Ertürk, A. et al. Nat. Med. 18, 166–171 (2012).

Several chemical agents have been used to make tissues transparent and allow imaging deeper into living matter. Combining tissue clearance with light sheet–based illumination, for example, one can observe macroscopic specimens such as whole brains with microscopic resolution. In recent work, Ertürk and colleagues screened for the optimal clearing solution to visualize adult rodent tissue containing a large amount of lipids and a sturdy extracellular matrix such as the spinal cord. They settled on tetrahydrofuran, which rendered the tissue transparent by dehydration and lipid extraction without affecting the fluorescence signal of various fluorescent proteins and tracers. The group used the method to follow the trajectories of regenerating sensory axons in the unsectioned spinal cord, but the procedure can also be applied to other tissues.