Number of nerve stem cells declines with age
A new study may explain why our brains produce fewer new neurons with age. Mice were genetically modified so that their brain cells were tagged with fluorescent colours. This allowed different types of brain cell to be visually identified and counted.
Blood stem cells, for example, go through many cycles of self-renewal and their numbers do not decline with age. In contrast, the adult stem cells in the brain remain quiescent until they are activated. They then undergo a series of rapid divisions that give rise to neurons. After that, the stem cells differentiate into astrocytes, a type of non-neural 'helper' cell, so the total number of brain stem cells decreases with age.
Between one month and two years of age there was a 100-fold decrease in the number of brain stem cells in the GM mice.
Brain stem cells can be activated by brain injury and Parkinson's Disease, depleting the stem cell pool. In contrast, exercise and deep brain stimulation stimulate the production of new neurons from stem cell daughter cells and do not reduce the store of brain stem cells.
Read about deep brain stimulation for Parkinson's Disease and view the video demo here.