PORTLAND, Ore. (AP) -- Stress from abuse or neglect early in life may be linked to increased mental health problems during adolescence, according to a new study based on animal research.

Children who have suffered abuse, neglect, or loss of a parent have an increased risk behavioral and emotional problems, including attention deficit and hyperactivity disorder, anxiety, depression, suicide and drug abuse, according to Oregon Health & Science University researchers.

The study was based on rhesus macaque monkeys that were exposed to a stressful event before they were raised in a stable family environment.

"By studying a species that has responses to early-life stresses that are very similar to young children, we can get a developmental picture that is much clearer than in humans," said Judy Cameron, a senior scientist at the OHSU Oregon National Primate Research Center.

Interpretations of human studies are often difficult because children experiencing early-life stresses frequently are exposed to many other situations that can influence behavior, Cameron said.

The monkey study provides strong evidence that stress exposure early in life can have dramatic, long-lasting effects that persist into the teenage years and perhaps even adulthood, she said.

The researchers studied 16 small social groups of monkeys for a three-year period. Because monkeys mature at a much more accelerated pace than humans, a monkey 2 to 4 years old would correspond to a human teenager.

Certain monkeys were removed from their mothers at various stages early in life. These monkeys continued to be raised in the stable social groups with other monkeys -- similar to a human child who suffers the stress of losing a parent but continues to be raised in their family.

The behavior of the monkeys appeared similar to children who develop a form of attachment disorder characterized by withdrawal from social interactions.

Dr. Ronald Dahl, a University of Pittsburgh psychiatrist, said the study provided "unique insights into these developmental interactions in ways that can not be achieved in controlled studies in humans."

The research should help answer some important clinical questions about targeting early intervention for behavioral and emotional problems in youth, he said.

The study was presented this week during the Society for Neuroscience meeting in Washington, D.C.

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