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Irritable Bowel Syndrome
The person with this syndrome experiences intermittent bouts of gastrointestinal cramps
and diarrhea or constipation, often occurring during a period of stress. Because the
symptoms are so pronounced, panic disorder is often not diagnosed when it occurs in a
person with irritable bowel syndrome.
Mitral Valve Prolapse
This condition involves a defect in the mitral valve, which separates the two chambers
on the left side of the heart. Each time the heart muscle contracts in people with this
condition, tissue in the mitral valve is pushed for an instant into the wrong chamber. The
person with the disorder may experience chest pain, rapid heartbeat, breathing
difficulties, and headache. People with mitral valve prolapse may be at higher than usual
risk of having panic disorder, but many experts are not convinced this apparent
association is real.
CAUSES OF PANIC DISORDER
The National Institute of Mental Health supports a sizable and multifaceted research
program on panic disorder—its causes, diagnosis, treatment, and prevention. This
research involves studies of panic disorder in human subjects and investigations of the
biological basis for anxiety and related phenomena in animals. It is part of a massive
effort to overcome the major mental disorders, an effort that is taking place during the
1990s—the Decade of the Brain. Here is a description of some of the most important
new research on panic disorder and its causes.
Genetics
Panic disorder runs in families. One study has shown that if one twin in a genetically
identical pair has panic disorder, it is likely that the other twin will also. Fraternal,
or non-identical twin pairs do not show this high degree of "concordance" with
respect to panic disorder. Thus, it appears that some genetic factor, in combination with
environment, may be responsible for vulnerability to this condition.
NIMH-supported scientists are studying families in which several individuals have panic
disorder. The aim of these studies is to identify the specific gene or genes involved in
the condition. Identification of these genes may lead to new approaches for diagnosing and
treating panic disorder. Families interested in participating in such a study should call
the NIMH at (301) 496-8977.
Brain and Biochemical Abnormalities
One line of evidence suggests that panic disorder may be associated with increased
activity in the hippocampus and locus ceruleus, portions of the brain that monitor
external and internal stimuli and control the brain's responses to them. Also, it has been
shown that panic disorder patients have increased activity in a portion of the nervous
system called the adrenergic system, which regulates such physiological functions as heart
rate and body temperature. However, it is not clear whether these increases reflect the
anxiety symptoms or whether they cause them.
Another group of studies suggests that people with panic disorder may have
abnormalities in their benzodiazepine receptors, brain components that react with
anxiety-reducing substances within the brain.
In conducting their research, scientists can use several different techniques to
provoke panic attacks in people who have panic disorder. The best known method is
intravenous administration of sodium lactate, the same chemical that normally builds up in
the muscles during heavy exercise. Other substances that can trigger panic attacks in
susceptible people include caffeine (generally 5 or more cups of coffee are required).
Hyperventilation and breathing air with a higher-than-usual level of carbon dioxide can
also trigger panic attacks in people with panic disorder.
Because these provocations generally do not trigger panic attacks in people who do not
have panic disorder, scientists have inferred that individuals who have panic disorder are
biologically different in some way from people who do not. However, it is also true that
when the people prone to panic attacks are told in advance about the sensations these
provocations will cause, they are much less likely to panic. This suggests that there is a
strong psychological component, as well as a biological one, to panic disorder.
NIMH-supported investigators are examining specific parts of the brain and central
nervous system to learn which ones play a role in panic disorder, and how they may
interact to give rise to this condition. Other studies funded by the Institute are under
way to determine what happens during "provoked" panic attacks, and to
investigate the role of breathing irregularities in anxiety and panic attacks.
Animal Studies
Studies of anxiety in animals are providing NIMH-sponsored researchers with clues to
the underlying causes of this phenomenon. One series of studies involves an inbred line of
pointer dogs that exhibit extreme, abnormal fearfulness when approached by humans or
startled by loud noises. In contrast with normal pointers, these nervous dogs have been
found to react more strongly to caffeine and to have brain tissue that is richer in
receptors for adenosine, a naturally occurring sedative that normally exerts a calming
effect within the brain. Further study of these animals is expected to reveal how a
genetic predisposition toward anxiety is expressed in the brain.
Other animal studies involve macaque monkeys. Some of these animals exhibit anxiety
when challenged with an infusion of lactate, much like people with panic disorder. Other
macaques do not exhibit this response. NIMH-supported scientists are attempting to
determine how the brains of the responsive and non- responsive monkeys differ. This
research should provide additional information on the causes of panic disorder.
In addition, research with rats is exploring the effect of various medications on the
parts of the brain involved in anxiety. The aim is to develop a clearer picture of which
components of the brain are responsible for anxiety, and to learn how their actions can be
brought under better control.
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