A major goal of the section of bioelectronics is the development of imaging methods which help the visualilzation of neuronal structures in the mouse brain. These techniques are applied to projects like neuronal network analysis in health and disease. A second area of research is the analysis of EEG data with the new nonlinear method “recurrence quantification analysis (RQA)”. Our latest technological development is a method called ultramicroscopy which allows the analysis of cm sized objects like whole brains with µm resolution:
Visualization of neuronal networks in the whole mouse brain by ultramicroscopy (glass brain).
It would be very helpful for the analysis of neuronal networks of the brain, if one could visualize these networks in 3 dimensions. Up to now this was only possible with limited resolution by sequential slicing and reconstruction of the brain. This time consuming attempt is easily hampered by artifacts as shrinkage and distortion induced by standard histological procedures.
To overcome these problems we developed a microscopy based on extreme darkfield illumination. This microscopy allows optical sectioning of whole mouse brains and was combined with an approach to clear fixed neuronal tissue: Mouse brains were made completely transparent by immersion in oil of the same refractive index as protein. By illuminating the brains with blue light (λ=488 nm), neurons labeled with GFP were visualized by fluorescence. This way we could detect single neurons in hippocampi inside whole brains.
By surface rendering the shape and position of hippocampi relative to the brain surface could be depicted. In complete excised hippocampi subcellular resolution was obtained by 3D reconstruction from several hundred optical sections. The dendritic trees of CA1 hippocampal neurons with dendrites and dendritic spines could be visualized.
Many proteins can be labelled in transgenic mice with genetically encoded fluorescent markers. Using these markers our approach will represent a high-throughput screening method for protein expression in 3 D. This expression can be monitored with µm resolution and should allow the elucidation of complex neuronal networks in the brain.
