Clues to the biology of mood disorders have stemmed mainly from the drugs used to treat them. Manic depression is most commonly treated with compounds containing the element lithium. Most drugs for major depression affect the brain chemicals serotonin or norepinephrine. Prozac, for example, attacks depression by blocking the molecules that clean serotonin out of the nerve cell connections known as synapses. That leaves more serotonin around, leading ultimately to an improved mood.
Manic depression is even more difficult to understand.
The evidence suggests that lithium operates inside the cell, perhaps affecting the internal cell molecules called G proteins. G proteins are key players in the cellular messaging systems that tell genes what chemicals to produce. Drevets and colleagues have shown, for example, that depressed patients have abnormally high blood flow in the amygdala, a brain region important for emotional behavior. Anxiety disorders Major depression often accompanies another major group of mental illness, the anxiety disorder, among which the most prominent are panic disorder and obsessive-compulsive disorder. In panic disorder, more than half the victims also suffer from major depression.