Sugar solution makes tissues see-through for analysis

Japanese researchers have developed a new sugar and water-based solution that turns tissues transparent in just three days, paving way for detailed imaging of biological structures like the brain.
Combined with fluorescence microscopy, this technique enabled researchers to obtain detailed images of a mouse brain at an unprecedented resolution without disrupting the shape and chemical nature of the samples.
Over the past few years, teams in the US and Japan have reported a number of techniques to make biological samples transparent, that have enabled researchers to look deep down into biological structures like the brain.
"However, these clearing techniques have limitations because they induce chemical and morphological damage to the sample and require time-consuming procedures," said Dr Takeshi Imai, who led the study.

SeeDB, an aqueous fructose solution that Imai developed with colleagues Drs Meng-Tsen Ke and Satoshi Fujimoto, overcomes these limitations.
Using SeeDB, the researchers were able to make mouse embryos and brains transparent in just three days, without damaging the fine structures of the samples, or the fluorescent dyes they had injected in them.

They could then visualise the neuronal circuitry inside a mouse brain, at the whole-brain scale, under a customised fluorescence microscope without making mechanical sections through the brain.
They describe the detailed wiring patterns of commissural fibers connecting the right and left hemispheres of the cerebral cortex, in three dimensions, for the first time.

Imai and colleagues report that they were also able to visualise in three dimensions the wiring of mitral cells in the olfactory bulb, which is involved the detection of smells, at single-fiber resolution.
"Because SeeDB is inexpensive, quick, easy and safe to use, and requires no special equipment, it will prove useful for a broad range of studies, including the study of neuronal circuits in human samples," the authors said.
The team from the RIKEN Center for Developmental biology reports their finding in Nature Neuroscience.