Investigation of prolonged hypobaric hypoxia-induced change in rat brain using T2 relaxometry and diffusion tensor imaging at 7T

Effect of Neurorepair for Motor Functional Recovery Enhanced by Total Saponins From Trillium tschonoskii Maxim. Treatment in a Rat Model of Focal Ischemia

Trillium tschonoskii Maxim. (TTM), is a perennial herb from Liliaceae, that has been widely used as a traditional Chinese medicine treating cephalgia and traumatic hemorrhage. The present work was designed to investigate whether the total saponins from Trillium tschonoskii Maxim. (TSTT) would promote brain remodeling and improve gait impairment in the chronic phase of ischemic stroke. A focal ischemic model of male Sprague-Dawley (SD) rats was established by permanent middle cerebral artery occlusion (MCAO). Six hours later, rats were intragastrically treated with TSTT (120, 60, and 30 mg/kg) and once daily up to day 30. The gait changes were assessed by the CatWalk-automated gait analysis system. The brain tissues injuries, cerebral perfusion and changes of axonal microstructures were detected by multimodal magnetic resonance imaging (MRI), followed by histological examinations. The axonal regeneration related signaling pathways including phosphatidylinositol 3-kinases (PI3K)/protein kinase B (AKT)/glycogen synthase kinase-3 (GSK-3)/collapsin response mediator protein-2 (CRMP-2) were measured by western blotting. TSTT treatment significantly improved gait impairment of rats. MRI analysis revealed that TSTT alleviated tissues injuries, significantly improved cerebral blood flow (CBF), enhanced microstructural integrity of axon and myelin sheath in the ipsilesional sensorimotor cortex and internal capsule. In parallel to MRI findings, TSTT preserved myelinated axons and promoted oligodendrogenesis. Specifically, TSTT interventions markedly up-regulated expression of phosphorylated GSK-3, accompanied by increased expression of phosphorylated PI3K, AKT, but reduced phosphorylated CRMP-2 expression. Taken together, our results suggested that TSTT facilitated brain remodeling. This correlated with improving CBF, encouraging reorganization of axonal microstructure, promoting oligodendrogenesis and activating PI3K/AKT/GSK-3/CRMP-2 signaling, thereby improving poststroke gait impairments.

Altered brain fluid management in a rat model of arterial hypertension

Background

Proper neuronal function is directly dependent on the composition, turnover, and amount of interstitial fluid that bathes the cells. Most of the interstitial fluid is likely to be derived from ion and water transport across the brain capillary endothelium, a process that may be altered in hypertension due to vascular pathologies as endothelial dysfunction and arterial remodelling. In the current study, we investigated the effects of hypertension on the brain for differences in the water homeostasis.

Methods

Magnetic resonance imaging (MRI) was performed on a 7T small animal MRI system on male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) of 10 months of age. The MRI protocol consisted of T2-weighted scans followed by quantitative apparent diffusion coefficient (ADC) mapping to measure volumes of different anatomical structures and water diffusion respectively. After MRI, we assessed the spatial distribution of aquaporin 4 expression around blood vessels.

Results

MRI analysis revealed a significant reduction in overall brain volume and remarkably higher cerebroventricular volume in SHR compared to WKY. Whole brain ADC, as well as ADC values of a number of specific anatomical structures, were significantly lower in hypertensive animals. Additionally, SHR exhibited higher brain parenchymal water content. Immunohistochemical analysis showed a profound expression of aquaporin 4 around blood vessels in both groups, with a significantly larger area of influence around arterioles. Evaluation of specific brain regions revealed a decrease in aquaporin 4 expression around capillaries in the corpus callosum of SHR.

Conclusion

These results indicate a shift in the brain water homeostasis of adult hypertensive rats.

A Multicenter Preclinical MRI Study: Definition of Rat Brain Relaxometry Reference Maps

Similarly to human population imaging, there are several well-founded motivations for animal population imaging, the most notable being the improvement of the validity of statistical results by pooling a sufficient number of animal data provided by different imaging centers. In this paper, we demonstrate the feasibility of such a multicenter animal study, sharing raw data from forty rats and processing pipelines between four imaging centers. As specific use case, we focused on T1 and T2 mapping of the healthy rat brain at 7T. We quantitatively report about the variability observed across two MR data providers and evaluate the influence of image processing steps on the final maps, using three fitting algorithms from three centers. Finally, to derive relaxation times from different brain areas, two multi-atlas segmentation pipelines from different centers were performed on two different platforms. Differences between the two data providers were 2.21% for T1 and 9.52% for T2. Differences between processing pipelines were 1.04% for T1 and 3.33% for T2. These maps, obtained in healthy conditions, may be used in the future as reference when exploring alterations in animal models of pathology.

Effects of total saponins from Trillium tschonoskii rhizome on grey and white matter injury evaluated by quantitative multiparametric MRI in a rat model of ischemic stroke

ETHNOPHARMACOLOGICAL RELEVANCE

Trillium tschonoskii rhizome (TTR), a medicinal herb, has been traditionally used to treat traumatic brain injury and headache in China. Although the potential neuroprotective efficacy of TTR has gained increasing interest, the pharmacological mechanism remains unclear. Steroid saponins are the main bioactive components of the herb.

AIM OF THE STUDY

To investigate the protective and repair-promoting effects of the total saponins from TTR (TSTT) on grey and white matter damages in a rat model of middle cerebral artery occlusion (MCAO) using magnetic resonance imaging (MRI) assay.

MATERIALS AND METHODS

Ischemic stroke was induced by MCAO. TSTT and Ginaton (positive control) were administered orally to rats 6h after stroke and daily thereafter. After 15 days of treatment, the survival rate of each group was calculated. We then conducted neurological deficit scores and beam walking test to access the neurological function after ischemic stroke. Subsequently, T2-weighted imaging (T2WI) and T2 relaxometry mapping were performed to measure infarct volume and grey and white matter integrity, respectively. Moreover, diffusion tensor imaging (DTI) was carried out to evaluate the grey and white matter microstructural damage. Additionally, arterial spin labelling (ASL) - cerebral blood flow (CBF) and magnetic resonance angiography (MRA) images provided dynamic information about vascular hemodynamic dysfunction after ischemic stroke. Finally, haematoxylin and eosin (HE) staining was carried out to evaluate the stroke-induced pathological changes in the brain.

RESULTS

The survival rate and neurological behavioural outcomes (Bederson scores and beam walking tests) were markedly ameliorated by TSTT (65mg/kg) treatment within 15 days after ischemic stroke. Moreover, T2WI and T2 relaxometry mapping showed that TSTT (65mg/kg) significantly reduced infarct volume and attenuated grey and white matter injury, respectively, which was confirmed by histopathological evaluation of brain tissue. The results obtained from DTI showed that TSTT (65mg/kg) not only significantly alleviated axonal damage and demyelination, but also promoted axonal remodelling and re-myelination. In addition, TSTT treatment also enhanced vascular signal density and increased CBF in rats after MCAO.

CONCLUSION

Our results suggested the potential protective and repair-promoting effects of TSTT on grey and white matter from damage induced by ischemia. This study provides a modern pharmacological basis for the application of TSTT in managing ischemic stroke.

Long-term sequelae of hippocampal lesions in patients with transient global amnesia: A multiparametric MRI study

BACKGROUND

MRI signal diffusion-weighted imaging (DWI) hyperintensity in the hippocampus in patients with transient global amnesia (TGA) are resolved within several days after the onset of TGA.

PURPOSE

To use multiparametric MRI to unravel the sequelae of TGA.

STUDY TYPE

A prospective longitudinal study.

POPULATION

Eight TGA patients.

FIELD STRENGTH/SEQUENCE

A 3.0T Siemens Tim Trio MRI scanner with T₁ -weighted MPRAGE, diffusion-weighted echo planar imaging, and multiecho gradient-recalled echo sequences.

ASSESSMENT

Brain MRI scanned within 72 hours, 2 weeks, and 3 months after onset of TGA, respectively. T₁ image hippocampus was first segmented into 12 subregions using FreeSurfer and registered to DWI to locate DWI lesion. Then a T₁ image with segmented hippocampus was registered to its corresponding apparent diffusion coefficient (ADC) map, fractional anisotropy (FA) map, and quantitative susceptibility map, respectively. Finally, the volume, water diffusion and anisotropy, and magnetic susceptibility of DWI lesion were analyzed.

STATISTICAL TESTS

A paired samples t-test was performed to detect measurement differences between three tests. Pearson correlation was used to assess the correlations between all measurements.

RESULTS

Hyperintensity was detected in the head, body, and caudate of CA1 and hippocampal tail. No significant changes existed in CA1/unit volume across the three timepoint measurements (all, P > 0.480). In Test 1, ratio ADC (DWI lesion / adjacent healthy, rADC) and ratio FA (rFA) decreased below, while ratio susceptibility increased above 1.0. In Test 2, all the episodes normalized around 1.0. In Test 3, rADC remained normalization, but rFA decreased and ratio susceptibility increased again. In Test 1 and Test 3 (vs. Test 2), decreased FA values were accompanied with lower axial diffusivity and/or higher radial diffusivity (all, P < 0.001). Moreover, rFA significantly correlated with ratio susceptibility in Test 3 (r = -0.665, P = 0.039).

DATA CONCLUSION

Microstructural sequelae in hippocampus were demonstrated, which indicates that ischemic lesions may be associated with TGA.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:1350-1358.

In vivo measurement of T1 and T2 relaxation times in awake pigeon and rat brains at 7T

PURPOSE

Establishment of regional longitudinal (T₁ ) and transverse (T₂ ) relaxation times in awake pigeons and rats at 7T field strength. Regional differences in relaxation times between species and between two different pigeon breeds (homing pigeons and Figurita pigeons) were investigated.

METHODS

T₁ and T₂ relaxation times were determined for nine functionally equivalent brain regions in awake pigeons and rats using a multiple spin-echo saturation recovery method with variable repetition time and a multi-slice/multi-echo sequence, respectively. Optimized head fixation and habituation protocols were applied to accustom animals to the scanning conditions and to minimize movement.

RESULTS

The habituation protocol successfully limited movement of the awake animals to a negligible minimum, allowing reliable measurement of T₁ and T₂ values within all regions of interest. Significant differences in relaxation times were found between rats and pigeons but not between different pigeon breeds.

CONCLUSION

The obtained T₁ and T₂ values for awake pigeons and rats and the optimized habituation protocol will augment future MRI studies with awake animals. The differences in relaxation times observed between species underline the importance of the acquisition of T₁ /T₂ values as reference points for specific experiments. Magn Reson Med 79:1090-1100, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Quantification and reproducibility assessment of the regional brain T2 relaxation in naïve rats at 7T

PURPOSE

To measure the reproducibility of T₂ relaxation and to determine the statistical power of T₂ mapping in the rat brain as a characteristic of the baseline performance of the T₂ relaxation as a potential biomarker of neurotoxicity.

MATERIALS AND METHODS

Multislice multiecho spin-echo imaging was utilized to obtain the quantitative T₂ maps in 138 naïve rats at 7T. Images were skull-stripped and coregistered to the common anatomical reference. A full anatomical segmentation mask, which included all major brain structures, was created using the same reference T₂ map. The overall variability map was also calculated from all T₂ maps and the areas with arbitrarily high variability (coefficient of variation >25%) were excluded from the full segmentation mask to produce a trimmed mask. T₂ maps were segmented using both these masks and statistical power analysis was conducted in all segmented areas.

RESULTS

The coefficient of variation of T₂ relaxation in different brain areas varied from 5.4% (cerebrospinal fluid) to 1.2% (cortex) when using a full segmentation mask. The use of a trimmed segmentation mask decreased the coefficient of variation in many areas, which ranged between 3.2% (inferior colliculi) and 1.2% (cortex) in this case. As revealed by statistical power analysis to detect 5% change with power of 0.8, the minimum number of observations needed for different areas ranged from 3 (cortex) to 8 (inferior colliculi) in the case of use of a trimmed segmentation mask.

CONCLUSION

T₂ relaxation is a very reproducible MRI parameter of the rat brain with high statistical power, which allows detecting very small changes in groups consisting of a minimal number of experimental animals.

LEVEL OF EVIDENCE

1 J. Magn. Reson. Imaging 2017;45:700-709.