IMAGING OF THICK SECTIONS OF NERVOUS-TISSUE WITH ENERGY-FILTERING TRANSMISSION ELECTRON-MICROSCOPY

Electron microscopy of nervous tissue requires on the one hand nanomet re resolution for the analysis of fine structures of nerve cell contac ts, for instance synaptic vesicles, synaptic membranes and associated organelles, On the other hand, the visualization of the three-dimensio nal organization of nervous tissue on the level of dendrites and neuri tes is essential for the understanding of neuronal integration and als o for a stereological evaluation of quantitative parameters such as si ze and shape of synaptic contact zones, number and distribution of syn aptic vesicles, organization of cytoskeleton and distribution of organ elles like mitochondria and endoplasmic reticulum. Therefore, it is ne cessary to have access to the fine structure and to the spatial organi zation within one sample. Energy-filtering transmission electron micro scopy (EFTEM) enables the imaging of sections up to 1 mu m thickness w ith a high resolution because the chromatic error due to inelastic sca ttering is avoided by selecting electrons within a restricted energy-l oss range for imaging, The contrast depends strongly upon the section thickness, the selected energy range and the composition of the sample , so that optimum imaging conditions can be found for each object, Dif ferent staining protocols enable either a high global contrast or a se lective staining of peculiar tissue properties, The three-dimensional organization can be visualized with stereopairs or with extended tilt series, which shows that characteristic structures as the synaptic jun ctions are detectable only within a narrow range of orientations to th e electron beam, This is especially important for quantitative approac hes with stereological tools which profit generally from the fact that a wide range of section thickness is available with EFTEM. EFTEM is t herefore a powerful tool for the imaging of thick sections of biologic al materials with attractive possibilities of contrast tuning and adva ntages for stereological quantifications. The main benefit is the rapi d and effective visualization of the three-dimensional organization of cells and tissues.