Animals

Shrunken, See-Through Rodents Created

The feat paves the way for 3D models that could advance science and greatly reduce the number of lab animals used for study.

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Rodent bodies have just been shrunken and rendered fully transparent, according to a new study that indicates the process, called ultimate DISCO (uDISCO), could do the same to the brain of a dead human.

While this might seem like the plot of a B-horror film, the technology -- reported in the journal Nature Methods -- paves the way for understanding medical disorders ranging from cancer to Alzheimer's.

Senior author Ali Ertürk, who is a scientist at Ludwig Maximilians University of Munich's Institute for Stroke and Dementia Research, explained to Discovery News that the current "gold standard for more than a century" of studying biological tissue is to make thin sections of it and to study it under a microscope. Tumors, for example, are regularly examined this way.

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Photo: Mouse body before the process. Credit: Ali Ertürk

While this traditional method can answer some biological questions, it doesn't allow scientists to analyze whole systems, and particularly those -- like the nervous system -- that involve multiple areas within the body.

One obstacle is that tissue and related materials, such as fat and blood, obscure the view of organs and other internal parts. Anatomist Werner Spalteholz (1861–1940) developed a method for making human tissue transparent by drenching it in chemicals with similar light refraction properties as the tissue. This old method has become popular again in recent years due to its application in fluorescent laser scanning microscopy, which can label individual cells and molecules in the body for high-resolution imaging.

Even this more modern process is flawed, due to problems associated with the scattering of light and the fact that entire organs, much less whole bodies, still usually have to be cut into sections in order to fit under such machines for very detailed scans. The new tech, uDISCO, solves many of these problems.

Ertürk explained, "Transparency is achieved in our uDISCO method by first dehydrating the tissue (removing the water) and second, removing the lipids. The main reason for this is that water and lipids are the major cause of light scattering in the biological tissue. By eliminating them, we clear the path of imaging light."

Photo: A mouse undergoing the uDISCO process that renders the body transparent. Credit: Ali Ertürk

The researchers did this to the entire bodies of dead mice and managed to shrink them to one-third their usual size.

This "allowed for the first time laser-scanning imaging of a whole-mouse by fitting it in a small imaging chamber of the microscope, which could not be done before," Ertürk said. "Because of these laser scans of a whole mouse, we could follow individual neuronal and vascular connections from head to toe for the first time over several centimeters in animal models."

Ertürk likened the body shrinkage to fitting a balloon in a shirt pocket. In order for the balloon to fit into the limited-capacity pocket, its air has to be taken out. By removing bodily liquids and lipids from their specimens, the researchers ensure that the bodies of small mammals can be placed in their entirety under commercial microscopes.

Although the process shrunk the rodents in the study by up to 65%, it did not change the structural integrity of their brains at either the macroscopic (such as the cortex and hippocampus structures) or microscopic (for example, individual cells) scales. That's very promising for future research.

Ertürk said, "We expect that this method is easily applicable to small monkeys, even to a whole human brain in the near future."

Ingo Bechmann, professor of neuroimmunology at the University of Leipzig's Institute of Anatomy, said about the feat, "It is a revolution, an outstanding one!"

Bechmann explained that the revolution applies to "neuroanatomy, as it (uDISCO) eventually will allow us to see brain connectivity along with neurons in 3D. There are, however, many more applications." One, he said, is potentially showing how viral infections impact individuals at the cellular level.

Both he and Ertürk's team say that uDISCO's possibilities are nearly unlimited at this point. Ertürk and his colleagues are already collaborating with leading medical experts to study tumors, stem cells, inflammation, diabetes, stroke and Alzheimer's disease. They're also hoping to map the human brain.

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Ertürk said, "Now for the first time we have a powerful tool that can make the human brain transparent and reduce it to a size that will fit in an imaging microscope for mapping. However, how the post-mortem human brain neurons will be labeled with a fluorescent signal remains a major challenge to be solved beforehand."

The researchers also believe that there is an ethical benefit to using uDISCO. They say it will dramatically reduce the number of animals required for experimental research.

Currently an entire animal is usually sacrificed to study just one or a few of its bodily components. A neuroscientist might analyze just the brain of a dead rodent, for example, while an immunologist might only look at the animal's spleen or other immune-related organs. Since uDISCO paves the way for building whole body atlases for various biological systems such as nerves, vasculature and immune cells, researchers in the future will likely rely more on very detailed computerized models.

"This information will be available to everyone," said Ertürk, whose interest in imaging technologies was sparked by night stargazing, when he would wonder about galaxies like the Milky Way that would be visible one night but not on another due to clouds, lack of a full moon and other factors.

He added that to benefit from the envisioned models resulting from uDISCO, "One would just need to go to a website, choose the organ of their interest, and visualize various cellular systems within the individual organ or in the entire organism, if desired."

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