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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