A stress-activated molecule underlies many of the symptoms of some mental illnesses, a new study shows.

We control our behaviors, thoughts, and emotions via an important part of the brain: the prefrontal cortex (search). People with injuries to this part of the brain become impulsive, distractible, and have poor judgment. Major damage to the prefrontal cortex can cause thought disorders and hallucinations.

These symptoms are also seen in people with bipolar disorder (search) and with schizophrenia (search). These mental illnesses worsen with stress.

Recent studies also link worsening bipolar disorder and schizophrenia with changes in brain signaling by a molecule called protein kinase C (search) or PKC.

In rat and monkey studies, Yale researcher Amy Arnsten, PhD, and colleagues delivered PKC directly to the prefrontal cortex of rats and monkeys. Sure enough, PKC impaired the animals' mental functioning.

Drugs that block PKC restored mental functioning. Some of these drugs include medicines commonly used to treat mental illness, such as lithium and valproate.

Arnsten and colleagues report their findings in the Oct. 29 issue of Science.

"Excessive PKC activation can disrupt ... regulation of behavior and thought, possibly contributing to signs of prefrontal cortical dysfunction such as distractibility, impaired judgment, impulsivity, and thought disorder," Arnsten and colleagues write.

It's possible that new drugs with improved PKC-blocking activity could lead to better treatment of bipolar disorder, schizophrenia, and perhaps other mental illnesses.

Interestingly, PKC plays a role in lead poisoning. The findings, Arnsten says, could lead to a better understanding of the symptoms of distractibility and impulsivity seen in children with lead poisoning.

By  Daniel J. DeNoon, reviewed by  Brunilda Nazario, MD

SOURCES: Birnbaum, S.G. Science, Oct. 29, 2004; vol 306: pp 882-884. News release, Yale University.