August 22, 2016

Dead mouse tissue made transparent with solvent to reveal brain and nervous system

A new and versatile imaging technique enables researchers to trace the trajectories of whole nerve cells and provides extensive insights into the structure of neuronal networks.

The technique that shrinks the body and makes the tissue transparent could allow us to inspect human organs post mortem in greater detail than ever before

Lesions caused by traumatic brain damage, stroke and functional decline due to aging processes can disrupt the complex cellular network that constitutes the central nervous system, and lead to chronic pathologies, such as dementia, epilepsy and deleterious metabolic perturbations. “How exactly this happens is completely unknown,” says Dr. Ali Ertürk, who heads a research group at the Institute for Stroke and Dementia Research at the LMU Medical Center. Ertürk and his team previously developed and have now refined a novel imaging technique that allows them to visualize and monitor these structural alterations in neuronal networks. The new findings appear in the journal Nature Methods.

Nerve cells transmit electrical impulses over long distances along fibrous connections called axons, which extend from the cell body where the nucleus resides. Indeed, many neurons in the brainstem possess axons that project as far as the base of the spinal column. Thus damage to these axons can affect the function of parts of the central nervous system that are remote from the actual site of injury. The new imaging method is based on a clearing-and-shrinkage procedure that can render whole organs and organisms transparent, making – for instance – the full length of the rodent spinal cord accessible to optical imaging. Moreover, the technique is applicable down to the level of individual cells, which are labeled with fluorescent protein tags and can be visualized under the microscope by irradiating them with visible light. This enables researchers to map complex neuronal networks in rodents in 3D, a significant step in revealing the enigma behind the human brain.

Ali Ertürk of the Ludwig Maximilian University of Munich in Germany and his team have refined a technique called tissue clearing, so that the whole bodies of mice and rats can be studied in more detail than ever before. Other methods exist for making transparent rodents, but Ertürk’s technique also shrinks the body to around a third of its original size, making it possible to view the whole animal under a microscope, and subject it to detailed laser scanning for the first time.

This enabled the team to image all the nerve cell connections inside a mouse from head-to-toe, a feat never before accomplished, says Ertürk. “We imaged the complete central nervous system of mice, and you can track individual cells several centimeters long that reach from the brain right through to the tip of the spinal cord,” he says.

The technique involves using a solvent to wash out all of a dead animal’s body water, and much of its fat too, over three or four days. This leaves the remaining tissue, including the bones, transparent, enabling much clearer, crisper microscope images.

By taking many laser scans and putting these images together, the team generated a 3D projection of a mouse, with its nervous system illuminated by a glowing green protein. The projection allows researchers to travel virtually through the mouse, examining all its neural connections.

SOURCES - New Scientist, Ludwig Maximilian University of Munich in Germany, Youtube

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