Apr. 10, 1998 WASHINGTON, D.C. April 8 -- New research indicates that exposure to stress during puberty results in abnormal aggressive and submissive behaviors as well as neurobiological alterations in hamsters.
"The findings underscore the effects of social stress during puberty in hamsters," says the study's lead author, Yvon Delville, PhD, an assistant professor in the psychiatry department at the University of Massachusetts Medical Center in Worcester. "The results also show that an imbalance in the vasopressin and serotonin brain chemical systems may contribute to inappropriate behavior."
Delville's study, funded by the National Institute of Mental Health and a Joseph P. Healy Endowment award, is published in the April 1 issue of The Journal of Neuroscience.
"These robust data show the importance of experience during the adolescent period on the maturation of neural systems and behavior," says stress expert, Michael Meaney, PhD, of Douglas Hospital Research Centre in Montreal. "Puberty has been a greatly underestimated area of study."
The researchers' first finding demonstrates that exposing adolescent male hamsters to stress by caging them with bullying adults alters their behavior. The stressed hamsters become more fearful of animals their own size than unstressed siblings. On the other hand, they become more likely to bite and attack small, more vulnerable animals.
A second finding indicates that the behavior changes are associated with alterations in two brain chemical systems. "We found that the animals that experienced the stress during puberty had reduced levels of the chemical vasopressin and an increased density of serotonin nerve cell terminals in the brain area known as the hypothalamus," says Delville. Previous research showed that vasopressin facilitates aggressive behavior and that serotonin inhibits aggressive behavior in hamsters and other species.
"We suspect that the stressed hamster has a decreased release of vasopressin and an enhanced release of serotonin when it confronts a hamster that resembles itself," says Delville. "And the reverse may occur when the stressed hamster encounters a meeker hamster."
The researchers plan to test their theory further by examining vasopressin and serotonin activity in hypothalamus samples taken from the stressed hamsters while they were interacting with other hamsters. They also hope to determine if other chemicals are involved in the behavior changes and whether the chemical alterations are reversible.
Delville is a member of the Society for Neuroscience, an organization of more than 27,000 basic scientists and clinicians who study the brain and nervous system. The Society publishes The Journal of Neuroscience.
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