(cont)
"We see big differences in people who have experienced acute stress compared to chronic stress," he says. "The [body's] machinery becomes very different." If the stress remains long enough, a person may develop major depression.

It is this kind of finding, say the UM researchers, that provides one reason to believe that depression has important connections to the stress axis, and why much research at the MHRI on this topic has involved clinical studies of people with major depression.

Overall, says Akil, the stress axis uses "nested loops" of neurons and chemical messengers to provide many avenues for regulating the body's response to stress. Controls via the genetic machinery appear to "define the limits" of the stress response. Other pathways probably provide the various nuances of response. Many control mechanisms, however, remain to be discovered.