Sensitivity to stress may make an individual vulnerable to development of self-injurious behaviors

An insight into development of self-injurious behaviors may be found in research on the neurobiology of response to stress among rats, according to a presentation at the 32nd annual meeting of the Society of Neuroscience. Findings from the animal research strongly suggest that individuals that are more easily stressed than their peers are also more vulnerable to development of self-injurious behaviors.

"This finding may help explain why some autistic and intellectually handicapped children deliberately hurt themselves while others do not," said Darragh P. Devine, Ph.D., presenter.

In the current research, investigators focused on the behavior that leads to injury. Other studies have almost exclusively consisted of examinations of traumatized tissue, without detailed behavioral analysis, according to Devine. Ultimately, the team wants to characterize individual differences in the development of self-injury in order to better define the progression of the devastating disorder. "It may tell us why some humans injure themselves and some do not," Devine noted.

An additional distinction between the current research and previous work is that the current experiments did not inevitably lead all of the subject animals to the point of self injury, which reflects the fact that some but not all high-risk children (for example, those with autism) exhibit head-banging or other similar behaviors.

The researchers regulated the dose of pemoline, a drug that resembles Ritalin and amphetamine, so that about 50 percent of the subject animals would self-injure, while 50 percent would not. Each experiment lasted six days. When the self-injurious behavior occurred, the experiment was ended so that the animals could not seriously harm themselves.

"We find that rats that are more highly responsive to a mild stressor, such as a new environment, secrete greater amounts of stress-related hormones," Devine said. "Some of the rats run around a lot and secrete a lot of hormones. These rats will more readily exhibit self-injury than will rats that do not respond so highly to the mild stress."

The research team is now examining how these individual differences arise. They measure the behaviors of rats living in an enriched environment compared with rats living in a stark one. Soon, they plan to analyze rat brain tissue on a molecular level.

"We'll look at the expression of the genes, differences in the neurotransmitters, things that make one rat different from the next," Devine said. "We're looking at some manipulations that may make rats more vulnerable or less vulnerable to self-injurious behavior. The rat
brains will show us what to look for in the human brain."






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