Stem cells could potentially be used to repair the damage to brain tissue caused by a stroke, say scientists.
Stem cells hold great potential
A team from Stanford University injected foetal stem cells into stroke-damaged rats' brains.
They found the cells could migrate to the damaged areas, and turn into the right type of brain cell. Whether they actually aid recovery is still unknown.
The research is published in the journal Proceedings of the National Academy of Sciences.
A stroke leaves a permanent gap in the brain that can destroy a person's ability to speak and move normally.
Scientists believe it should be possible to use stem cells - the body's master cells with the potential to turn into any type of tissue - to fill the gap.
This is what the Stanford team has done in experiments on rats. If these cells also replace the function of the lost cells, they could help people recover after a stroke.
Lead researcher Dr Gary Steinberg said: "We are not saying we can treat patients immediately, but it is a big step forward.
"This gives us considerable optimism for these cells."
When stem cells were injected close to the site of the induced stroke, the cells survived in only one out of nine rats.
This is because the stroke site does not have a blood supply to keep the cells alive.
However, when injected a few millimetres away, the cells survived and migrated as far as 1.2 millimetres toward the stroke region.
Dr Steinberg believes signals from the damaged cells act as a distress call beckoning the transplanted cells.
Other signals direct the newly arrived cells to transform into neurons (brain cells) and support cells called astrocytes.
In rats without an induced stroke, the injected cells migrated only an average of 0.2 millimetres.
The next stage will be to assess whether the stem cells can actually help aid recovery from a stroke.
Dr Michael Marks, of the Stanford Stroke Center, said there was currently no way to treat patients who had lost brain function after a stroke.
He said: "A therapy like this has tremendous potential."
Stem cells can be taken from adult tissue, as well as foetal tissue.
But the Stanford team found that when these cells were injected into areas of stroke damage did not survive long, or migrate to the correct location.
A spokesperson for the Stroke Association said the organisation was currently working on a project investigating the use of adult bone marrow stem cells to repair damaged brain tissue caused by stroke.
"We fully support any further developments in this specific field of stem cell research which may help stroke patients receive better treatment in the future."