What Causes Bipolar Disorder?

Bipolar disorder is a serious psychiatric illness that causes fluctuations in mood between depression and mania. Many experts now believe that bipolar disorder is caused by altered levels of neurotransmitters in the brain, but it is obvious to most that there is no single cause for the disorder and that many factors work together to produce the illness in most people. The three reasons most commonly believed to cause bipolar disorder are explained below.

Neurotransmitters:

Neurotransmitters are chemical messengers that enable nerve impulses to be transmitted from one neuron to another. The level of certain critical neurotransmitters is strongly linked to mood disorders.

Nerve impulses are transmitted from neuron to neuron across synapses, which are junctions where the axon (or transmitting end) of one neuron is next to the dendrites (or receiving end) of the receptor neuron. Depression is believed to be caused by a deficit of specific neurotransmitters (norepinephrine, dopamine, or serotonin) at brain synapses, whereas mania is thought to be caused by an oversupply of these substances.

The neurotransmitters thought to play the most active role in bipolar and other psychiatric disorders are serotonin, dopamine, and norepinephrine.

Serotonin: Also known as 5-hydroxytryptamine or 5-HT, Serotonin controls sleep, mood, some types of sensory perception, body-temperature regulation, and appetite. It also affects the rate at which hormones are released, and has something to do with inflammation.

Dopamine: This neurotransmitter helps control body movements and patterns of thought, and also regulates how hormones are released.

Norepinephrine: Used by both the central nervous system and the peripheral sympathetic nervous system, it governs arousal, the "fight or flight" response, anxiety, and memory.

The use of medications that affect the levels of these neurotransmitters in the treatment of bipolar disorder have proved to be effective for most people.

Increased Brain Activity:

New brain-imaging techniques using MRI and PET machines allow researchers to take pictures of the bipolar brain while it is at work, and to study its structure and activity. There is evidence from imaging studies that the brains of people with bipolar disorder may differ markedly from the brains of those without the disorder.

A study published in the American Journal of Psychiatry reports that "in those with bipolar disorder, two major areas of the brain contain 30 percent more cells that send signals to other brain cells." This report theorizes that "the extra signal-sending cells may lead to a kind of overstimulation, which makes sense considering the symptoms of bipolar disorder."

Genetics:

Most people that suffer from bipolar disorder have a positive family history for mood disorders, suicide, and/or alcohol and drug abuse - causing researchers to look for specific genes that might be involved in the development of the disorder.

Intensive effort is currently being put into identifying the genes involved in bipolar disorder. One candidate gene which might cause bipolar codes for the serotonin transporter. Serotonin (a neurotransmitter) is involved in a variety of behaviors including sleep, moods, and activity, all of which are affected to some degree in bipolar disorder.

Recent studies done of identical twins indicate that both genes and other factors must play a role in the development of bipolar disorder. If bipolar disorder were caused entirely by genetics, then the identical twin of someone suffering from bipolar would always develop the illness as identical twins share all of the same genes. Research has shown that this is not always true, and that even in cases where both twins develop the disorder the onset and course of symptoms is often very different.

It is therefore believed that social and developmental factors may also contribute to causing depression or affect the course of treatment for bipolar disorder.