Insulin is even more important to your health than we thought - not only can problems with it cause diabetes, but they can also cause schizophrenia. The good news? This new discovery could lead to treatments for both conditions.
This link was identified in a study conducted by researchers at Vanderbilt University Medical Center, who discovered a definite link between malfunctioning insulin regulation in the brains of mice and increased incidence of schizophrenia-like behavior. It's not just that the same risk factors for diabetes can also lead to schizophrenia; it's that one condition can actually exacerbate the severity of the other from a behavior perspective.
Endocrinologist Kevin Niswender explains that recognition of this link could aid in the development of treatments that better address the multifaceted nature of patients' conditions:
"We know that people with diabetes have an increased incidence of mood and other psychiatric disorders. And we think that those co-morbidities might explain why some patients have trouble taking care of their diabetes."
The group, led by neurobiologist Aurelio Galli, had already that insulin doesn't just regulate glucose metabolism, but it also plays a major role in regulating the supply of the neurotransmitter dopamine to the brain. Problems in dopamine regulation can lead to depression, ADHD, Parkinson's, and schizophrenia. Now they've developed special mice that have helped them determine the precise molecular link between faulty insulin regulation, improper dopamine function, and schizophrenia-like behavior.
They impaired insulin function in mice, but only in their neurons. This allowed them to restrict their analysis purely to the brains of the mice. This impairment led to external behaviors that resembled those of schizophrenia patients, while internally the mice were found to have too little dopamine and too much norepinephrine in the prefrontal cortex, which is a crucial area for cognitive functions. Both of these were the result of an overabundance of the transmitter protein known as NET, which is supposed to help remove these neurotransmitters from the neural synapses.
Galli explains what he thinks is going on:
"We believe the excess NET is sucking away all of the dopamine and converting it to norepinephrine, creating this situation of hypodopaminergia (low levels of dopamine) in the cortex."
Giving the mice drugs that inhibit NET helped bring dopamine levels in the cortex back to normal, helping to also restore the mice to their original behaviors. This success has led to clinical trials in which schizophrenia patients will also be given NET inhibitors in the hopes that it will reduce the severity of their symptoms. This link also points to a very real link between the foods we eat and the moods we feel, and better understanding of the connection between insulin signaling and dopamine regulation could help develop better therapeutic treatments for those with schizophrenia.