By studying a gene abnormality in rats that blocks insulin signaling in the brain, researchers found that insulin and IGF I and II are all expressed in neurons in several regions in the brain.

Additionally, researchers determined that a drop in insulin production in the brain contributes to the degeneration of brain cells, an early symptom of Alzheimer's. "These abnormalities do not correspond to Type 1 or Type 2 diabetes, but reflect a different and more complex disease process that originates in the CNS (central nervous system)," the paper states.

By looking at postmortem brain tissue from people diagnosed with Alzheimer's disease, researchers discovered that growth factors are not produced at normal levels in the hippocampus - the part of the brain responsible for memory. The absence of these growth factors, in turn, causes cells in other parts of the brain to die. Reserachers found that insulin and IGF I were significantly reduced in the frontal cortex, hippocampus and hypothalamus - all areas that are affected by the progression of Alzheimer's. Conversely, in the cerebellum, which is generally not affected by Alzheimer's, scientists did not see the same drop in insulin and IGF I.

"Now that scientists have pinpointed insulin and its growth factors as contributors to Alzheimer's, this opens the way for targeted treatment to the brain and changes the way we view Alzheimer's disease," de la Monte says.

The study was supported by grants from the National Institute of Alcoholism and Alcohol Abuse and from a COBRE award from the National Institutes of Health.