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Researchers at Keio University’s medical school said they have succeeded in regenerating severed peripheral nerves in rats, potentially paving the way for more effective treatment of neurological disabilities associated with loss of sensory nerves through accidents or surgery.

Existing medical technology offers limited choices to mend peripheral nerves. One method is to transplant peripheral nerves from other parts of the body, but doctors say the scope of such transplants is limited.

The Keio research, led by lecturer Yasushi Nakao and professor Hideyuki Okano, essentially involves constructing a tiny artificial vein and growing nerve cells inside.

The researchers plan to present the findings at a national conference on the study of peripheral nerves in August in Tokyo.

Nerve damage, often caused by accidents and surgical procedures, sometimes results in sensory and motion disabilities.

Transplants to treat such disabilities have many constraints, including the type of nerves that are fit for the procedure.

To perform a nerve transplant, doctors have to remove peripheral nerves with less significant functions from healthy parts of a patient, often from the leg or elbow.

The procedure has its shortcomings, as it risks injuring healthy parts of the body and requires repeated surgery.

Extended to all parts the body, peripheral nerves consist of bundles of about 10,000 neurological fibers, which are part of Schwann cells, that are wrapped inside tiny membranes measuring just 1 mm in diameter.

Treating some types of injuries on peripheral nerves would require several such bundles, and doctors sometimes need to remove 50 cm of peripheral nerves for certain procedures.

The findings by the Keio team, if its safety and functional capability of regenerated nerves are proven, may pave the way for treating neurological disabilities without removing healthy nerves.

The Keio team created a tubular vein about 2 mm in diameter from a synthesized compound that can be absorbed by the human body in time and cultivated Schwann cells inside the artificial vein.

The team boosted nutrition-dispensing capabilities of Schwann cells by injecting a protein gene that promotes nerve growth.

The vein was then transplanted into the damaged peripheral nerves in a rat’s thigh. About 4,000 nerve fibers were found to have regenerated inside the vein in eight weeks.

The team found that the vein was connecting with the severed nerves in the rat’s thigh and that the nerves were regenerating outside the vein as well.

The researchers have yet to prove the regenerated nerves’ moving functions. They said that is on their future agenda.

Minoru Ueda, a Nagoya University professor who specializes in regenerative medicine, said the Keio team adopted a theoretically sound method, as regenerating nerves would grow only to a certain extent if nerve-growing protein genes are not used.

The Keio researchers succeeded in improving the length of the nerve decisively by making the nerve-growing substance diffuse efficiently, Ueda said.

Ueda said the technique has to clear many hurdles before a clinical trial. One problem, he said, is to connect the appropriate nerves to each other.

In addition, where to obtain Schwann cells can be a problem; the cells can be cultivated from a trace sample taken from humans, or can be cultivated from embryonic stem cells. Overcoming immunological rejection presents another problem.

The researchers also need to examine the safety of using nerve-growing genes.

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