NEUROBIOLOGY
The
basic cell of the brain and nervous system is called a neuron.
Neurons talk to each other by releasing neurotransmitters.
There are specific circuits of neurons in the brain that
use specific neurotransmitters, and studies over the last
fifty years have begun to identify which circuits and which
transmitters are involved in depression. Dopamine, norepinephrine,
and serotonin are some of the transmitters used in these
'mood circuits.' Antidepressant medications affect the amount
and duration of these transmitters. Note that they don't
actually affect neurons directly: rather they allow your
own natural transmitters to build up to higher levels.
Non-drug
interventions usually work by having you 'exercise' those
mood circuits in certain ways so that you jump-start your
brain into adjusting those transmitter levels. Some therapies
even cause your brain to create brand new circuits so that
depressive thoughts don't become so stifling. If the brains
of depressed people who took antidepressants are compared
with the brains of depressed people who had only psychotherapy,
the MRI (brain scan) images are very similar, providing
some evidence that there are multiple ways to cause the
same changes in the brain to relieve depression.
Scientific
studies have also found other biological mechanisms to be
related to depression including: changes in the endocrine
system (i.e., the system in which chemical messages are
sent through the blood, such as the thyroid gland), genetics
(e.g., one identical twin is much more likely to be become
depressed if the other has depression), parieto-occipital
oligodendroglial swelling (changes in the cells which protect
neurons in part of the brain), left frontal cortical and
subcortical hypoactivity (decreased activity in the part
of the brain just above your left eye), and changes to the
ventricles and basal ganglia (other structures of the brain).
Most
depression is considered 'psychiatric' meaning that it occurs
independently of other disease processes that may be at
work in the body. However, sometimes certain diseases and
drugs are responsible for the changes in the brain leading
to depression. Usually these non-psychiatric types of depression
have just one or two of the features of depression, for
example, just slowed movement but all else is normal. If
these medical problems are the cause, then if they are treated,
the depression will go away. Even so, the depression can
still be treated just like the 'regular' kind with certain
antidepressants and non-drug therapies.
Diseases
in any of the following organs may cause depression: kidneys,
heart, lungs, thyroid gland, adrenal gland, parathyroid
glands, pancreas Infections: pneumonia, mononucleosis, AIDS
Inflammation: lupus, rhuematoid arthritis Neurologic: epilepsy,
multiple sclerosis, Parkinson's disease, stroke,brain trauma.
In addition, many prescription drugs can cause depression
such as: steroids, oral contraceptives, propranolol, reserpine,
methyldopa Drugs of abuse: alcohol, marijuana, hallucinogens,
and amphetamine withdrawal, to name only a few.
