What goes on inside a mouse's brain? Even though researchers have developed ways to make neurons fluoresce, they have a hard time observing them in an intact animal. Enter a new chemical cocktail named Scale. Researchers serendipitously discovered that a mixture of urea, glycerol, and soap makes synthetic membranes transparent. When they tried the mixture on a developing mouse fetus, they found that it removed all of the pigment from the cells, rendering them completely transparent (right). The technique, described online this week in Nature Neuroscience, allows scientists to see fluorescent neurons buried several millimeters in the brain (inset). But no need to worry about invisible mice creeping into your kitchen; Scale is too strong to use on a living animal.
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