See-Through Body Parts

To learn how the brain works, some neuroscientists want to map nerve cell networks in the head and body. Last year, researchers at Stanford University made headlines when they rendered a whole mouse brain transparent to light and labeled its neurons with fluorescent dyes. Now, a team has optimized the chemical method used to make the brain see-through and applied it to a rodent’s entire body (Cell 2014, DOI: 10.1016/j.cell.2014.07.017). The original technique, dubbed Clarity, first converts tissue into a hydrogel and then pulls out light-blocking lipids from the gel with an electric field and detergent. Although this last step speeds up the process by forcing the lipids out, the electric field also heats the tissue, sometimes burning it. To improve Clarity, Viviana Gradinaru of Caltech and colleagues have developed a procedure called perfusion-assisted agent release in situ (PARS). In PARS, the scientists hook up tubing to a deceased rodent’s circulatory system. Over the course of a day or two, they convert the animal’s tissue to a hydrogel by pumping in polymerization ingredients such as acrylamide monomers and then applying gentle heat. To clear the lipids, the team flows the detergent sodium dodecyl sulfate through the rodent’s body for one to two weeks. Afterward, whole organs can be excised, stained, and imaged.