Via EurekAlert!: "For years, researchers seeking new therapies for traumatic brain injury have been tantalized by the results of animal experiments with stem cells. In numerous studies, stem cell implantation has substantially improved brain function in experimental animals with brain trauma. But just how these improvements occur has remained a mystery. Now, an important part of this puzzle has been pieced together by researchers ... In experiments with both laboratory rats and an apparatus that enabled them to simulate the impact of trauma on human neurons, they identified key molecular mechanisms by which implanted human neural stem cells - stem cells that are in the process of developing into neurons but have not yet taken their final form - aid recovery from traumatic axonal injury. A significant component of traumatic brain injury, traumatic axonal injury involves damage to axons and dendrites, the filaments that extend out from the bodies of the neurons. The damage continues after the initial trauma, since the axons and dendrites respond to injury by withdrawing back to the bodies of the neurons. ... Axons and dendrites are the basis of neuron-to-neuron communication, and when they are lost, neuron function is lost. In this study, we found that our stem cell transplantation both prevents further axonal injury and promotes axonal regrowth, through a number of previously unknown molecular mechanisms. ... We identified about 400 proteins that respond differently after injury and after grafting with neural stem cells. ... a group of cytoskeleton proteins was being changed, and in particular one called alpha-smooth muscle actin, which had never been reported in the neurons before.""