Human embryonic stem cells (hESCs) were used to create precursor nerve cells, which were transplanted into mice. This triggered neuron growth and appeared to improve memory function, according to the team from the University of Winconsin-Madison, USA.
The researchers began by damaging an area of the brain known as the medial septum in the mice. This is connected to the hippocampus - which has a central role in memory and navigation - with brain cells known as cholinergic and GABA, gamma-Aminobutyric acid neurons.
The team then added chemicals to hESCs to encourage them to develop into precursor nerve cells. These were then transplanted into the hippocampus, where they formed cholinergic and GABA neurons.
'These two neuron types are involved in many kinds of human behaviour, emotions, learning, memory, addiction and many other psychiatric issues', says Dr Su-Chun Zhang, lead author on the study. 'Cholinergic neurons are involved in Alzheimer's and Down's syndrome, but GABA neurons are involved in many additional disorders, including schizophrenia, epilepsy, depression and addiction'.
After the transplant, the mice scored better in standard memory tests such as navigating their way out of a water maze. This suggested that the function of the medial septum had been restored, and that hippocampus function had been improved.
In some previous stem cell transplants, cells have grown uncontrollably and formed tumours (reported in BioNews 496). Dr Zhang believes that starting the process of specialisation in the embryonic stem cells was vital in preventing tumours from forming. 'In many other transplant experiments, injecting early progenitor cells resulted in masses of cells - tumours. This didn't happen in our case because the transplanted cells are pure and committed to a particular fate so that they do not generate anything else', he said.
While the study demonstrates that it is possible to treat damaged parts of the brain, it is unlikely that this type of stem cell therapy will be used to treat neurological disorders in humans in the near future. 'For many psychiatric disorders, you don't know which part of the brain has gone wrong', said Dr Zhang. He believes the research will help create models for drug screening and development.