Scientists have repaired a natural gateway into the brains of mice, allowing the clumps and tangles associated with Alzheimer's disease to be swept away. After just three drug injections, mice with certain genes that mimic Alzheimer's showed a reversal of several key pathological features. Within hours of the first injection, the animal brains showed a nearly 45 percent reduction in clumps of amyloid-beta plaques, a hallmark of Alzheimer's disease. The mice had previously shown signs of