior colliculus as well as brain-wide responses to acute threat and how it evolves over time. MEMRI posed specific challenges for image data analysis that have recently been transcended. We predict a bright future for longitudinal MEMRI in pursuit of solutions to the brain-behavior mystery.

Cobalt Neurotoxicity: Transcriptional Effect of Elevated Cobalt Blood Levels in the Rodent Brain

Metal-on-metal (MoM) hip implants made of cobalt chromium (CoCr) alloy have shown early failure compared with other bearing materials. A consequence of the abnormal wear produced by these prostheses is elevated levels of cobalt in the blood of patients, which can lead to systemic conditions involving cardiac and neurological symptoms. In order to better understand the implications for patients with these implants, we carried out metal content and RNA-Seq analysis of excised tissue from rats treated intraperitonially for 28 days with low concentrations of cobalt. Cobalt blood levels in dosed rats were found to be similar to those seen in some patients with MoM implants (range: 4–38 μg/L Co in blood). Significant accumulation of cobalt was measured in a range of tissues including kidney, liver, and heart, but also in brain tissue. RNA-Seq analysis of neural tissue revealed that exposure to cobalt induces a transcriptional response in the prefrontal cortex (pref. cortex), cerebellum, and hippocampus. Many of the most up- and downregulated genes appear to correspond to choroid plexus transcripts. These results indicate that the choroid plexus could be the brain tissue most affected by cobalt. More specifically, the differentially expressed genes show a disruption of steroidogenesis and lipid metabolism. Several other transcripts also demonstrate that cobalt induces an immune response. In summary, cobalt exposure induces alterations in the brain transcriptome, more specifically, the choroid plexus, which is in direct contact with neurotoxicants at the blood–cerebrospinal fluid barrier.

Zwitterion-Coated Ultrasmall MnO Nanoparticles Enable Highly Sensitive T1-Weighted Contrast-Enhanced Brain Imaging

Manganese oxide nanoparticles (NPs) have attracted increasing attention recently as contrast agents (CAs) for magnetic resonance imaging (MRI). However, the clinical translation and popularization of conventional MnO NPs are hampered by their relatively poor imaging performance. Herein, we report the construction of ultrasmall MnO NPs (USMnO) via a one-pot synthetic approach that show a much better capability of T1-weighted contrast enhancement for MRI (r1 = 15.6 ± 0.4 mM-1 s-1 at 0.5 T) than MnCl2 and conventional large-sized MnO NPs (MnO-22). These USMnO are further coated with zwitterionic dopamine sulfonate (ZDS) molecules, which improves their biocompatibility and prevents nonspecific binding of serum albumins. Interestingly, USMnO@ZDS are capable of passing through the blood-brain barrier (BBB), which enables the acquisition of clear images showing brain anatomic structures with T1-weighted contrast-enhanced MRI. Therefore, our USMnO@ZDS could be used as a promising MRI CA for the flexible and accurate diagnosis of brain diseases, which is also instructive for the construction of manganese-based CA with a high MRI performance.

Evolution of brain-wide activity in the awake behaving mouse after acute fear by longitudinal manganese-enhanced MRI

Life threatening fear after a single exposure evolves in a subset of vulnerable individuals to anxiety, which may persist for their lifetime. Yet neither the whole brain's response to innate acute fear nor how brain activity evolves over time is known. Sustained neuronal activity may be a factor in the development of a persistent fear response. We couple two experimental protocols to provoke acute fear leading to prolonged fear: Predator stress (PS), a naturalistic approach to induce fear in rodents; and Serotonin transporter knockout mouse (SERT-KO) that responds to PS with sustained defensive behavior. Behavior was monitored before, during and at short and long times after PS in wild type (WT) and SERT-KO mice. Both genotypes responded to PS with defensive behavior. SERT-KO retained defensive behavior for 23 days, while WT mice returned to baseline exploratory behavior by 9 days. Thus, differences in neural activity between WT and SERT-KO 9 days after PS identifies neural correlates of persistent defensive behavior, in mice. We used longitudinal manganese-enhanced magnetic resonance imaging (MEMRI) to identify brain-wide neural activity associated with different behaviors. Mn2+ accumulation in active neurons occurs in awake, behaving mice and is retrospectively imaged. Following the same two cohorts of mice, WT and SERT-KO, longitudinally allowed unbiased quantitative comparisons of brain-wide activity by statistical parametric mapping (SPM). During natural behavior in WT, only low levels of activity-induced Mn2+-accumulation were detected, while much more accumulation appeared immediately after PS in both WT and SERT-KO, and evolved at 9 days to a new activity pattern (p < 0.0001, uncorr., T = 5.4). Patterns of accumulation differed between genotypes, with more regions of the brain and larger volumes within regions involved in SERT-KO than WT. A new computational segmentation analysis, using our InVivo Atlas based on a manganese-enhanced MR image of a living mouse, revealed dynamic changes in the volume of significantly enhanced voxels within each segment that differed between genotypes across 45 of 87 segmented regions. At Day 9 after PS, the striatum and ventral pallidum were active in both genotypes but more so in the SERT-KO. SERT-KO also displayed sustained or increased volume of Mn2+ accumulations between Post-Fear and Day 9 in eight segments where activity was decreased or silenced in WT. C-fos staining, an alternative neural activity marker, of brains from the same mice fixed at conclusion of imaging sessions confirmed that MEMRI detected active neurons. Intensity measurements in 12 regions of interest (ROIs) supported the SPM results. Between group comparisons by SPM and of ROI measurements identified specific regions differing between time points and genotypes. We report brain-wide activity in response to a single exposure of acute fear, and, for the first time, its evolution to new activity patterns over time in individuals vulnerable to persistent fear. Our results show multiple regions with dynamic changes in neural activity and that the balance of activity between segments is disordered in the SERT-KO. Thus, longitudinal MEMRI represents a powerful approach to discover how brain-wide activity evolves from the natural state either after an experience or during a disease process.

Longitudinal MEMRI analysis of brain phenotypes in a mouse model of Niemann-Pick Type C disease

Niemann-Pick Type C (NPC) is a rare genetic disorder characterized by progressive cell death in various tissues, particularly in the cerebellar Purkinje cells, with no known cure. Mouse models for human NPC have been generated and characterized histologically, behaviorally, and using longitudinal magnetic resonance imaging (MRI). Previous imaging studies revealed significant brain volume differences between mutant and wild-type animals, but stopped short of making volumetric comparisons of the cerebellar sub-regions. In this study, we present longitudinal manganese-enhanced MRI (MEMRI) data from cohorts of wild-type, heterozygote carrier, and homozygote mutant NPC mice, as well as deformation-based morphometry (DBM) driven brain volume comparisons across genotypes, including the cerebellar cortex, white matter, and nuclei. We also present the first comparisons of MEMRI signal intensities, reflecting brain and cerebellum sub-regional Mn²⁺-uptake over time and across genotypes.

Multivariate MR biomarkers better predict cognitive dysfunction in mouse models of Alzheimer's disease

To understand multifactorial conditions such as Alzheimer's disease (AD) we need brain signatures that predict the impact of multiple pathologies and their interactions. To help uncover the relationships between pathology affected brain circuits and cognitive markers we have used mouse models that represent, at least in part, the complex interactions altered in AD, while being raised in uniform environments and with known genotype alterations. In particular, we aimed to understand the relationship between vulnerable brain circuits and memory deficits measured in the Morris water maze, and we tested several predictive modeling approaches. We used in vivo manganese enhanced MRI traditional voxel based analyses to reveal regional differences in volume (morphometry), signal intensity (activity), and magnetic susceptibility (iron deposition, demyelination). These regions included hippocampus, olfactory areas, entorhinal cortex and cerebellum, as well as the frontal association area. The properties of these regions, extracted from each of the imaging markers, were used to predict spatial memory. We next used eigenanatomy, which reduces dimensionality to produce sets of regions that explain the variance in the data. For each imaging marker, eigenanatomy revealed networks underpinning a range of cognitive functions including memory, motor function, and associative learning, allowing the detection of associations between context, location, and responses. Finally, the integration of multivariate markers in a supervised sparse canonical correlation approach outperformed single predictor models and had significant correlates to spatial memory. Among a priori selected regions, expected to play a role in memory dysfunction, the fornix also provided good predictors, raising the possibility of investigating how disease propagation within brain networks leads to cognitive deterioration. Our cross-sectional results support that modeling approaches integrating multivariate imaging markers provide sensitive predictors of AD-like behaviors. Such strategies for mapping brain circuits responsible for behaviors may help in the future predict disease progression, or response to interventions.

Anatomy, Functionality, and Neuronal Connectivity with Manganese Radiotracers for Positron Emission Tomography

PURPOSE

Manganese ion has been extensively used as a magnetic resonance imaging (MRI) contrast agent in preclinical studies to assess tissue anatomy, function, and neuronal connectivity. Unfortunately, its use in human studies has been limited by cellular toxicity and the need to use a very low dose. The much higher sensitivity of positron emission tomography (PET) over MRI enables the use of lower concentrations of manganese, potentially expanding the methodology to humans.

PROCEDURES

PET tracers manganese-51 (Mn-51, t_1/2 = 46 min) and manganese-52 (Mn-52, t_1/2 = 5.6 days) were used in this study. The biodistribution of manganese in animals in the brain and other tissues was studied as well as the uptake in the pancreas after glucose stimulation as a functional assay. Finally, neuronal connectivity in the olfactory pathway following nasal administration of the divalent radioactive Mn-52 ([⁵²Mn]Mn²⁺) was imaged.

RESULTS

PET imaging with the divalent radioactive Mn-51 ([⁵¹Mn]Mn²⁺) and [⁵²Mn]Mn²⁺ in both rodents and monkeys demonstrates that the accumulation of activity in different organs is similar to that observed in rodent MRI studies following systemic administration. Furthermore, we demonstrated the ability of manganese to enter excitable cells. We followed activity-induced [⁵¹Mn]Mn²⁺ accumulation in the pancreas after glucose stimulation and showed that [⁵²Mn]Mn²⁺ can be used to trace neuronal connections analogous to manganese-enhanced MRI neuronal tracing studies.

CONCLUSIONS

The results were consistent with manganese-enhanced MRI studies, despite the much lower manganese concentration used for PET (100 mM Mn²⁺ for MRI compared to ~ 0.05 mM for PET). This indicates that uptake and transport mechanisms are comparable even at low PET doses. This helps establish the use of manganese-based radiotracers in both preclinical and clinical studies to assess anatomy, function, and connectivity.

Manganese Enhanced MRI for Use in Studying Neurodegenerative Diseases

MRI has been extensively used in neurodegenerative disorders, such as Alzheimer’s disease (AD), frontal-temporal dementia (FTD), mild cognitive impairment (MCI), Parkinson’s disease (PD), Huntington’s disease (HD) and amyotrophic lateral sclerosis (ALS). MRI is important for monitoring the neurodegenerative components in other diseases such as epilepsy, stroke and multiple sclerosis (MS). Manganese enhanced MRI (MEMRI) has been used in many preclinical studies to image anatomy and cytoarchitecture, to obtain functional information in areas of the brain and to study neuronal connections. This is due to Mn²⁺ ability to enter excitable cells through voltage gated calcium channels and be actively transported in an anterograde manner along axons and across synapses. The broad range of information obtained from MEMRI has led to the use of Mn²⁺ in many animal models of neurodegeneration which has supplied important insight into brain degeneration in preclinical studies. Here we provide a brief review of MEMRI use in neurodegenerative diseases and in diseases with neurodegenerative components in animal studies and discuss the potential translation of MEMRI to clinical use in the future.

Manganese-Enhanced Magnetic Resonance Imaging: Overview and Central Nervous System Applications With a Focus on Neurodegeneration

Manganese-enhanced magnetic resonance imaging (MEMRI) rose to prominence in the 1990s as a sensitive approach to high contrast imaging. Following the discovery of manganese conductance through calcium-permeable channels, MEMRI applications expanded to include functional imaging in the central nervous system (CNS) and other body systems. MEMRI has since been employed in the investigation of physiology in many animal models and in humans. Here, we review historical perspectives that follow the evolution of applied MRI research into MEMRI with particular focus on its potential toxicity. Furthermore, we discuss the more current in vivo investigative uses of MEMRI in CNS investigations and the brief but decorated clinical usage of chelated manganese compound mangafodipir in humans.

Transcranial manganese delivery for neuronal tract tracing using MEMRI

There has been a growing interest in the use of manganese-enhanced MRI (MEMRI) for neuronal tract tracing in mammals, especially in rodents. For this MEMRI application, manganese solutions are usually directly injected into specific brain regions. Recently it was reported that manganese ions can diffuse through intact rat skull. Here the local manganese concentrations in the brain tissue after transcranial manganese application were quantified and the effectiveness of tracing from the area under the skull where delivery occurred was determined. It was established that transcranially applied manganese yields brain tissue enhancement dependent on the location of application on the skull and that manganese that enters the brain transcranially can trace to deeper brain areas.

In vivo MEMRI characterization of brain metastases using a 3D Look-Locker T1-mapping sequence

Although MEMRI (Manganese Enhanced MRI) informations were obtained on primary tumors in small animals, MEMRI data on metastases are lacking. Thus, our goal was to determine if 3D Look-Locker T1 mapping was an efficient method to evaluate Mn ions transport in brain metastases in vivo. The high spatial resolution in 3D (156 × 156 × 218 μm) of the sequence enabled to detect metastases of 0.3 mm³. In parallel, the T1 quantitation enabled to distinguish three populations of MDA-MB-231 derived brain metastases after MnCl2 intravenous injection: one with a healthy blood-tumor barrier that did not internalize Mn²⁺ ions, and two others, which T1 shortened drastically by 54.2% or 24%. Subsequent scans of the mice, enabled by the fast acquisition (23 min), demonstrated that these T1 reached back their pre-injection values in 24 h. Contrarily to metastases, the T1 of U87-MG glioma remained 26.2% shorter for one week. In vitro results supported the involvement of the Transient Receptor Potential channels and the Calcium-Sensing Receptor in the uptake and efflux of Mn²⁺ ions, respectively. This study highlights the ability of the 3D Look-Locker T1 mapping sequence to study heterogeneities (i) amongst brain metastases and (ii) between metastases and glioma regarding Mn transport.

Manganese-enhanced MRI Offers Correlation with Severity of Spinal Cord Injury in Experimental Models

BACKGROUND

Spinal cord injuries (SCI) are clinically challenging, because neural regeneration after cord damage is unknown. In SCI animal models, regeneration is evaluated histologically, requiring animal sacrifice. Noninvasive techniques are needed to detect longitudinal SCI changes.

OBJECTIVE

To compare manganese-enhanced magnetic resonance imaging (MRI [MEMRI]) in hemisection and transection of SCI rat models with diffusion tensor imaging (DTI) and histology.

METHODS

Rats underwent T9 spinal cord transection (n=6), hemisection (n=6), or laminectomy without SCI (controls, n=6). One-half of each group received lateral ventricle MnCl₂ injections 24 hours later. Conventional DTI or T1-weighted MRI was performed 84 hours post-surgery. MEMRI signal intensity ratio above and below the SCI level was calculated. Fractional anisotropy (FA) measurements were taken 1 cm rostral to the SCI. The percentage of FA change was calculated 10 mm rostral to the SCI epicenter, between FA at the dorsal column lesion normalized to a lateral area without FA change. Myelin load (percentage difference) among groups was analyzed by histology.

RESULTS

In transection and hemisection groups, mean MEMRI ratios were 0.62 and 0.87, respectively, versus 0.99 in controls (P<0.001 and P<0.001, respectively); mean FA decreases were 67.5% and 40.1%, respectively, compared with a 6.1% increase in controls (P=0.002 and P=0.019, respectively). Mean myelin load decreased by 38.8% (transection) and 51.8% (hemisection) compared to controls (99.1%) (P<0.001 and P<0.001, respectively). Pearson's correlation coefficients were -0.94 for MEMRI ratio and FA changes and 0.87 for MEMRI and myelin load.

CONCLUSION

MEMERI results correlated to SCI severity measured by FA and myelin load. MEMRI is a useful noninvasive tool to assess neuronal damage after SCI.

A New Approach Using Manganese-Enhanced MRI to Diagnose Acute Mesenteric Ischemia in a Rabbit Model: Initial Experience

PURPOSE

Manganese-enhanced MRI (MEMRI) has been applied to a wide range of biological and disease research. The purpose of the study was to use MEMRI to diagnose the acute mesenteric ischemia (AMI).

METHODS

The institutional experimental animal ethics committee approved this study. To optimize the dose of Mn(2+) infusion, a dose-dependent curve was obtained using Mn(2+)-enhanced T 1 map MRI by an intravenous infusion 2.5-20 nmol/g body weight (BW) of 50 nmol/L MnCl2. The eighteen animals were divided into control, sham-operated, and AMI groups. AMI models were performed by ligating the superior mesenteric artery (SMA). T 1 values were measured on T 1 maps in regions of the small intestinal wall and relaxation rate (ΔR 1) was calculated.

RESULTS

A nonlinear relationship between infused MnCl2 solution dose and increase in small intestinal wall ΔR 1 was observed. Control animal exhibited significant Mn(2+) clearance over time at the dose of 15 nmol/g BW. In the AMI model, ΔR 1 values (0.95 ± 0.13) in the small intestinal wall were significantly lower than in control group (2.05 ± 0.19) after Mn(2+) infusion (P < 0.01).

CONCLUSION

The data suggest that MEMRI shows potential as a diagnostic technique that is directly sensitive to the poor or absent perfusion in AMI.

Bone Marrow-Derived Cells as a Therapeutic Approach to Optic Nerve Diseases

Following optic nerve injury associated with acute or progressive diseases, retinal ganglion cells (RGCs) of adult mammals degenerate and undergo apoptosis. These diseases have limited therapeutic options, due to the low inherent capacity of RGCs to regenerate and due to the inhibitory milieu of the central nervous system. Among the numerous treatment approaches investigated to stimulate neuronal survival and axonal extension, cell transplantation emerges as a promising option. This review focuses on cell therapies with bone marrow mononuclear cells and bone marrow-derived mesenchymal stem cells, which have shown positive therapeutic effects in animal models of optic neuropathies. Different aspects of available preclinical studies are analyzed, including cell distribution, potential doses, routes of administration, and mechanisms of action. Finally, published and ongoing clinical trials are summarized.

Corticospinal Tract Tracing in the Marmoset with a Clinical Whole-Body 3T Scanner Using Manganese-Enhanced MRI

Manganese-enhanced MRI (MEMRI) has been described as a powerful tool to depict the architecture of neuronal circuits. In this study we investigated the potential use of in vivo MRI detection of manganese for tracing neuronal projections from the primary motor cortex (M1) in healthy marmosets (Callithrix Jacchus). We determined the optimal dose of manganese chloride (MnCl2) among 800, 400, 40 and 8 nmol that led to manganese-induced hyperintensity furthest from the injection site, as specific to the corticospinal tract as possible, and that would not induce motor deficit. A commonly available 3T human clinical MRI scanner and human knee coil were used to follow hyperintensity in the corticospinal tract 24h after injection. A statistical parametric map of seven marmosets injected with the chosen dose, 8 nmol, showed the corticospinal tract and M1 connectivity with the basal ganglia, substantia nigra and thalamus. Safety was determined for the lowest dose that did not induce dexterity and grip strength deficit, and no behavioral effects could be seen in marmosets who received multiple injections of manganese one month apart. In conclusion, our study shows for the first time in marmosets, a reliable and reproducible way to perform longitudinal ME-MRI experiments to observe the integrity of the marmoset corticospinal tract on a clinical 3T MRI scanner.

Spatial memory training induces morphological changes detected by manganese-enhanced MRI in the hippocampal CA3 mossy fiber terminal zone

Hippocampal mossy fibers (MFs) can show plasticity of their axon terminal arbor consequent to learning a spatial memory task. Such plasticity is seen as translaminar sprouting from the stratum lucidum (SL) of CA3 into the stratum pyramidale (SP) and the stratum oriens (SO). However, the functional role of this presynaptic remodeling is still obscure. In vivo imaging that allows longitudinal observation of such remodeling could provide a deeper understanding of this presynaptic growth phenomenon as it occurs over time. Here we used manganese-enhanced magnetic resonance imaging (MEMRI), which shows a high-contrast area that co-localizes with the MFs. This technique was applied in the detection of learning-induced MF plasticity in two strains of rats. Quantitative analysis of a series of sections in the rostral dorsal hippocampus showed increases in the CA3a' area in MEMRI of trained Wistar rats consistent with the increased SO+SP area seen in the Timm's staining. MF plasticity was not seen in the trained Lister-Hooded rats in either MEMRI or in Timm's staining. This indicates the potential of MEMRI for revealing neuro-architectures and plasticity of the hippocampal MF system in vivo in longitudinal studies.

Monitoring dynamic alterations in calcium homeostasis by T1-mapping manganese-enhanced MRI (MEMRI) in the early stage of small intestinal ischemia-reperfusion injury

Manganese-enhanced MRI studies have proven to be useful in monitoring physiological activities associated with calcium ions (Ca(2+)) due to the paramagnetic property of the manganese ion (Mn(2+)), which makes it an excellent probe of Ca(2+) . In this study, we developed a method in which a Mn(2+)-enhanced T1 -map MRI could enable the monitoring of Ca(2+) influx during the early stages of intestinal ischemia-reperfusion (I/R) injury. The Mn(2+) infusion protocol was optimized by obtaining dose-dependent and time-course wash-out curves using a Mn(2+)-enhanced T1-map MRI of rabbit abdomens following an intravenous infusion of 50 mmol/l MnCl2 (5-10 nmol/g body weight (BW)). In the rabbit model of intestinal I/R injury, T1 values were derived from the T1 maps in the intestinal wall region and revealed a relationship between the dose of the infused MnCl2 and the intestinal wall relaxation time. Significant Mn(2+) clearance was also observed over time in control animals after the infusion of Mn(2+) at a dose of 10 nmol/g BW. This technique was also shown to be sensitive enough to monitor variations in calcium ion homeostasis in vivo after small intestinal I/R injury. The T1 values of the intestinal I/R group were significantly lower (P < 0.05) than that of the control group at 5, 10, and 15 min after Mn(2+) infusion. Our data suggest that MnCl2 has the potential to be an MRI contrast agent that can be effectively used to monitor changes in intracellular Ca(2+) homeostasis during the early stages of intestinal I/R injury.

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.

Laminar specific detection of APP induced neurodegeneration and recovery using MEMRI in an olfactory based Alzheimer's disease mouse model

Manganese enhanced MRI (MEMRI) was used to detect specific laminar changes in the olfactory bulb (OB) to follow the progression of amyloid precursor protein (APP)-induced neuronal pathology and its recovery in a reversible olfactory based Alzheimer's disease (AD) mouse model. Olfactory dysfunction is an early symptom of AD, which suggests that olfactory sensory neurons (OSNs) may be more sensitive to AD related factors than neurons in other brain areas. Previously a transgenic mouse model was established that causes degeneration of OSNs by overexpressing humanized APP (hAPP), which results in a disruption of the olfactory circuitry with changes in the glomerular structure. In the present work, OB volume and manganese enhancement of the glomerular layer in the OB were decreased in mutant mice. Turning off APP overexpression with doxycycline produced a significant increase in manganese enhancement of the glomerular layer after only 1week, and further recovery after 3weeks, while treatment with Aβ antibody produced modest improvement with MRI measurements. Thus, MEMRI enables a direct tracking of laminar specific neurodegeneration through a non-invasive in vivo measurement. The use of MRI will enable assessment of the ability of different pharmacological reagents to block olfactory neuronal loss and can serve as a unique in vivo screening tool to both identify potential therapeutics and test their efficacy.

Manganese enhanced magnetic resonance imaging (MEMRI): a powerful new imaging method to study tinnitus

Manganese enhanced magnetic resonance imaging (MEMRI) is a method used primarily in basic science experiments to advance the understanding of information processing in central nervous system pathways. With this mechanistic approach, manganese (Mn(2+)) acts as a calcium surrogate, whereby voltage-gated calcium channels allow for activity driven entry of Mn(2+) into neurons. The detection and quantification of neuronal activity via Mn(2+) accumulation is facilitated by "hemodynamic-independent contrast" using high resolution MRI scans. This review emphasizes initial efforts to-date in the development and application of MEMRI for evaluating tinnitus (the perception of sound in the absence of overt acoustic stimulation). Perspectives from leaders in the field highlight MEMRI related studies by comparing and contrasting this technique when tinnitus is induced by high-level noise exposure and salicylate administration. Together, these studies underscore the considerable potential of MEMRI for advancing the field of auditory neuroscience in general and tinnitus research in particular. Because of the technical and functional gaps that are filled by this method and the prospect that human studies are on the near horizon, MEMRI should be of considerable interest to the auditory research community. This article is part of a Special Issue entitled <Annual Reviews 2014>.

X-ray fluorescence imaging of the hippocampal formation after manganese exposure

Manganese (Mn) intoxication results in neurological conditions similar, but not identical, to idiopathic Parkinson's disease. While the mechanism(s) by which Mn exposure leads to neurotoxic effects remains unclear, studies by magnetic resonance imaging demonstrate a high Mn accumulation in the hippocampal formation (HPCf) of the brain. Metal quantification using this method is not possible. Using X-ray fluorescence imaging, we measured the distribution of Mn in the HPCf for a rodent model of chronic Mn exposure and quantitatively compared it with distributions of other biologically relevant metals. We found considerable increases in average Mn concentrations in all analyzed areas and we identified the dentate gyrus (DG) and the cornus ammonis 3 (CA3) layer as areas accumulating the highest Mn content (∼1.2 μg Mn per g tissue). The DG is significantly enriched with iron (Fe), while the CA3 layer has high zinc (Zn) content. Additionally, significant spatial correlations were found for Mn-Zn concentrations across the HPCf substructures and for Mn-Fe concentrations in the DG. Combined results support that at least two mechanisms may be responsible for Mn transport and/or storage in the brain, associated with either Fe or Zn. Subcellular resolution images of metal distribution in cells of the CA3 show diffuse Mn distributions consistent with Mn localization in both the cytoplasm and nucleus. Mn was not increased in localized intracellular Fe or copper accumulations. A consistent Mn-Zn correlation both at the tissue (40 μm × 40 μm) and cellular (0.3 μm × 0.3 μm) levels suggests that a Zn transport/storage mechanism in the HPCf is likely associated with Mn accumulation.

Deletion in the N-terminal half of olfactomedin 1 modifies its interaction with synaptic proteins and causes brain dystrophy and abnormal behavior in mice

Olfactomedin 1 (Olfm1) is a secreted glycoprotein that is preferentially expressed in neuronal tissues. Here we show that deletion of exons 4 and 5 from the Olfm1 gene, which encodes a 52 amino acid long region in the N-terminal part of the protein, increased neonatal death and reduced body weight of surviving homozygous mice. Magnetic resonance imaging analyses revealed reduced brain volume and attenuated size of white matter tracts such as the anterior commissure, corpus callosum, and optic nerve. Adult Olfm1 mutant mice demonstrated abnormal behavior in several tests including reduced marble digging, elevated plus maze test, nesting activity and latency on balance beam tests as compared with their wild-type littermates. The olfactory system was both structurally and functionally disturbed by the mutation in the Olfm1 gene as shown by functional magnetic resonance imaging analysis and a smell test. Deficiencies of the olfactory system may contribute to the neonatal death and loss of body weight of Olfm1 mutant. Shotgun proteomics revealed 59 candidate proteins that co-precipitated with wild-type or mutant Olfm1 proteins in postnatal day 1 brain. Olfm1-binding targets included GluR2, Cav2.1, teneurin-4 and Kidins220. Modified interaction of Olfm1 with binding targets led to an increase in intracellular Ca(2+) concentration and activation of ERK1/2, MEK1 and CaMKII in the hippocampus and olfactory bulb of Olfm1 mutant mice compared with their wild-type littermates. Excessive activation of the CaMKII and Ras-ERK pathways in the Olfm1 mutant olfactory bulb and hippocampus by elevated intracellular calcium may contribute to the abnormal behavior and olfactory activity of Olfm1 mutant mice.

Tau immunotherapy and imaging

Disappointing findings from recent phase III trials on amyloid-β (Aβ) immunotherapy for Alzheimer's disease (AD) have shifted the focus of such treatments to the tau protein. As tau pathology correlates better with the degree of dementia than Aβ plaque burden, it is a more attractive target once cognitive impairments are evident, while Aβ therapies may be better suited for the presymptomatic phase of the disease. Over 12 years ago, we initiated a tau immunotherapy program, seeking to alleviate the functional impairments associated with tau lesions in tauopathies. We have reported that various active and passive tau immunizations diminish tau pathology and improve function, including cognition, in different mouse models. Both extra- and intracellular pathways are likely involved. The antibodies may block the spread of tau pathology via microglial phagocytosis of the antibody-tau complex and facilitate lysosomal tau clearance in neurons after endosomal uptake. We have observed such antibody internalization following intracarotid injection in mice and in various culture models. These include brain slices and primary neurons from tangle mice as well as human neuroblastoma cell lines. Antibody targeting of different intracellular protein aggregates, including α-synuclein, Aβ and superoxide dismutase has been reported by others. Now, several laboratories have confirmed and extended our findings using various active and passive tau immunizations in different models, thereby clearly establishing the feasibility of this approach for clinical trials. We are also working on imaging approaches to monitor tau pathology, its consequences and the efficacy of treatments. Dire need exists for such diagnostic methods for tauopathies. Overall, therapies and diagnostic tools targeting tau pathology have a great potential for AD and other tauopathies.

Manganese-enhanced MRI of rat brain based on slow cerebral delivery of manganese(II) with silica-encapsulated Mn x Fe(1-x) O nanoparticles

In this work, we report a monodisperse bifunctional nanoparticle system, MIO@SiO2 -RITC, as an MRI contrast agent [core, manganese iron oxide (MIO); shell, amorphous silica conjugated with rhodamine B isothiocyanate (RITC)]. It was prepared by thermal decomposition and modified microemulsion methods. The nanoparticles with varying iron to manganese ratios displayed different saturated magnetizations and relaxivities. In vivo MRI of rats injected intravenously with MIO@SiO2-RITC nanoparticles exhibited enhancement of the T1 contrast in brain tissue, in particular a time-delayed enhancement in the hippocampus, pituitary gland, striatum and cerebellum. This is attributable to the gradual degradation of MIO@SiO2-RITC nanoparticles in the liver, resulting in the slow release of manganese(II) [Mn(II)] into the blood pool and, subsequently, accumulation in the brain tissue. Thus, T1-weighted contrast enhancement was clearly detected in the anatomic structure of the brain as time progressed. In addition, T2*-weighted images of the liver showed a gradual darkening effect. Here, we demonstrate the concept of the slow release of Mn(II) for neuroimaging. This new nanoparticle-based manganese contrast agent allows one simple intravenous injection (rather than multiple infusions) of Mn(II) precursor, and results in delineation of the detailed anatomic neuroarchitecture in MRI; hence, this provides the advantage of the long-term study of neural function.

3D printing of rat salivary glands: The submandibular-sublingual complex

The morphology and the functionality of the murid glandular complex, composed of the submandibular and sublingual salivary glands (SSC), were the object of several studies conducted mainly using magnetic resonance imaging (MRI). Using a 4.7 T scanner and a manganese-based contrast agent, we improved the signal-to-noise ratio of the SSC relating to the surrounding anatomical structures allowing to obtain high-contrast 3D images of the SSC. In the last few years, the large development in resin melting techniques opened the way for printing 3D objects starting from a 3D stack of images. Here, we demonstrate the feasibility of the 3D printing technique of soft tissues such as the SSC in the rat with the aim to improve the visualization of the organs. This approach is useful to preserve the real in vivo morphology of the SCC in living animals avoiding the anatomical shape changes due to the lack of relationships with the surrounding organs in case of extraction. It is also harmless, repeatable and can be applied to explore volumetric changes occurring during body growth, excretory duct obstruction, tumorigenesis and regeneration processes. 3D printing allows to obtain a solid object with the same shape of the organ of interest, which can be observed, freely rotated and manipulated. To increase the visibility of the details, it is possible to print the organs with a selected zoom factor, useful as in case of tiny organs in small mammalia. An immediate application of this technique is represented by educational classes.

Manganese-enhanced magnetic resonance imaging (MEMRI) reveals brain circuitry involved in responding to an acute novel stress in rats with a history of repeated social stress

Responses to acute stressors are determined in part by stress history. For example, a history of chronic stress results in facilitated responses to a novel stressor and this facilitation is considered to be adaptive. We previously demonstrated that repeated exposure of rats to the resident-intruder model of social stress results in the emergence of two subpopulations that are characterized by different coping responses to stress. The submissive subpopulation failed to show facilitation to a novel stressor and developed a passive strategy in the Porsolt forced swim test. Because a passive stress coping response has been implicated in the propensity to develop certain psychiatric disorders, understanding the unique circuitry engaged by exposure to a novel stressor in these subpopulations would advance our understanding of the etiology of stress-related pathology. An ex vivo functional imaging technique, manganese-enhanced magnetic resonance imaging (MEMRI), was used to identify and distinguish brain regions that are differentially activated by an acute swim stress (15 min) in rats with a history of social stress compared to controls. Specifically, Mn(2+) was administered intracerebroventricularly prior to swim stress and brains were later imaged ex vivo to reveal activated structures. When compared to controls, all rats with a history of social stress showed greater activation in specific striatal, hippocampal, hypothalamic, and midbrain regions. The submissive subpopulation of rats was further distinguished by significantly greater activation in amygdala, bed nucleus of the stria terminalis, and septum, suggesting that these regions may form a circuit mediating responses to novel stress in individuals that adopt passive coping strategies. The finding that different circuits are engaged by a novel stressor in the two subpopulations of rats exposed to social stress implicates a role for these circuits in determining individual strategies for responding to stressors. Finally, these data underscore the utility of ex vivo MEMRI to identify and distinguish circuits engaged in behavioral responses.

Regional specificity of manganese accumulation and clearance in the mouse brain: implications for manganese-enhanced MRI

Manganese-enhanced MRI has recently become a valuable tool for the assessment of in vivo functional cerebral activity in animal models. As a result of the toxicity of manganese at higher dosages, fractionated application schemes have been proposed to reduce the toxic side effects by using lower concentrations per injection. Here, we present data on regional-specific manganese accumulation during a fractionated application scheme over 8 days of 30 mg/kg MnCl2 , as well as on the clearance of manganese chloride over the course of several weeks after the termination of the whole application protocol supplying an accumulative dose of 240 mg/kg MnCl2 . Our data show most rapid accumulation in the superior and inferior colliculi, amygdala, bed nucleus of the stria terminalis, cornu ammonis of the hippocampus and globus pallidus. The data suggest that no ceiling effects occur in any region using the proposed application protocol. Therefore, a comparison of basal neuronal activity differences in different animal groups based on locally specific manganese accumulation is possible using fractionated application. Half-life times of manganese clearance varied between 5 and 7 days, and were longest in the periaqueductal gray, amygdala and entorhinal cortex. As the hippocampal formation shows one of the highest T1 -weighted signal intensities after manganese application, and manganese-induced memory impairment has been suggested, we assessed hippocampus-dependent learning as well as possible manganese-induced atrophy of the hippocampal volume. No interference of manganese application on learning was detected after 4 days of Mn(2+) application or 2 weeks after the application protocol. In addition, no volumetric changes induced by manganese application were found for the hippocampus at any of the measured time points. For longitudinal measurements (i.e. repeated manganese applications), a minimum of at least 8 weeks should be considered using the proposed protocol to allow for sufficient clearance of the paramagnetic ion from cerebral tissue.

X-ray fluorescence imaging: a new tool for studying manganese neurotoxicity

The neurotoxic effect of manganese (Mn) establishes itself in a condition known as manganism or Mn induced parkinsonism. While this condition was first diagnosed about 170 years ago, the mechanism of the neurotoxic action of Mn remains unknown. Moreover, the possibility that Mn exposure combined with other genetic and environmental factors can contribute to the development of Parkinson's disease has been discussed in the literature and several epidemiological studies have demonstrated a correlation between Mn exposure and an elevated risk of Parkinson's disease. Here, we introduce X-ray fluorescence imaging as a new quantitative tool for analysis of the Mn distribution in the brain with high spatial resolution. The animal model employed mimics deficits observed in affected human subjects. The obtained maps of Mn distribution in the brain demonstrate the highest Mn content in the globus pallidus, the thalamus, and the substantia nigra pars compacta. To test the hypothesis that Mn transport into/distribution within brain cells mimics that of other biologically relevant metal ions, such as iron, copper, or zinc, their distributions were compared. It was demonstrated that the Mn distribution does not follow the distributions of any of these metals in the brain. The majority of Mn in the brain was shown to occur in the mobile state, confirming the relevance of the chelation therapy currently used to treat Mn intoxication. In cells with accumulated Mn, it can cause neurotoxic action by affecting the mitochondrial respiratory chain. This can result in increased susceptibility of the neurons of the globus pallidus, thalamus, and substantia nigra pars compacta to various environmental or genetic insults. The obtained data is the first demonstration of Mn accumulation in the substantia nigra pars compacta, and thus, can represent a link between Mn exposure and its potential effects for development of Parkinson's disease.

New method of manganese-enhanced Magnetic Resonance Imaging (MEMRI) for rat brain research

Manganese (Mn(2+))-enhanced MRI (MEMRI) is known to provide insight into functional and anatomical biology. However, this method, which uses Mn(2+) as a MRI-detectable contrast agent, has drawbacks such as the toxicity to cells beyond a certain level of Mn(2+). In this study, we attempt to determine a new method of ICV administration, the optimal concentration of administered Mn(2+) and the optimal MEMRI acquisition time following administration. Male Sprague-Dawley rats were used in the following experimental sessions: (1) intracerebroventricular (ICV) cannula implantation in the region of the cisterna magna, (2) serial dilution of MnCl(2) (20-80 mM), (3) ICV administration of MnCl(2) through the cannula, and (4) T(1)-weighted MRI measurements. We confirmed that cannula implantation in the region of the cisterna magna was a new ICV injection method for the administration of a contrast agent. The optimal concentration for MEMRI was 20/50 mM/µl of MnCl(2). The MEMRI data acquired at different time points indicate that most signal enhancement is maintained during 14-48 h after contrast agent injection, and 24 h was the optimal time to acquire images of the rat brain. The present study offers optimized parameters for contrast agent injection that would be a good basis for studies using MEMRI to research the rat brain.

Hippocampal MRI and other structural biomarkers: experimental approach to epileptogenesis

The present review is devoted to application of MRI techniques to the epileptic brain and the search for potential biomarkers of epileptogenicity and/or epileptogenesis in rodents that could be translated to the clinic. Diffusion-weighted imaging reveals very early changes in water movements. T(2)-weighted hypersignal indicates edema or gliosis within brain regions and is most often used along with histological assessment of neuronal loss. (31)P magnetic resonance spectroscopy measures the energy reserve of the tissue while (1)H spectroscopy assesses neuronal loss and mitochondrial dysfunction. (13)C spectroscopy analyzes, separately, neuronal and astrocytic metabolism and interactions between the two cell types. Finally, diffusion tensor imaging and tractography have been applied to the study of plasticity and show a good coherence with circuit changes assessed by Timm staining. The potential of these techniques as reliable biomarkers of epileptogenesis is still disputed. At the moment, one study has provided a reliable temporal evolution of the T(2) signal, predicting epileptogenesis in 100% of the cases, and further imaging approaches based on the techniques described here are still needed to identify potential early imaging biomarkers of epileptogenicity and/or epileptogenesis.

Dose dependence and temporal evolution of the T1 relaxation time and MRI contrast in the rat brain after subcutaneous injection of manganese chloride

Divalent manganese ion (Mn(2+)) is a widely used T(1) contrast agent in manganese-enhanced MRI studies to visualize functional neural tracts and anatomy in the brain in vivo. In animal studies, Mn(2+) is administered at a dose that will maximize the contrast, while minimizing its toxic effects. In rodents, systemic administration of Mn(2+) via intravenous injection has been shown to create unique MRI contrast in the brain at a maximum dose of 175 mg kg(-1). However, intravenous administration of Mn(2+) results in faster bioelimination of excess Mn(2+) from the plasma due to a steep concentration gradient between plasma and bile. By contrast, following subcutaneous injection (LD(50) value = 320 mg kg(-1)), Mn(2+) is released slowly into the bloodstream, thus avoiding immediate hepatic elimination resulting in prolonged accumulation of Mn(2+) in the brain via the choroid plexus than that obtained via intravenous administration. The goal of this study was to investigate MRI dose response of Mn(2+) in rat brain following subcutaneous administration of Mn(2+). Dose dependence and temporal dynamics of Mn(2+) after subcutaneous injection can prove useful for longitudinal in vivo studies that require brain enhancement to persist for a long period of time to visualize neuroarchitecture like in neurodegenerative disease studies.

Quantitative assessment of central nervous system disorder induced by prenatal X-ray exposure using diffusion and manganese-enhanced MRI

Prenatal radiation exposure induces various central nervous system (CNS) disorders depending on the dose, affected region and gestation period. The goal of this study was to assess noninvasively a CNS development disorder induced by prenatal X-ray exposure using quantitative manganese-enhanced MRI (MEMRI) as well as apparent diffusion coefficient (ADC) and transverse relaxation time (T(2)) maps in comparison with immunohistological staining. The changes in ΔR(1) (increase in the longitudinal relaxation rate (R(1)) from before and after MnCl(2) administration.) induced by the Mn(2+) contrast agent were evaluated in the CNS of normal and prenatally irradiated rats. ADC and T(2) were also compared with the histological results obtained using hematoxylin and eosin (to estimate cell density), activated caspase-3 (apoptotic cells) and glial fibrillary acidic protein (proliferation of astrocytes/astroglia). We found the following: (i) the decreased Mn(2+) uptake (indicated by a smaller ΔR(1)) for radiation-exposed rats was predominantly correlated with a decrease in cell viability (apoptotic cytopathogenicity) and CNS cell density after prenatal radiation exposure; (ii) the longer T(2) and ADC were associated with a decrease in CNS cell density and apoptotic alteration after radiation exposure. In addition to the slight proliferation of astroglia (+58%), there was a substantial decrease in cell density (-78%) and an excessive increase in apoptotic cells (+613%) in our prenatal radiation exposure model. The results suggest that MEMRI in the prenatal X-ray exposure model predominantly reflected the decrease in cell density and viability rather than the proliferation of astroglia. In conclusion, quantitative MEMRI with ADC/T(2) mapping provides objective information for the in vivo assessment of cellular level alterations by prenatal radiation exposure, and has the potential to be used as a standard approach for the evaluation of the cellular damage of radiotherapy.

Quantitative measurement of changes in calcium channel activity in vivo utilizing dynamic manganese-enhanced MRI (dMEMRI)

The ability of manganese ions (Mn(2+)) to enter cells through calcium ion (Ca(2+)) channels has been used for depolarization dependent brain functional imaging with manganese-enhanced MRI (MEMRI). The purpose of this study was to quantify changes to Mn(2+) uptake in rat brain using a dynamic manganese-enhanced MRI (dMEMRI) scanning protocol with the Patlak and Logan graphical analysis methods. The graphical analysis was based on a three-compartment model describing the tissue and plasma concentration of Mn. Mn(2+) uptake was characterized by the total distribution volume of manganese (Mn) inside tissue (V(T)) and the unidirectional influx constant of Mn(2+) from plasma to tissue (K(i)). The measurements were performed on the anterior (APit) and posterior (PPit) parts of the pituitary gland, a region with an incomplete blood brain barrier. Modulation of Ca(2+) channel activity was performed by administration of the stimulant glutamate and the inhibitor verapamil. It was found that the APit and PPit showed different Mn(2+) uptake characteristics. While the influx of Mn(2+) into the PPit was reversible, Mn(2+) was found to be irreversibly trapped in the APit during the course of the experiment. In the PPit, an increase of Mn(2+) uptake led to an increase in V(T) (from 2.8±0.3 ml/cm(3) to 4.6±1.2 ml/cm(3)) while a decrease of Mn(2+) uptake corresponded to a decrease in V(T) (from 2.8±0.3 ml/cm(3) to 1.4±0.3 ml/cm(3)). In the APit, an increase of Mn(2+) uptake led to an increase in K(i) (from 0.034±0.009 min(-1) to 0.049±0.012 min(-1)) while a decrease of Mn(2+) uptake corresponded to a decrease in K(i) (from 0.034±0.009 min(-1) to 0.019±0.003 min(-1)). This work demonstrates that graphical analysis applied to dMEMRI data can quantitatively measure changes to Mn(2+) uptake following modulation of neural activity.

Microcoil-based MR phase imaging and manganese enhanced microscopy of glial tumor neurospheres with direct optical correlation

Susceptibility differences among tissues were recently used for highlighting complementary contrast in MRI different from the conventional T(1), T(2), or spin density contrasts. This method, based on the signal phase, previously showed improved image contrast of human or rodent neuroarchitecture in vivo, although direct MR phase imaging of cellular architecture was not available until recently. In this study, we present for the first time the ability of microcoil-based phase MRI to resolve the structure of human glioma neurospheres at significantly improved resolutions (10 × 10 μm(2)) with direct optical image correlation. The manganese chloride property to function as a T(1) contrast agent enabled a closer examination of cell physiology with MRI. Specifically the temporal changes of manganese chloride uptake, retention and release time within and from individual clusters were assessed. The optimal manganese chloride concentration for improved MR signal enhancement was determined while keeping the cellular viability unaffected. The presented results demonstrate the possibilities to reveal structural and functional observation of living glioblastoma human-derived cells. This was achieved through the combination of highly sensitive microcoils, high magnetic field, and methods designed to maximize contrast to noise ratio. The presented approach may provide a powerful multimodal tool that merges structural and functional information of submilimeter biological samples.

Regional cerebral metabolism in mouse under chronic manganese exposure: implications for manganism

Chronic manganese (Mn) exposure in rodents, non-human primates and humans has been linked to Parkinson's disease like condition known as Manganism. Mn being a cofactor for many enzymes in brain has been known to be accumulated in various regions differentially and thus exert toxic effect upon chronic overexposure. In present study, neuropathology of Manganism was investigated by evaluating regional neuronal and astroglial metabolism in mice under chronic Mn exposure. Male C57BL6 mice were treated with MnCl(2) (25 mg/kg, i.p.) for 21 days. Cerebral metabolism was studied by co-infusing [U-(13)C(6)]glucose and [2-(13)C]acetate, and monitoring (13)C labeling of amino acids in brain tissue extract using (1)H-[(13)C] and (13)C-[(1)H]-NMR spectroscopy. Glutamate, choline, N-acetyl aspartate and myo-inositol were found to be reduced in thalamus and hypothalamus indicating a loss in neuronal and astroglial cells due to Mn neurotoxicity. Reduced labeling of Glu(C4) from [U-(13)C(6)]glucose and [2-(13)C]acetate indicates an impairment of glucose oxidation by glutamatergic neurons and glutamate-glutamine neurotransmitter cycle in cortex, striatum, thalamus-hypothalamus and olfactory bulb with chronic Mn exposure. Additionally, reduced labeling of Gln(C4) from [2-(13)C]acetate indicates a decrease in acetate oxidation by astroglia in the same regions. However, GABAergic function was alleviated only in thalamus-hypothalamus. Our findings indicate that chronic Mn impairs excitatory (glutamatergic) function in the majority of regions of brain while inhibitory (GABAergic) activity is perturbed only in basal ganglia.

In vivo imaging of human breast cancer mouse model with high level expression of calcium sensing receptor at 3T

OBJECTIVES

To demonstrate that manganese can visualise calcium sensing receptor (CaSR)-expressing cells in a human breast cancer murine model, as assessed by clinical 3T magnetic resonance (MR).

METHODS

Human MDA-MB-231-Luc or MCF7-Luc breast cancer cells were orthotopically grown in NOD/SCID mice to a minimum mass of 5 mm. Mice were evaluated on T1-weighted sequences before and after intravenous injection of MnCl(2). To block the CaSR-activated Ca(2+) channels, verapamil was injected at the tumour site 5 min before Mn(2+) administration. CaSR expression in vivo was studied by immunohistochemistry.

RESULTS

Contrast enhancement was observed at the tumour periphery 10 min after Mn(2+) administration, and further increased up to 40 min. In verapamil-treated mice, no contrast enhancement was observed. CaSR was strongly expressed at the tumour periphery.

CONCLUSION

Manganese enhanced magnetic resonance imaging can visualise CaSR-expressing breast cancer cells in vivo, opening up possibilities for a new MR contrast agent.

KEY POINTS

• Manganese contrast agents helped demonstrate breast cancer cells in an animal model. • Enhancement was most marked in cells with high calcium sensing receptor expression. • Manganese uptake was related to the distribution of CaSR within the tumour. • Manganese MRI may become useful to investigate human breast cancer.

Statistical parametric mapping for effects of verapamil on olfactory connections of rat brain in vivo using manganese-enhanced MR imaging

PURPOSE

We investigated the effect of verapamil on the transport of manganese in the olfactory connections of rat brains in vivo using statistical parametric mapping and manganese-enhanced magnetic resonance (MR) imaging.

METHODS

We divided 12 7-week-old male Sprague-Dawley rats into 2 groups of six and injected 10 μL of saline into the right nasal cavities of the first group and 10 μL of verapamil (2.5 mg/mL) into the other group. Twenty minutes after the initial injection, we injected 10 μL of MnCl(2) (1 mol/L) into the right nasal cavities of both groups. We obtained serial T(1)-weighted MR images before administering the verapamil or saline and at 0.5, one, 24, 48, and 72 hours and 7 days after administering the MnCl(2), spatially normalized the MR images on the rat brain atlas, and analyzed the data using voxel-based statistical comparison.

RESULTS

Statistical parametric maps demonstrated the transport of manganese. Manganese ions created significant enhancement (t-score = 36.6) 24 hours after MnCl(2) administration in the group administered saline but not at the same time point in the group receiving verapamil. The extent of significantly enhanced regions peaked at 72 hours in both groups and both sides of the brain. The peak of extent in the right side brain in the group injected with saline was 70.2 mm(3) and in the group with verapamil, 92.4 mm(3). The extents in the left side were 64.0 mm(3) for the group with saline and 53.2 mm(3) for the group with verapamil.

CONCLUSION

We applied statistical parametric mapping using manganese-enhanced MR imaging to demonstrate in vivo the transport of manganese in the olfactory connections of rat brains with and without verapamil and found that verapamil did affect this transport.

Manganese-enhanced magnetic resonance imaging (MEMRI)

The use of manganese ions (Mn(2+)) as an MRI contrast agent was introduced over 20 years ago in studies of Mn(2+) toxicity in anesthetized rats (1). Manganese-enhanced MRI (MEMRI) evolved in the late nineties when Koretsky and associates pioneered the use of MEMRI for brain activity measurements (2) as well as neuronal tract tracing (3). Currently, MEMRI has three primary applications in biological systems: (1) contrast enhancement for anatomical detail, (2) activity-dependent assessment and (3) tracing of neuronal connections or tract tracing. MEMRI relies upon the following three main properties of Mn(2+): (1) it is a paramagnetic ion that shortens the spin lattice relaxation time constant (T(1)) of tissues, where it accumulates and hence functions as an excellent T(1) contrast agent; (2) it is a calcium (Ca(2+)) analog that can enter excitable cells, such as neurons and cardiac cells via voltage-gated Ca(2+) channels; and (3) once in the cells Mn(2+) can be transported along axons by microtubule-dependent axonal transport and can also cross synapses trans-synaptically to neighboring neurons. This chapter will emphasize the methodological approaches towards the use of MEMRI in biological systems.

Manganese-enhanced magnetic resonance imaging

Manganese-enhanced magnetic resonance imaging (MEMRI) relies on contrasts that are due to the shortening of the T (1) relaxation time of tissue water protons that become exposed to paramagnetic manganese ions. In experimental animals, the technique combines the high spatial resolution achievable by MRI with the biological information gathered by tissue-specific or functionally induced accumulations of manganese. After in vivo administration, manganese ions may enter cells via voltage-gated calcium channels. In the nervous system, manganese ions are actively transported along the axon. Based on these properties, MEMRI is increasingly used to delineate neuroanatomical structures, assess differences in functional brain activity, and unravel neuronal connectivities in both healthy animals and models of neurological disorders. Because of the cellular toxicity of manganese, a major challenge for a successful MEMRI study is to achieve the lowest possible dose for a particular biological question. Moreover, the interpretation of MEMRI findings requires a profound knowledge of the behavior of manganese in complex organ systems under physiological and pathological conditions. Starting with an overview of manganese pharmacokinetics and mechanisms of toxicity, this chapter covers experimental methods and protocols for applications in neuroscience.

Fractionated manganese injections: effects on MRI contrast enhancement and physiological measures in C57BL/6 mice

Manganese-enhanced MRI (MEMRI) is an increasingly used imaging method in animal research, which enables improved T(1)-weighted tissue contrast. Furthermore accumulation of manganese in activated neurons allows visualization of neuronal activity. However, at higher concentrations manganese (Mn2+) exhibits toxic side effects that interfere with the animals' behaviour and well-being. Therefore, when optimizing MEMRI protocols, a compromise has to be found between minimizing side effects and intensifying image contrast. Recently, a low concentrated fractionated Mn2+ application scheme has been proposed as a promising alternative. In this study, we investigated effects of different fractionated Mn2+ dosing schemes on vegetative, behavioural and endocrine markers, and MEMRI signal contrast in C57BL/6N mice. Measurements of the animals' well-being included telemetric monitoring of body temperature and locomotion, control of weight and observation of behavioural parameters during the time course of the injection protocols. Corticosterone levels after Mn2+ application served as endocrine marker of the stress response. We compared three MnCl2  x 4H2O application protocols: 3 times 60 mg/kg with an inter-injection interval of 48 h, six times 30 mg/kg with an inter-injection interval of 48 h, and 8 times 30 mg/kg with an inter-injection interval of 24 h (referred to as 3 x 60/48, 6 x 30/48 and 8 x 30/24, respectively). Both the 6 x 30/48 and the 8 x 30/24 protocols showed attenuated effects on animals' well-being as compared to the 3 x 60/48 scheme. Best MEMRI signal contrast was observed for the 8 x 30/24 protocol. Together, these results argue for a fractionated application scheme such as 30 mg/kg every 24 h for 8 days to provide sufficient MEMRI signal contrast while minimizing toxic side effects and distress.

Measurement of manganese content in various organs in rats with or without glucose stimulation

Our purpose in this study was to assess the manganese (Mn) content in various organs in rats with or without glucose stimulation in vivo and in vitro by using magnetic resonance imaging (MRI) and polarized Zeeman atomic absorption spectrophotometry (PZAAS), respectively. MRI studies were performed in 12 rats using a 1.5-T MRI system. The rats were injected intravenously with saline (6 ml/kg) (saline-stimulated group, n = 6) or glucose (2.34 g/kg) (glucose-stimulated group, n = 6). Ten minutes after saline or glucose administration, MnCl₂ (0.02 mmol/kg) was injected intravenously, followed by 6 MRI studies at 8-min intervals. After the last MRI study, rats were killed, and the Mn concentrations in various organs were measured using PZAAS. There was a discrepancy between in vivo and in vitro measurements, which appeared to be due to the partial volume effect and/or the contribution of extracellular Mn. The Mn concentration in the pancreas, normalized to that in the liver in the glucose-stimulated group, increased significantly compared to that in the saline-stimulated group, suggesting that the influx of Mn into β cells in the pancreas increased in response to glucose stimulation. This study suggested that the measurement of the change in the Mn concentration due to glucose stimulation using PZAAS was effective for evaluating β-cell function in the pancreas.

Responsive Mn(II) complexes for potential applications in diagnostic Magnetic Resonance Imaging

The investigation of new Mn(II)-based MRI/Molecular Imaging probes responsive to the enzyme tyrosinase for potential diagnostic applications is herein described. The expression of the enzyme tyrosinase, an oxidoreductase, is up-regulated in melanoma cancer cells. Three novel ligands (L(1), L(2) and L(3)) were designed as modified acyclic polyaminocarboxylate chelates by introducing an l-tyrosine residue in place of an aminoacetate unit. The corresponding Mn(II) complexes were fully characterised by (1)H NMR relaxometric techniques in aqueous media. The responsive activity towards the expression of tyrosinase was then assessed by monitoring the (1)H 1/T(1) relaxivity changes during incubation experiments in buffered solutions containing tyrosinase at different concentrations and in B16F10 melanoma cell homogenate. New insight on the mechanism of action of these systems was gained by measuring the magnetic field dependence of the relaxivity and ESR spectra of the incubated solutions. The systems developed showed responsive activity to tyrosinase with a relaxation enhancement spanning from 50% (MnL(1)) to 350% (MnL(3)) which augurs well for the development of diagnostic probes to detect melanoma cancer.

Detection of necrotic neural response in super-acute cerebral ischemia using activity-induced manganese-enhanced (AIM) MRI

Immediate and certain determination of the treatable area is important for choosing risky treatments such as thrombolysis for brain ischemia, especially in the super-acute phase. Although it has been suggested that the mismatch between regions displaying 'large abnormal perfusion' and 'small abnormal diffusion' indicates a treatable area on an MRI, it has also been reported that the mismatch region is an imperfect approximation of the treatable region named the 'penumbra'. Manganese accumulation reflecting calcium influx into cells was reported previously in a middle cerebral artery occlusion (MCAO) model using activity-induced manganese-enhanced (AIM) MRI. However, in the super-acute phase, there have been no reports about mismatches between areas showing changes to the apparent diffusion coefficient (ADC) and regions that are enhanced in AIM MRI. It is expected that the AIM signal can be enhanced immediately after cerebral ischemia in the necrotic core region due to calcium influx. In this study, a remote embolic rat model, created using titanium-oxide macrospheres, was used to observe necrotic neural responses in the super-acute phase after ischemia. In addition, images were evaluated by comparison between ADC, AIM MRI, and histology. The signal enhancement in AIM MRI was detected at 2 min after the cerebral infarction using a remote embolic method. The enhanced area on the AIM MRI was significantly smaller than that on the ADC map. The tissue degeneration highlighted by histological analysis corresponded more closely to the enhanced area on the AIM MRI than that on the ADC map. Thus, the manganese-enhanced region in brain ischemia might indicate 'necrotic' irreversible tissue that underwent calcium influx.

Progressive brain changes on serial manganese-enhanced MRI following traumatic brain injury in the rat

Traumatic brain injury (TBI) has a high incidence of long-term morbidity. Manganese-enhanced MRI (MEMRI) provides high contrast structural and functional detail of the brain in-vivo. The study utilized serial MEMRI scanning in the fluid percussion injury (FPI) rat's model to assess long-term changes in the brain following TBI. Rats underwent a left-sided craniotomy and a 3.5 atmosphere FPI pulse (n = 23) or sham procedure (n = 22). MEMRI acquisition was performed at baseline, 1 day, 1 month, and 6 months after FPI. Volume changes and MnCl(2) enhancement were measured blindly using region-of-interest analysis and the results analyzed with repeated measures MANOVA. Compared to the shams, FPI animals showed a progressive decrease in brain volume from 1 (right, p = 0.02; left, p = 0.008) to 6 months (right, p = 0.04; left, p = 0.006), with progression over time (F = 7.16, p = 0.00018). Similar changes were found in the cortex and the hippocampus. Conversely, the ventricular volume was increased at 1 (p = 0.02) and 6 months (p = 0.003), with progression over time (F = 7.27, p = 0.0001). There were no differences in thalamic or amygdalae volumes. The severity of the early neuromotor deficits and the T2 signal intensity of the subacute focal lesion were highly predictive of the severity of the long-term hippocampal decrease, and the former was also associated with the degree of neuronal sprouting. Differential MnCl(2) enhancement occurred only in the dentate gyrus at 1 month on the side of trauma (p = 0.04). Progressive functional and structural changes occur in specific brain regions post-FPI. The severity of the neuromotor deficit and focal signal changes on MRI subacutely post-injury are predictive of severity of these long-term neurodegenerative changes.

In vivo detection of individual glomeruli in the rodent olfactory bulb using manganese enhanced MRI

MRI contrast based on relaxation times, proton density, or signal phase have been applied to delineate neural structures in the brain. However, neural units such as cortical layers and columns have been difficult to identify using these methods. Manganese ion delivered either systemically or injected directly has been shown to accumulate specifically within cellular areas of the brain enabling the differentiation of layers within the hippocampus, cortex, cerebellum, and olfactory bulb in vivo. Here we show the ability to detect individual olfactory glomeruli using manganese enhanced MRI (MEMRI). Glomeruli are anatomically distinct structures ( approximately 150 microm in diameter) on the surface of the olfactory bulb that represent the first processing units for olfactory sensory information. Following systemic delivery of MnCl(2) we used 3D-MRI with 50 microm isotropic resolution to detect discrete spots of increased signal intensity between 100 and 200 microm in diameter in the glomerular layer of the rat olfactory bulb. Inflow effects of arterial blood and susceptibility effects of venous blood were suppressed and were evaluated by comparing the location of vessels in the bulb to areas of manganese enhancement using iron oxide to increase vessel contrast. These potential vascular effects did not explain the contrast detected. Nissl staining of individual glomeruli were also compared to MEMRI images from the same animals clearly demonstrating that many of the manganese enhanced regions corresponded to individual olfactory glomeruli. Thus, MEMRI can be used as a non-invasive means to detect olfactory glomeruli for longitudinal studies looking at neural plasticity during olfactory development or possible degeneration associated with disease.