Insulin production has been discovered in the brain and linked to Alzheimer's disease, potentially changing how the illness is viewed and treated.
While insulin resistance, a characteristic of diabetes, is linked with neurodegeneration, the new finding provides a strong connection between diabetes and Alzheimer's disease.
"What we found is that insulin is not just produced in the pancreas, but also in the brain," says study senior author Suzanne de la Monte of Rhode Island Hospital and Brown University Medical School. "And we discovered that insulin and its growth factors, which are necessary for the survival of brain cells, contribute to the progression of Alzheimer's." 
This raises the possibility, says de la Monte, of a "type 3" diabetes. 
The finding was made by studying a genetic abnormality in rats that blocks insulin signaling in the brain.
In the rats, de la Monte and colleagues found that insulin and related proteins IGF I and II are expressed in neurons in several regions in the brain. 
Additionally, they determined that a drop in insulin production in the brain contributes to brain cell degeneration, a 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 researchers report. 
Analysis of postmortem brain tissue also revealed that the proteins aren't produced at normal levels in human Alzheimer's sufferers. 
Insulin and IGF I were significantly reduced in the frontal cortex, hippocampus and hypothalamus—all areas affected by Alzheimer's—while not in the cerebellum, which is generally not affected by Alzheimer's. 
The study "opens the way for targeted treatment to the brain and changes the way we view Alzheimer's disease," says de la Monte. 
The research is reported in the Journal of Alzheimer's Disease.

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Insulin levels tied to Alzheimer's