Monday, 11 November, 2002, 18:12 GMT
Scientists have found a way of making human embryonic stem cells implanted into the brains and spinal cords of rats develop into nerve cells.
It could bring treatments for neurodegenerative diseases like Parkinson's
and Alzheimer's a step closer to reality.
Previous attempts to replace damaged nerve cells have failed, with only a few cells developing into neurons.
By treating the stem cells with chemicals, the scientists succeeded in changing them into neurons.
But despite this advance the researchers say there is still a long way to go before stem cells will lead to new treatments for humans.
Stem cell research is being hailed by many scientists as the tool that could give rise to cures for diseases where cells are damaged in the brain and the spinal cord.
But a major obstacle to this has been that only a few stem cells become neurons when placed in most brain areas.
Now though, new research published in the journal Nature Neuroscience may have overcome this.
Scientists from the University of Texas, US, have pre-treated human embryonic stem cells with a mixture of chemicals needed for nerve cell development.
The following day they injected these cells into the central nervous system of healthy rats and the primed cells then developed into exactly the right type of neurons for the area that they were implanted into.
Professor Ping Wu from the University of Texas said: "This priming seems to get the cells into a plastic intermediate stage, and then after they're injected they acquire environmental cues and become specific kinds of neurons according to where they're located."
The researchers are continuing their work and are now injecting the primed cells into rats with spinal cord injuries.
"The next challenge will be to see if the neurons can actually make the right contact to the right targets - for example, if motor neurons are transplanted into the spinal cord, whether they can send fibres, or axons, to muscle," Professor Wu said.
But there are still many stages to overcome before treatments for human conditions can begin to be developed.
"Then we'll see if they can release the neurotransmitters, and then look at function to see if there is a long-term functional recovery.
"We also need to confirm that there is no tumour formation from the
implanted stem cells. Then we're talking about real clinical significance
and real clinical trials."
© Copyright 2002, BBC