Study of manganese distribution and transport in the rodent brain using X-ray Fluorescence Imaging and spectroscopy.

摘要

Trace metals are important for proper function of the brain, serving as cofactors for a variety of proteins and enzymes. Furthermore, abnormally high/low trace metal content in the central nervous system has been associated with a variety of neurological disorders, for example Parkinson's disease. To properly understand the role played by trace metals in the development of neurological disorders, accurate information regarding the concentration and distribution of metal in the brain needs to be obtained.;Advancements in synchrotron sources, specifically in photon flux, focusing, and detection, have now opened a new avenue of research on metal distribution in tissue samples using x-ray fluorescence (XRF) imaging. The focus of this work is to apply XRF imaging as a suitable technique for measuring Mn content in thin tissue brain sections of a rat model of chronic Mn exposure, i.e. manganism. To date, other measurement techniques which are able to simultaneously provide distribution and content cannot do so for Mn due to small sampling volumes, insensitivity to total metal content, and/or limited resolution. Measurement of Mn in situ by XRF therefore provides new information regarding the physiological concentration and distribution which, in turn, may help to refine current models of neurotoxic action.;Results are compared to literature to validate the XRF imaging; we observe accumulation in structures of the basal ganglia, specifically the globus pallidus and thalamus, and in the hippocampal formation. Surprisingly, the substantia nigra compacta was identified as an additional target of Mn accumulation which is associated with motor dysfunction displayed in individuals suffering from Parkinson's disease. A strong Zn/Mn correlation consistently observed both for substructures of the basal ganglia and of the hippocampal formation suggesting a global, Zn-associated mechanism involved in Mn transport/sequestration. Since biological processes occur at the cellular level, further effort was directed towards XRF imaging at subcellular resolutions of pyramical cells of the cornus ammonis 3 layer of the hippocampal formation and dopaminergic cells of the substantia nigra compacta. Manganese accumulation was found to be the higher in the dopaminergic cells and a combined approach employing XRF imaging and x-ray absorption near edge spectroscopy demonstrated that Mn2+ and Mn3+ are both present in this structure. Together, data suggest that Mn accumulation results in aberrant function of the substantia nigra compacta, possibly through oxidative stress of the cell, leading to neurological symptoms observed in manganism. Furthermore, this observation could provide a link between Mn exposure and early onset of Parkinson's disease.