(The Associated Press) - New research suggests that serotonin, an all-purpose neurotransmitter already known to play a vital role in many behaviors and emotions, appears to be implicated in regulating anxiety as well.

In experiments with bioengineered mice, researchers showed that animals lacking serotonin early in life when their brains were rapidly developing displayed anxious behaviors as adults.

This suggests there is an early window during which serotonin is necessary to establish the proper brain circuitry that is essential for normal emotional behavior throughout life, they said.

Researchers said these findings in mice may be relevant to anxiety disorders in people. Serotonin levels already have been linked to depression, migraine headaches and irritable bowel syndrome.

The findings eventually could lead to a new way of treating anxiety-related illnesses that focus on serotonin circuitry, said the study's author, Rene Hen of Columbia University. His report appears in the current issue of the journal Nature.

"Traditionally, when you treat adults for anxiety or depression with drugs, you assume you're treating the causes of the disorder," Hen said. "The postnatal period appears to be a period of high vulnerability. It's a time when proper wiring of your brain is really critical to the behaviors that are going to be displayed later on in life."

In the experiments, Hen and colleagues effectively blocked serotonin receptors in different locations of the brains of bioengineered mice by a variety of methods. They repeated the experiments throughout key phases of the animals' lives.

If the mice appeared anxious - eating less or balking at moving through elevated mazes - the researchers surmised the serotonin receptor location was important in controlling anxiety.

Later, they repeated many of the experiments with mice that were bioengineered so the serotonin receptors were only active in their forebrains, which control complex behaviors.

Mice without the receptors between five and 21 days after birth became very anxious as adults, the researchers found.

Mice that were deprived of serotonin only as adults did not show similar effects, they reported.

Scientists who did not participate in the study said its systematic approach could be useful in determining the chemical pathways of other disorders.

The results also suggest that some anti-anxiety medications that do not take serotonin into account might be treating symptoms, but not the causes of anxiety disorders.

"If they can do this for one form of serotonin receptors, you can do it for receptors for lots of other neurotransmitters." said Solomon H. Snyder of Johns Hopkins University School of Medicine.

Snyder said the treatment of other emotional disorders, such as depression and schizophrenia, may also benefit from similar research, as well as prenatal care.

"What if a pregnant mother is taking a drug that affects serotonin systems?" Snyder said. "That could conceivably affect systems in the brain of her baby that are relevant to anxiety."

Additionally, new research is examining whether early serotonin deficiencies can create abnormal circuitry that allows for post-traumatic stress disorder and separation anxiety.

Said Dr. Joseph Coyle of Harvard Medical School: "It really shines the light on the importance of development in the ultimate manifestation of these behaviors that are linked to anxiety."

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