Dataset Information

The Neuromelanin-related T2* Contrast in Postmortem Human Substantia Nigra with 7T MRI.

ABSTRACT: High field magnetic resonance imaging (MRI)-based delineation of the substantia nigra (SN) and visualization of its inner cellular organization are promising methods for the evaluation of morphological changes associated with neurodegenerative diseases; however, corresponding MR contrasts must be matched and validated with quantitative histological information. Slices from two postmortem SN samples were imaged with a 7 Tesla (7T) MRI with T1 and T2* imaging protocols and then stained with Perl's Prussian blue, Kluver-Barrera, tyrosine hydroxylase, and calbindin immunohistochemistry in a serial manner. The association between T2* values and quantitative histology was investigated with a co-registration method that accounts for histology slice preparation. The ventral T2* hypointense layers between the SNr and the crus cerebri extended anteriorly to the posterior part of the crus cerebri, which demonstrates the difficulty with an MRI-based delineation of the SN. We found that the paramagnetic hypointense areas within the dorsolateral SN corresponded to clusters of neuromelanin (NM). These NM-rich zones were distinct from the hypointense ventromedial regions with high iron pigments. Nigral T2* imaging at 7T can reflect the density of NM-containing neurons as the metal-bound NM macromolecules may decrease T2* values and cause hypointense signalling in T2* imaging at 7T.

SUBMITTER: Lee JH

PROVIDER: S-EPMC5011647 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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The Neuromelanin-related T2* Contrast in Postmortem Human Substantia Nigra with 7T MRI.

Lee Jae-Hyeok JH Baek Sun-Yong SY Song YoungKyu Y Lim Sujeong S Lee Hansol H Nguyen Minh Phuong MP Kim Eun-Joo EJ Huh Gi Yeong GY Chun Se Young SY Cho HyungJoon H

Scientific reports 20160906

High field magnetic resonance imaging (MRI)-based delineation of the substantia nigra (SN) and visualization of its inner cellular organization are promising methods for the evaluation of morphological changes associated with neurodegenerative diseases; however, corresponding MR contrasts must be matched and validated with quantitative histological information. Slices from two postmortem SN samples were imaged with a 7 Tesla (7T) MRI with T1 and T2* imaging protocols and then stained with Perl's ...[more]

PMID: 27596274

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Project description:Improved markers for the progression of Parkinson's disease (PD) are required. Previous work has proven that iron dependent MRI scans can detect the largest Nigrosome (N1) within the substantia nigra (SN) pars compacta and changes in PD. Histopathological studies have shown that N1 is particularly affected in early PD whereas the other nigrosomes (N2-N5) and the surrounding iron-rich SN are affected later. In this study we aimed to determine whether MRI can detect the smaller nigrosomes (N2-N5) and whether graded signal alterations can be detected on T2*-weighted MRI at different disease stages consistent with histopathological changes. An observational prospective study was performed within the research imaging centre at the University of Nottingham, UK. Altogether 26 individuals with confirmed PD (median Hoehn&Yahr stage = 1, Unified PD Rating Scale [UPDRS] = 12.5) and 15 healthy controls participated. High resolution T2*weighted 7T MRI of the brain was performed and visibility of N1-N5 within the SN was qualitatively rated. Normalised T2*weighted signal intensities in manually segmented N1-N5 regions and iron-rich SN were calculated. We performed group comparisons and correlations with severity based on UPDRS. Qualitative measures were a nigrosome visibility score and a confidence score for identification. Quantitative measures were T2*weighted contrast of N1-5 and iron-rich SN relative to white matter. We found that visual assessment of the SN for N1-N5 revealed normal range visibility scores in 14 of 15 controls. N1 was identified with the highest confidence and visibility was in abnormal range in all 26 PD patients. The other nigrosomes were less well visible and less confidently identified. There was a larger PD induced signal reduction in all nigrosomes than in the iron-rich SN (median signal difference N1-5 PD compared to controls: 19.4% [IQR = 24%], iron-rich SN 11% [IQR = 24%, p = 0.017]). The largest PD induced signal reduction was in N1: 37.2% [IQR = 19%] which inversely correlated with UPDRS in PD (R2 = 0.19). All nigrosomes can be detected using 7T MRI, and PD induced T2*weighted signal reduction was greatest in the nigrosomes (especially N1). The graded T2*weighted signal alterations in the nigrosomes match previously described differential histopathological effects of PD. N1 was identified with the highest confidence and T2*weighted signal in N1 correlated with UPDRS confirming N1 as the most promising SN marker of PD pathology.

Project description:BackgroundNeuromelanin is a pigment with strong iron-chelating properties preferentially found in dopaminergic neurons of the substantia nigra pars compacta (SNpc). Parkinson's disease is characterized by pronounced, MRI-detectable neuromelanin loss, but the neuroprotective or neurotoxic role of neuromelanin remains debated. Histological studies have demonstrated neuromelanin increases with age, but this has not been confirmed in vivo, and there is uncertainty whether neuromelanin declines, stabilizes, or increases from middle age.MethodsThis study aimed to establish physiological changes of pigmentation of the SNpc using a pooled data set of neuromelanin-sensitive 3T MRI from 134 healthy individuals aged 5-83 years. Neuromelanin-related brightness (regional contrast to ratio) and calibrated hyperintense volumes were analyzed using linear and nonlinear regression models to characterize age effects. Laterality, sex, and subregional effects were also assessed.ResultsFor brightness, age effects were best described as a quadratic trajectory explaining 81.5% of the observed variance in the SNpc showing a strong increase from childhood to adolescence, with plateauing in middle age and a decline in older age. Similar but less pronounced effects were seen in hyperintense volumes. We also show an anterior-posterior gradient in SNpc contrast, larger normalized neuromelanin-rich volume in women > 47 years old, but no laterality effect.ConclusionsUsing optimized neuromelanin MRI in a life span sample, we demonstrate a strong age effect with inverted U-shaped SNpc pigmentation-related contrast from childhood to old age. This age trajectory of physiological SNpc pigmentation needs to be taken into account for diagnostic applications of depigmentation. The study also paves the way for systematic investigations of the mechanisms of neuromelanin in healthy and pathological brain development and aging. © 2018 International Parkinson and Movement Disorder Society.

Project description:This article gives a detailed description of a protocol using density gradient centrifugation for the enrichment of neuromelanin granules and synaptosomes from low amounts (?0.15g) of human substantia nigra pars compacta tissue. This has a great advantage compared to already existing methods as it allows for the first time (i) a combined enrichment of neuromelanin granules and synaptosomes and (ii) just minimal amounts of tissue necessary to enable donor specific analysis. Individual specimens were classified as control or diseased according to clinical evaluation and neuropathological examination. For the enrichment of synaptosomes and neuromelanin granules from the same tissue sample density gradient centrifugations using Percoll® and Iodixanol were performed. The purity of resulting fractions was checked by transmission electron microscopy. We were able to establish a reproducible and easy to handle protocol combining two different density gradient centrifugations: using an Iodixanol gradient neuromelanin granules were enriched and in parallel, from the same sample, a fraction of synaptosomes with high purity using a Percoll® gradient was obtained. Our subfractionation strategy will enable a subsequent in depth proteomic characterization of neurodegenerative processes in the substantia nigra pars compacta in patients with Parkinson's disease and dementia with Lewy bodies compared to appropriate controls.Key features of Parkinson's disease are the degeneration of dopaminergic neurons in the substantia nigra pars compacta, an associated loss of the brain pigment neuromelanin and a resulting impairment of the neuronal network. The accumulation of iron binding neuromelanin granules is age- and disease-dependent and disease specific alterations could affect the neuronal iron homeostasis leading to oxidative stress induced cell death. The focus of the described method is the analysis of neuromelanin granules as well as axonal cell-endings of nerve cells (synaptosomes) of individual donors (control and diseased). It is the basis for the identification of disease-relevant changes in the iron homeostasis and the generation of new insight into altered protein compositions or regulations which might lead to disturbed communications between nerve cells resulting in pathogenic processes.

Dataset Information

The Neuromelanin-related T2* Contrast in Postmortem Human Substantia Nigra with 7T MRI.

Publications

The Neuromelanin-related T2* Contrast in Postmortem Human Substantia Nigra with 7T MRI.

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