Brain metal homeostasis is altered in neurodegenerative diseases and theconcentration, the localization and/or the chemical speciation of the elements can bemodified compared to healthy individuals. These changes are often specific to the brainregion affected by the neurodegenerative process. For example, iron concentration isincreased in the substantia nigra (SN) of Parkinson’s disease patients and iron redoxreactions might be involved in the pathogenesis. The identification of the molecularbasis behind metal dyshomeostasis in specific brain regions is the subject of intensiveresearch and chemical element imaging methods are particularly useful to address thisissue. Among the imaging modalities available, Synchrotron X-ray fluorescence (SXRF)and particle induced X-ray emission (PIXE) using focused micro-beams can inform aboutthe quantitative distribution of metals in specific brain regions. Micro-X-ray absorptionnear edge spectroscopy (XANES) can in addition identify the chemical species ofthe elements, in particular their oxidation state. However, in order to bring accurateinformation about metal changes in specific brain areas, these chemical imagingmethods must be correlated to brain tissue histology. We present a methodologyto perform chemical element quantitative mapping and speciation on well-identifiedbrain regions using correlative immunohistochemistry. We applied this methodologyto the study of an animal model of Parkinson’s disease, the 6-hydroxydopamine (6-OHDA) lesioned rat. Tyrosine hydroxylase immunohistochemical staining enabled toidentify the SN pars compacta (SNpc) and pars reticulata (SNpr) as well as the ventraltegmental area (VTA). Using PIXE we found that iron content was higher respectivelyin the SNpr > SNpc > VTA, but was not statistically significantly modified by 6-OHDA treatment. In addition, micro-SXRF revealed the higher manganese contentin the SNpc compared to the SNpr. Using micro-XANES we identified Fe oxidationstates 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 correlateimmunohistochemistry and chemical element imaging at the brain region level andthis protocol can now be widely applied to other studies of metal dyshomeostasisin neurology< Réduire