Brain cells that were grafted into the brains of mice have become fully functionally integrated after six months. The successful neuron transplant could pave the way for therapies to treat neurodegenerative diseases such as Parkinson's.

A team of stem cell researchers at the Luxembourg Centre for Systems Biomedicine created the grafted neurons -- induced neuronal stem cells -- in a petri dish out of the host's reprogrammed skin cells. This technique dramatically improved the compatibility of the implanted cells.

Six months after the brain cells were implanted into the hippocampus and cortex regions of the brain, the neurons were fully integrated with the original brain cells via newly formed synapses (the contact points between neurons). The induced neuronal stem cells had changed into different types of brain cells -- neurons, astrocytes and oligodendrocytes -- over time within the host brain. Functional integration with the existing network of cells is absolutely critical for long-term survival of the new brain tissue. The new brain cells exhibited normal activity in tests and the mice showed no adverse side effects.

The plan for researchers is now to explore replacing the type of neurons that tend to die off in the brain of Parkinson's patients -- those neurons found in the substantia nigra that produce dopamine. It may, in the future, be possible to implant neurons to produce the diminished dopamine, which could prove to be an effective treatment for the disease.

Of course, it's a bit leap from the current research to human trials. "Successes in human therapy are still a long way off, but I am sure successful cell replacement therapies will exist in future," says team leader and stem cell researcher Jens Schwamborn. "Our research results have taken us a step further in this direction."

The study has been published in Stem Cell Reports and is available to read for free.

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Implanted brain cells integrate fully with mouse brain tissue