Nerve transplants wire themselves into host brains

Embryonic nerve cells transplanted into a recipient brain survive, wire themselves up and can even correct a metabolic disorder in vulnerable individuals, scientists have discovered.

Successful brain repair in the future will almost certainly depend upon the implantation, within the injured or diseased nervous system, of healthy cells that can replace those damaged by degeneration.

But the fate of these fresh cells, when added to an abnormal brain, and whether they can functionally wire themselves up to and support existing nerve circuits, is poorly understood.

Now scientists have proved that these cells can do this by using cell transplantation techniques to remedy an obesity-triggering metabolic disorder in mice.

Writing in Science, Harvard scientist Jeffrey Macklis and his colleagues transplanted into the obese mice, which lack the receptor in their brains for a satiety-signal called leptin, 15,000 nerve cells collected from 13 day old mouse embryos.

The cells, which also synthesised a glowing-green pigment to discriminate them from the hosts' brain cells, were implanted into a region of the brain known as the medial hypothalamus, which controls appetite.

Five months later, the researchers looked for signs that the donor neurones were still present in the brain and were speaking electrically with their host brain neighbours.

The implanted cells, they found, had wired themselves in and were functional. They also found that, compared with control animals and mice that had received grafts from other brain regions, the treated animals were 30% lighter and had more normal blood glucose measurements.

This, say the scientists, is "proof of concept for cell mediated repair of a neuronal circuit controlling a complex phenotype."