New research into anxiety disorders – Part II
Previously, researchers assumed that the stress “parking brake” system acted the same in everyone. But new research during the November conference points to a different model — that some people’s brains synthesize more endocannabinoids than others, and that people with higher levels can handle more stress.
Researchers have long known that some people can take more metaphorical heat than others. “Some kids can undergo a lot of traumatic events in early life and turn out just fine,” said University of Michigan researcher Pam Maras. “Some undergo relatively minor things and turn out to have severe anxiety and depression.” Numerous researcher teams are using rat models to try to understand how stress responses can be manipulated, and they reported their findings at the conference.
In separate experiments, Gray and Lim tinkered with endocannabinoid levels in rats. Both found that rats with higher levels acted less anxious after being exposed to stress. Lim made part of a maze scary by tainting it with the scent of a fox’s feces. Rats with more stress-braking power would explore the tainted regions of the maze. More timid rats avoided it for as long as seven days after the scent was laid down.
Two other research groups, working independently in Ohio and Colorado, manipulated CRH levels in different ways but arrived at complementary results. At Kent State University, neuroscientist Lee Gilman blocked CRH receptors in mice, shutting out the stressinducing peptide and enabling them to approach other, unfamiliar mice.
At the University of Colorado-Boulder, Christopher Lowery is interested in how the brain responds to repeated social defeat. For example, what happens when a child is repeatedly bullied? He mimicked this by putting a male rat into the home cage of another male rat, where the newcomer would be forced to surrender to the more dominant native. In his study, rats that faced social defeat over and over produced more CRH each time, and were more quickly immobilized by fear during later encounters.
However, as Lim and Gilman both observed, some animals can put the brake on anxiety longer than others. Clinicians know this is true for humans; what the laboratory scientists are probing is when and how those differences manifest in the brain.
Michigan researcher Pam Maras sees evidence that these differences begin early in development. Her more nervous rats began displaying excessive anxiety as early as 11 days after birth, which corresponds to the fifth week of life for an infant. Animals that did not manifest anxiety at that point grew up to be more resilient to stress, though Maras can’t say why.
“We don’t have an answer for that right now,” said Maras. “It’s exciting sometimes when you don’t have an answer, because that means that there’s more to do.” Some people are probably born more vulnerable to anxiety disorders than others. And although they might benefit greatly from a medication that puts a brake on runaway anxiety, scientists have a lot to learn before such a drug will be ready for clinical use.
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