Alzheimer's disease currently affects more than 5.5 million Americans and is one of the costliest diseases to treat, according to the Alzheimer's Association. Characterized by a buildup of plaque in the brain, few animal models exist that researchers could use to study this devastating disorder. Now a team of researchers has developed a rat model that can be used to study the buildup of amyloid plaques and vascular abnormalities in the brain.