Washington: Adult stem cells actually originate in a different part of the brain unlike previously believed and can be coaxed into producing new brain cells to replace those lost to disease or injury.

True stem cells, as evidence shows, are ependymal cells lining brain and spinal cord ventricles, rather than cells in the sub-ventricular zone, as previously believed.

Stem or "master cells" produce each of the specialised cells in the body. If researchers could control the production and differentiation of stem cells, they may be able to use them to replace damaged tissues.

"The cells already match your brain completely since they have the same genetic make-up. That is a huge advantage over any other approach that uses cells from a donor," said Darius Gleason, the study's co-author.

"If they are your cells, then all we are doing is helping your body fix itself. We're not reinventing the repair process," added Gleason, also a graduate student in the department of developmental and cell biology, University of California.

Researchers are focusing on transplantation, which entails injecting healthy cells that may or may not match the patient. In the latter eventuality, drugs are used to prevent the body from rejecting the treatment.

But working with a patient's own cells would eliminate the need for transplantation and immunosuppressant drugs and may be a better alternative, scientists said.

In this study, Gleason and Peter Bryant, developmental and cell biology professor, used rats treated to develop the animal equivalent of Parkinson's disease.

They chose this type of rat because in a previous study by University of California collaborator James Fallon, a small protein given to the brain-damaged rats sparked a rapid, huge production and migration of new cells, and significantly improved motor behaviour.

First, the researchers sought to determine the true location of stem cells in the rats by looking for polarized cells, which have different sets of proteins on opposite sides so that when one divides it can produce two different products.

Polarization gives rise to asymmetric cell division, which produces one copy of the parent and a second cell that is programmed to turn into another cell type. Asymmetric cell division is the defining characteristic of a stem cell.

"It couldn't have been a stronger signal or clearer message. We could see that the only cells undergoing asymmetric cell division were the ependymal cells," Gleason said. IANS