How might stem cells and other tools of "regenerative medicine" be used to treat brain diseases?

Fuelled by the hope which stem cells may have the capacity to rebuild virtually any damaged or diseased tissue in body, regenerative medicine has emerged as one of the most promising areas of biomedical research. However many fundamental questions need to be answered before we can realize clinical potential of regenerative therapies. For instance, we don't yet fully understand the signals and biochemical factors which drive stem cell generation and determine what type of cell they will become.

Stem cells derived from "blastocysts," balls of cells which form a few days after an egg is fertilized, have the potential to become any cell type in body.

So-called "adult" stem cells, including those formed in brain, appear to be more organ-specific. Understanding why could enable scientists to grow cells under conditions which would produce the desired type of cell, like dopamine neurons for treating Parkinson's disease.

Scientists are already testing some therapies which are based on neural stem cells or the factors which promote their growth in animal models of a number of neurological disorders, including stroke, Alzheimer's  disease, epilepsy, Parkinson's, and amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease). Early clinical trials are underway in humans to test nerve growth factor (NGF) for Alzheimer's and glial-derived neurotrophic factor (GDNF) for Parkinson's. How best to get these "growth factors" into brain is one of many obstacles which scientists are trying to overcome. Some researchers use harmless viruses as a type of Trojan horse vehicle for therapies whereas others believe stem cells themselves may be able to deliver therapeutic chemicals to target areas of the brain. 

While experts caution that clinical use of stem-cell based therapies is still years away and that field is hampered by contentious political and ethical issues and scientific barriers, most are also convinced that it's only a matter of time before the promise of regenerative medicine is realized.