"The persistence of these symptoms over several decades was
evidence that they were long-lasting changes," Dr. Krystal says.
By the 1980s, evidence from studies with laboratory animals was
pointing to a specific site of those brain changes: the noradrenaline
system, which rouses the body for emergencies. Trauma seems to reset the
brain's noradrenaline system, making people prone to adrenaline surges
even decades later. Such surges can be triggered by anything resembling
the original trauma--or they can come out of the blue.
One site of changes in the brain has been pinpointed: Yohimbine
blocks the action of the alpha-2 receptor located on the noradrenaline
neuron. This allows more noradrenaline to be released for a longer time
in the brain, which mobilizes the body for an emergency that exists only
in the mind.
Other studies at the West Haven research center show that a trauma
could sensitize people to adrenaline. In one, John Mason, M.D., found
that PTSD sufferers had abnormally high levels of adrenaline and
noradrenaline in their bodies. In another, led by Bruce Perry, M.D. (now
at the University of Chicago), PTSD patients were found to have 40
percent fewer alpha-2 receptors on their blood platelets.
These changes may also occur in the locus coeruleus, which
coordinates the secretion of the hormones adrenaline and noradrenaline,
which course through the body to prepare it for an emergency. About 90
percent of the cells for the brain's noradrenaline-controlling system are
in the locus coeruleus or connect directly to it. One major trunk of
these connections runs to the limbic system, the system that modulates
emotions; another runs to the frontal cortex, which involves planning and
rational decision-making.
In other words, researchers found a series of neurobiological
changes that left PTSD sufferers with an altered brain
metabolism--vulnerable to surges of noradrenaline--thus prompting the
alarm states.
Millions of Americans endure intense trauma each year, and many of
them may be suffering the symptoms of PTSD. A 1989 study of 1,007 men and
women ages 21 to 30 who are members of a large health plan in Detroit
found 39 percent had at sometime in their lives endured the type of
trauma that can lead to PTSD. Of those, one in four developed symptoms of
posttraumatic stress, according to Naomi Breslau, Ph.D., a sociologist
specializing in psychiatric epidemiology at the Henry Ford Hospital in
Detroit.
If Dr. Breslau's findings are confirmed by other studies, as many
as one in 10 young Americans is likely to suffer from the symptoms of
PTSD at some point in his or her life. Yet only a small number of PTSD
victims recognize the source of their trouble, let alone seek help for
their symptoms.
Scientists have yet to determine what type of person is most
susceptible to PTSD, but one clue may come from dozens of studies with
animals that show that suffering severe, trauma in early life increases
susceptibility to the impact of other trauma later on. One implication is
that people who were victims of abuse as children may be among the most
vulnerable to PTSD as adults. "Once you're exposed to early kinds of
stresses, you're more reactive to later ones," says the VA's Dr.
Krystal.
As researchers have focused on trauma and the brain, they have
found two other major shifts in addition to the noradrenaline system's
increased vulnerability to adrenaline rushes: One of the main changes is
in the brain circuit linking the hypothalamus and the pituitary gland.
During stress, this circuit triggers the release of CRF, an important
stress hormone. Trauma seems to leave this brain system prone to
oversecreting CRF, thereby reacting to emergencies that do not exist in
reality.
In a study similar to the yohimbine experiment, PTSD patients at
Duke University Medical School were injected with CRF, which typically
causes people to secrete large amounts of ACTH, a chemical that then
triggers the stress reaction. But the PTSD victims had an unusual
response: They secreted far less ACTH. That apparent paradox is actually
a sign that the PTSD victims had been secreting ACTH far more than usual
before their injection.
"That implies that these patients have been chronically
hypersecreting CRF," says Charles Nemeroff, M.D., the psychiatrist at
Duke University who did the study. "The reason is that if you continually
oversecrete CRF, the brain compensates by decreasing the number of
receptors for CRF."
But the decrease in receptors is not steep enough to mutes the
effects of too much CRF. The CRF oversecretion may explain many of the
symptoms of PTSD, compounding the effects of adrenaline surges. "Too much
CRF makes you exaggerate the danger of things, so you overreact," says
Dr. Nemeroff. "If you have PTSD from battle in the Gulf War and you hear
a car backfire in the shoppingmall parking lot, too much CRF floods you
with the same feelings you had in combat: You're scared; you start
sweating or begin to get the chills."
The third brain area that shows a change in PTSD is the opioid
system, which serves to blunt the sensations of pain during an injury.
The best-known class of opioids are the endorphins--brain chemicals that,
like the other opioids, act at the same site in the brain as opium and,
like that drug, dull pain while evoking a pleasant, detached
dreaminess.
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