Contrast Agents for Volumetric Analysis of Large, Complex Nervous Systems with X-rays

This joint research proposal of a chemist (Stefan Hecht) and a neuroscientist (Michael Brecht) aims at the development of novel contrast agents for large-scale X-ray based (microCT) analysis of neural structure. While the X-ray based assessment of bony structures in medical CT applications has long been standard practice, we currently witness an explosive extension of X-ray based techniques to the analysis of all kinds of biological (soft) tissues. These dramatic advances in X-ray based visualization have not yet been broadly applied in neuroscience. A major reason for the absence of microCT technique in the neurosciences is the lack of powerful dyes that allow the visualization of neural detail. We have developed a novel bimodal (X-ray/ fluorescence) neural tracer, DiI-CT, which can be visualized through microCT. The initial results from the application of DiI-CT are very encouraging and indicate that the dye can resolve the 3D structure of neural processes in optically inaccessible tissue. Inspired by this success, we plan to: (i) Further characterize DiI-CT. (ii) Develop improved DiI-CT derivatives. (iii) Apply DiI-CT. (iv) Develop and characterize a more universally applicable X-ray-dense labeling agent referred to as DAB-CT. (v) Explore a variety of other microCT staining strategies. Importantly, we expect that the novel dyes to be developed here will be broadly applicable and will operate well in large brains, post-mortem conditions and under conditions, where visual access is poor; we envision these features to open up areas of investigation, where current neuroscientific progress is limited.