Identifying the Source of New Neurons in the Adult Hippocampus

Following on from recent confirmation of adult neurogenesis in humans, researchers here report on the identification of the stem cell population responsible for supplying neurons to the hippocampus in mice. The process by which new neurons are created and integrated into neural networks is considered an important target for future regenerative therapies. If the pace can be increased in older individuals, it may go some way towards reversing aspects of age-related cognitive decline, or enhance recovery after brain injury. Characterizing the stem cells responsible for creation of new neurons is an important step on the road towards targeted, selective upregulation of neurogenesis.

It was once believed that mammals were born with the entire supply of neurons they would have for a lifetime. However, over the past few decades, neuroscientists have found that at least two brain regions - the centers of the sense of smell and the hippocampus, the seat of learning and memory - grow new neurons throughout life. Researchers have now shown, in mice, that one type of stem cell that makes adult neurons is the source of this lifetime stock of new cells in the hippocampus. These findings may help neuroscientists figure out how to maintain youthful conditions for learning and memory, and repair and regenerate parts of the brain after injury and aging.

The researchers showed that the neural stem cells they found had a common molecular signature across the lifespan of the mice. They did this by labeling neural stem cells in embryos when the brain was still developing and following the cells from birth into adulthood. This approach revealed that new neural stem cells with their precursor's label were continuously making neurons throughout an animal's lifetime. This capacity is called plasticity, which is the brain's ability to form new connections throughout life to compensate for injury and disease and to adjust in response to new input from the environment. The next step for the researchers is to look for the same neural stem cells in other mammals, most importantly in humans, starting the search in post-mortem brain tissue, and to investigate how this population of neural stem cells are regulated.



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