Older and wiser

 作者:蒯凰     |      日期:2019-03-07 05:19:12
By Philip Cohen San Francisco THE shrinkage of cells in the brains of old monkeys can be reversed, neuroscientists say. If the same is possible for people, it may help prevent mental decline in old age. The cause of the measurable loss of memory and concentration that come with normal ageing is still shrouded in mystery. While Alzheimer’s disease and some other age-linked disorders kill off neurons, neuroscientists have found little evidence for the death of neurons in healthy people or other primates when they get old. More subtle changes are thought to be responsible for mental decline. To find out more, Mark Tuszynski of the University of California at San Diego and his colleagues looked for changes in a thin strip of cells called Ch4 cells in a region of the brain directly between the ears. “These cells are like air traffic controllers, coordinating the higher functions of the brain,” says Tuszynski. Death of these cells causes some of the symptoms of Alzheimer’s. When the team looked at these cells in the brains of four young and three old monkeys, they found no evidence that the cells had died in the older animals. However, the old monkeys showed a 43 per cent reduction in the number of cells containing detectable amounts of a protein called p75, which they need in order to work properly. Those that did produce p75 were 10 per cent smaller in the old monkeys, suggesting they were shrinking and might eventually die. But Tuszynski could reverse this. In four other old monkeys, his team implanted cells that secreted nerve growth factor near the Ch4 cells. NGF is known to stimulate this class of neurons. When the researchers examined the Ch4 cells three months later, their p75 production and size were near that of a young animal (Proceedings of the National Academy of Sciences, vol 96, p 10 893). “I like this experiment,” says John Morrison, a neuroscientist at Mount Sinai Medical Center in New York. “That this atrophy can be reversed should make people optimistic.” But he points out that it’s not yet clear whether the treatment slows or reverses cognitive deficiencies in monkeys. Tuszynski plans to test this. He thinks it may also be possible to use brain imaging to see how diet or drugs affect Ch4 cells, in the hope that this might lead to less drastic treatments to prevent mental decline. He suspects other neurons are probably also involved. “I’d be very surprised if this was the only neuronal system affected by ageing,