Mapping Chemical Elements and Iron Oxidation States in the Substantia Nigra of 6-Hydroxydopamine Lesioned Rats Using Correlative Immunohistochemistry With Proton and Synchrotron Micro-Analysis
Résumé
Brain metal homeostasis is altered in neurodegenerative diseases and the
concentration, the localization and/or the chemical speciation of the elements can be
modified compared to healthy individuals. These changes are often specific to the brain
region affected by the neurodegenerative process. For example, iron concentration is
increased in the substantia nigra (SN) of Parkinson’s disease patients and iron redox
reactions might be involved in the pathogenesis. The identification of the molecular
basis behind metal dyshomeostasis in specific brain regions is the subject of intensive
research and chemical element imaging methods are particularly useful to address this
issue. Among the imaging modalities available, Synchrotron X-ray fluorescence (SXRF)
and particle induced X-ray emission (PIXE) using focused micro-beams can inform about
the quantitative distribution of metals in specific brain regions. Micro-X-ray absorption
near edge spectroscopy (XANES) can in addition identify the chemical species of
the elements, in particular their oxidation state. However, in order to bring accurate
information about metal changes in specific brain areas, these chemical imaging
methods must be correlated to brain tissue histology. We present a methodology
to perform chemical element quantitative mapping and speciation on well-identified
brain regions using correlative immunohistochemistry. We applied this methodology
to the study of an animal model of Parkinson’s disease, the 6-hydroxydopamine (6-
OHDA) lesioned rat. Tyrosine hydroxylase immunohistochemical staining enabled to
identify the SN pars compacta (SNpc) and pars reticulata (SNpr) as well as the ventral
tegmental area (VTA). Using PIXE we found that iron content was higher respectively
in the SNpr > SNpc > VTA, but was not statistically significantly modified by 6-
OHDA treatment. In addition, micro-SXRF revealed the higher manganese content
in the SNpc compared to the SNpr. Using micro-XANES we identified Fe oxidation
states in the SNpr and SNpc showing a spectral similarity comparable to ferritin for all brain regions and exposure conditions. This study illustrates the capability to correlate
immunohistochemistry and chemical element imaging at the brain region level and
this protocol can now be widely applied to other studies of metal dyshomeostasis
in neurology
Domaines
Physique [physics]
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