Mental illness results from the combination of biological predisposition and experiences.
Both play an important role.
A solid understanding of both aspects is necessary for successful treatment.
Major depression - feeling sad and helpless everyday for weeks and includes the following characteristics (DSM-IV):
Feelings of worthlessness.
Feelings of hopelessness.
Similar symptoms can result from hormonal problems, head injuries, brain tumors, substance abuse, or other illnesses.
Absence of happiness is more reliable symptom than increased sadness.
Occurs at any age, but uncommon in children
Twice as common in women
10% lifetime prevalence.
Studies of twins and adopted children suggest a moderate degree of heritability.
Some of the genes associated with depression are also associated with anxiety disorders, ADD, OCD, substance-abuse disorders, bulimia, migraine headaches, irritable bowel syndrome, and several other conditions.
Risk is elevated among relatives of women with early-onset depression (before 30).
Predisposition depends on a variety of genes.
Effects of these genes have varied between studies
One gene identified controls the serotonin transporter protein.
controls the ability of the axon to reabsorb the neurotransmitter after its release.
Two “short forms” of the gene are associated with an increased likelihood of depression after stressful events.
May alters people’s reactions to stressful events or make them more sensitive to environmental influences
A few cases of depression are linked to viral infections.
Borna disease is a viral infection which may predispose people to depression
Illustrates that many different causes can lead to similar behavioral results
Postpartum depression is depression after giving birth.
Affects about 20% of women and most recover quickly
More common among women who have suffered depression at other times.
May be associated with a drop in estradiol and progesterone levels .
Testosterone drop in men also associated with increased probability
Depression is also associated with the following brain activity:
Decreased activity in the left prefrontal cortex.
Increased activity in the right prefrontal cortex.
Many drugs used to treat psychiatric disorders discovered by accident
Categories of antidepressant drugs include:
Selective serotonin reuptake inhibitors.
Tricylclics - operate by blocking transporter proteins that reabsorb serotonin, dopamine, and norepinephrine into the presynaptic neuron after release.
Examples: imipramine (Tofranil)
Also block histamine receptors, acetylcholine receptors, and certain sodium channels.