Depression (cont.)
What are the causes of depression?
Some types of depression run in families, indicating that a biological vulnerability to depression can be inherited. This seems to be the case especially with bipolar disorder. Studies have been done of families in which members of each generation develop bipolar disorder. The investigators found that those with the illness have a somewhat different genetic makeup than those who do not become ill. However, the reverse is not true. That is, not everybody with the genetic makeup that causes vulnerability to bipolar disorder will develop the illness. Apparently, additional factors, possibly a stressful environment, are involved in its onset and protective factors are involved in its prevention.
Major depression also seems to occur in generation after generation in some
families, although not as strongly as in bipolar I or II. Indeed, major
depression can also occur in people who have no family history of depression.
An external event often seems to initiate an episode of depression. Thus, a
serious loss, chronic illness, difficult relationship, financial problem, or any
unwelcome change in life patterns can trigger a depressive episode. Very often,
a combination of genetic, psychological, and environmental factors is involved
in the onset of a depressive disorder.
Nothing in the universe is as complex and fascinating as the human brain. The
over 100 chemicals that circulate in the brain are known as neurochemicals or
neurotransmitters. Much of our research and knowledge, however, has focused on
four of these neurochemical systems: norepinephrine, serotonin, dopamine, and
acetylcholine. In the new millennium, after new discoveries are made, it is
possible that these four neurochemicals will be viewed as the "black bile,
yellow bile, phlegm, and blood" of the 20th century.
Different neuropsychiatric illnesses seem to be associated with an
overabundance or a lack of some of these neurochemicals in certain parts of the
brain. For example, a lack of dopamine at the base of the brain causes Parkinson's
disease. Alzheimer dementia seems to be related to lower acetylcholine levels in
the brain. The addictive disorders are under the influence of the neurochemical
dopamine. That is to say, drugs and alcohol work by releasing dopamine in the
brain. The dopamine causes euphoria, which is a pleasant sensation. Repeated use
of drugs or alcohol, however, desensitizes the dopamine system, which means that
the system gets used to the drugs and alcohol. Therefore, a person needs more
drugs or alcohol to achieve the same high feeling. Thus, the addicted person
takes more substance but feels less and less high.
The different types of schizophrenia are associated with an imbalance of
dopamine (too much) and serotonin (poorly regulated) in certain areas of the
brain. Finally, the depressive disorders appear to be associated with altered brain serotonin and norepinephrine systems. Both of these neurochemicals may be lower in depressed people. Please note that abnormalities of these neurochemicals are "associated with" instead of "caused by," because we really don't know whether low levels of neurochemicals in the brain cause depression or whether depression causes low levels of neurochemicals in the brain.
What we do know is certain medications that alter the levels of
norepinephrine or serotonin can alleviate the symptoms of depression. Some
medicines that affect both of these neurochemical systems appear to perform even
better or faster. Other medications that treat depression primarily affect the
other neurochemical systems. The most powerful treatment for depression,
electroconvulsive therapy (ECT), is certainly not specific to any particular
neurotransmitter system. Rather, ECT, by causing a seizure, produces a
generalized brain activity that probably releases massive amounts of all of the
neurochemicals.
Women are twice as likely to become depressed as men. However, scientists do
not know the reason for this difference. Psychological factors also contribute
to a person's vulnerability to depression. Thus, persistent deprivation in
infancy, physical or sexual abuse, clusters of certain personality traits, and
inadequate ways of coping (maladaptive coping mechanisms) all can increase the
frequency and severity of depressive disorders, with or without inherited
vulnerability.
The effect of maternal-fetal stress on depression is currently an exciting
area of research. It seems that maternal stress during pregnancy can increase
the chance that the child will be prone to depression as an adult, particularly
if there is a genetic vulnerability. It is thought that the mother's
circulating stress hormones can influence the development of the fetus' brain
during pregnancy. This altered fetal brain development occurs in ways that
predispose the child to the risk of depression as an adult. Further research is
still necessary to clarify how this happens. Again, this situation shows the
complex interaction between genetic vulnerability and environmental stress, in
this case, the stress of the mother on the fetus.
Next: Postpartum depression »
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