Researchers from Lund University and KarolinskaInstitutet in Sweden have uncovered a previously unknown mechanism by which the brain generates new nerve cells after a stroke. Their findings are published in the Oct. 10 issue of the journal Science. Strokes are caused by blood clots that block the brain’s blood clots, leading to disruptions in blood flow and causing a lack of oxygen. A large number of nerve cells die thereby causing a range of motor, sensory and cognitive problems. By tracking mice with induced strokes, researchers have shown that supporting cells called astrocytes initiate the formation of nerve cells at the site of brain damage (extended reading: New Nature article: The astrocyte that can’t be ignored). Using a number of genetic methods to map the fate of these cells, the scientists confirmed that astrocytes in this region form immature neuronal cells, which subsequently develop into mature neuronal cells. ZaalKokaia, professor of experimental medicine research at Lund University, said, “This is the first confirmation that astrocytes can initiate a process that prompts the generation of new nerve cells after a stroke.” The scientists also identified the signaling mechanism that regulates the conversion of astrocytes into neuronal cells. In healthy brains, activation of this signaling mechanism inhibits this transformation, so astrocytes do not generate neural cells. After a stroke, this signaling mechanism is inhibited and astrocytes can initiate the process of generating new cells. ZaalKokaia said, “Interestingly, even when we blocked this signaling mechanism in mice not subjected to stroke, astrocytes formed new nerve cells.” ”This suggests that not only stroke can activate this potential process in astrocytes. Therefore, this mechanism could potentially be a useful target for generating new nerve cells that replace dead cells after other brain diseases or injuries.” The researchers found that these new nerve cells form specific contacts with other cells. And whether these nerve cells are functional, and their contribution to the spontaneous recovery after stroke seen in most experimental animals and patients, remains to be confirmed. A decade ago, Kokaia and Lindvall’s group first demonstrated that stroke leads to the formation of new nerve cells from the adult brain’s own neural stem cells. The new findings further underscore that when the adult brain suffers a major blow such as a stroke, it strives to use a variety of mechanisms to repair itself. An important breakthrough in this study is the first evidence that the adult brain’s self-repair is linked to astrocytes entering a process that changes their identity to become neural cells. ”A major task now is to explore whether astrocytes in the human brain also transform into neurons after injury or disease. Interestingly, it is known that in the healthy human brain new neuronal cells are formed in the striatum. The new data raise the possibility that some of these neuronal cells are generated by localized astrocytes. If this new mechanism also works in the human brain and can be enhanced, it would not only be clinically important for stroke patients, but could also replace dead neurons and thus restore function in patients with other diseases such as Parkinson’s and Huntington’s,” said Olle Lindvall, senior professor of neurology.