Brain maturation of the adolescent rat cortex and striatum: changes in volume and myelination.

Longitudinal studies on brain pathology and assessment of therapeutic strategies rely on a fully mature adult brain to exclude confounds of cerebral developmental changes. Thus, knowledge about onset of adulthood is indispensable for discrimination of developmental phase and adulthood. We have performed a high-resolution longitudinal MRI study at 11.7T of male Wistar rats between 21days and six months of age, characterizing cerebral volume changes and tissue-specific myelination as a function of age. Cortical thickness reaches final value at 1month, while volume increases of cortex, striatum and whole brain end only after two months. Myelin accretion is pronounced until the end of the third postnatal month. After this time, continuing myelination increases in cortex are still seen on histological analysis but are no longer reliably detectable with diffusion-weighted MRI due to parallel tissue restructuring processes. In conclusion, cerebral development continues over the first three months of age. This is of relevance for future studies on brain disease models which should not start before the end of month 3 to exclude serious confounds of continuing tissue development.

A multi-modality platform to image stem cell graft survival in the naïve and stroke-damaged mouse brain.

Neural stem cell implantations have been extensively investigated for treatment of brain diseases such as stroke. In order to follow the localization and functional status of cells after implantation noninvasive imaging is essential. Therefore, we developed a comprehensive multi-modality platform for in vivo imaging of graft localization, density, and survival using 19F magnetic resonance imaging in combination with bioluminescence imaging. We quantitatively analyzed cell graft survival over the first 4 weeks after transplantation in both healthy and stroke-damaged mouse brain and correlated our findings of graft vitality with the host innate immune response. The multi-modality imaging platform will help to improve cell therapy also in context other than stroke and to gain indispensable information for clinical translation.

Vascular changes after stroke in the rat: a longitudinal study using optimized magnetic resonance imaging.

During stroke, the reduction of blood flow leads to undersupply of oxygen and nutrients and, finally, to cell death, but also to upregulation of pro-angiogenic molecules and vascular remodeling. However, the temporal profile of vascular changes after stroke is still poorly understood. Here, we optimized steady-state contrast-enhanced magnetic resonance imaging (SSCE MRI) and followed the dynamic changes in vascular architecture for up to 4 weeks after transient middle cerebral artery occlusion (MCAO) in rats. Using MRI diffusion measurements and the changes of transversal relaxation rates ΔR2 and ΔR2* after injection of a superparamagnetic contrast agent, SSCE MRI provided several hemodynamic parameters: relative cerebral blood volume (rCBV), rCBV in small vessels, microvascular density, and relative vessel size. Six rats underwent SSCE MRI before MCAO and at 7, 14, 21 and 28 days after surgery. 5-Bromo-2'deoxyuridine (BrdU) was injected between days 2 and 7 to label proliferating cells during this time. SSCE MRI depicted a decrease in microvessel density and an increase in vessel size in the ischemic striatum after stroke. A persistently decreased MRI vessel density was confirmed with histology at 28 days. BrdU + endothelial cells were found in regions close to the infarct indicating endothelial cell proliferation during the first week after MCAO; however, late-stage angiogenesis, as would be reflected by increased vessel density, was not detected. The optimized SSCE MRI protocol was used to follow spatio-temporal changes of important vessel characteristics, which may contribute to a better understanding of the role of angiogenesis at different stages after stroke.

In vivo tracking of human neural stem cells with 19F magnetic resonance imaging.

BACKGROUND: Magnetic resonance imaging (MRI) is a promising tool for monitoring stem cell-based therapy. Conventionally, cells loaded with ironoxide nanoparticles appear hypointense on MR images. However, the contrast generated by ironoxide labeled cells is neither specific due to ambiguous background nor quantitative. A strategy to overcome these drawbacks is (19)F MRI of cells labeled with perfluorocarbons. We show here for the first time that human neural stem cells (NSCs), a promising candidate for clinical translation of stem cell-based therapy of the brain, can be labeled with (19)F as well as detected and quantified in vitro and after brain implantation. METHODOLOGY/PRINCIPAL FINDINGS: Human NSCs were labeled with perfluoropolyether (PFPE). Labeling efficacy was assessed with (19)F MR spectroscopy, influence of the label on cell phenotypes studied by immunocytochemistry. For in vitro MRI, NSCs were suspended in gelatin at varying densities. For in vivo experiments, labeled NSCs were implanted into the striatum of mice. A decrease of cell viability was observed directly after incubation with PFPE, which re-normalized after 7 days in culture of the replated cells. No label-related changes in the numbers of Ki67, nestin, GFAP, or ßIII-tubulin+ cells were detected, both in vitro and on histological sections. We found that 1,000 NSCs were needed to accumulate in one image voxel to generate significant signal-to-noise ratio in vitro. A detection limit of ∼10,000 cells was found in vivo. The location and density of human cells (hunu+) on histological sections correlated well with observations in the (19)F MR images. CONCLUSION/SIGNIFICANCE: Our results show that NSCs can be efficiently labeled with (19)F with little effects on viability or proliferation and differentiation capacity. We show for the first time that (19)F MRI can be utilized for tracking human NSCs in brain implantation studies, which ultimately aim for restoring loss of function after acute and neurodegenerative disorders.