Narrow Results

Neurodegenerative disorders are accompanied by altered compositions of metals that may convey some information about the health and possibly metabolic state of neurons. Here we opted for PIXE technique to perform a spatially-resolved elemental analysis of intracellular space of individual neurons. Primarily, we measured element distribution within Purkinje cells (PC) of normal and Lurcher (Lc/+) mutant mice to detect any anomalies in concentrations of individual elements attributable to cell death. Lc/+ mutant mice provide an excellent animal model for time-course of excitotoxic cell death. PCs, some with autofluorescence, were scanned with a proton beam to record their X-ray emission and RBS spectra and to construct 2D-concentration maps of individual elements. PCs with auto-fluorescence, presumed to be either already dead or moribund, showed elevated concentrations of Cu, Fe, and Zn, when compared to healthy PCs. In conclusion, excitotoxic mode of death, as observed in the moribund PCs of Lc/+ cerebellum, may activate enzymatic processes, manifested as increased intracellular concentrations of Cu and Zn that are possibly constituents of some metalloenzyme complexes.

The simultaneously applied techniques of Particle Induced X-ray Emission (PIXE), Rutherford Backscattering Spectrometry (RBS) and Scanning Transmission Ion Microscopy (STIM), have been successful in mapping and quantifying trace elements during the progression of several human diseases, in particular those degenerative diseases which have a corresponding animal model. In atherosclerosis, iron has been shown to be present in increased concentrations at the early stage of lesion formation, and when the animal model has been kept anaemic, the artery wall shows a reduced uptake of iron and a delay in lesion formation compared with controls. In Parkinson's disease, there is also an increased concentration of iron in the substantia nigra region of the brain. Although the increase in bulk iron appears to lag behind the dopaminergic cell death, we have detected an increase in localized deposits of iron at the onset of cell death. These two results infer that iron may play a role in both diseases, perhaps through the mediation of free radicals. The induction of epilepsy through the injection of kainic acid has shown that the cell death is accompanied by an increase in calcium levels as early as one day after injection. The increase in calcium is consistent with activation of phospholipase A₂ and free radical damage.

The Oxford Scanning Proton Microprobe continues to be used in the field of trace element measurement in biological systems, exploiting the unique advantages of sensitive, quantitative trace element analysis using PIXE, high spatial resolution and the long penetrating power of MeV protons. This paper outlines a number of recent applications which highlight these advantages. These include: (a) Analysing the distribution of metals in the pupae of leaf-cutting ants to determine the storage sites and transport mechanism of metals used to harden the edges of the mandibles. (b) A study of the distribution of zinc in the retina of rats to determine the role of zinc in light and dark adaptation of the eye. (c) The analysis of crystals of proteins and other large organic molecules prepared for structure determination using x-ray diffraction. These often contain metal atoms, and the identity and concentration of the metal is an important diagnostic for determining the nature of the protein and the quality of the crystallisation. The crystals are normally small (~100μm) and so microPIXE is being used to characterise them. This technique has wide ranging applications, including qualitative and quantitative identification of metals in reaction centres, in active sites and in metal binding proteins, and of DNA or RNA bound to proteins.