Causes of Mood Disorders – Serotonin, Dopamine, Norepinephrine

Today, I was watching a Comcast On Demand program about the causes of bipolar. I thought I’d watch and see how ridiculous it was because obviously, no one knows the cause of bipolar disorder.

However, the spot had some interesting information on the brain, neurotransmitters and bipolar disorder, which I then transcribed so I could share it with you. (Yes, I really did transcribe the whole thing.)

It’s in fairly layperson terms, so give it a look. At the bottom is a bit more information about dopamine, norepinephrine, and serotonin. This, unfortunately, is not in layperson terms, but is interesting nonetheless.

Brain Chemistry and Bipolar Disorder

And for the info:

…but research has shown that chemical imbalances in the brain play an especially key role in the onset of the disease. Every adult has more than 90 billion brain cells, or neurons. These neurons communicate with each other through chemical messengers called neurotransmitters. Neurotransmitters help control a range of bodily functions such as thinking, reasoning, and mood. But when they don’t function properly then problems can occur.

Here’s how neurotransmitters work, each neurons is composed of an axon, a dendrite, and cell body. When a neuron fires, an electrical signal is sent to the axon, and down a long slender tube that functions like an antennae. At the end of the axon the signal is transferred to the neurotransmitters. These neurotransmitters then travel across a synapse, or gap, to a dendrite of another neuron which receives the chemical messages. Once the process is complete the neurotransmitters are pumped back into the releasing neuron.

Under normal circumstances, just the right amount of a neurotransmitter is sent across the gap to communicate with other neurons, but in cases of bipolar disorder levels of certain neurotransmitters are abnormally high or low which experts believe can trigger mood abnormalities. For example, bipolar depression has been linked to low levels of serotonin in the synaptic gap. Serotonin is a neurotransmitter that helps regulate moods. Manic episodes have been associated with high levels of norepinephrine; the neurotransmitter that contributes to our fight or flight response. And too much dopamine, a neurotransmitter effecting emotions and perceptions, is linked to psychotic symptoms such as hallucinations.

Breakthroughs in diagnostic imaging have revealed that the brain structure of those suffering from bipolar disorders also differs from those of healthy individuals. Using advanced MRI and PET scanning technologies, experts now have evidence that experiences of sever episodes of bipolar depression can lead to changes in different parts of the brain. For example, the brain has two hypocampii, each located in the temporal lobes. One of the functions of the hippocampus is to help control learning, emotions, and memory. In some bipolar patients the hippocampus appears to shrink over time. Other areas of the brain’s temporal regions may shrink as well.

Since bipolar disorder often runs in families, scientists are trying to identify the specific genes that cause the condition. But genes are likely not the only explanation. Studies on identical twins reveal that if one twin develops bipolar, the other twin has an 80% chanced of developing bipolar as well. This suggests that while genes are a primary cause, other factors may also be needed for the disease to manifest itself. People born with the possibility of bipolar may find that stressful events like divorce, job loss or emotional strain can trigger the illness…

Serontonin, the Brain and Bipolar Disorder

Serotonin can also do the following:

1. It gives us self-confidence, a feeling of safety and security.
2. It causes us to feel sleepy.
3. It increases our appetites.

The part of the brain where it does each of these 3 things is a different part of the brain from the part where the other 2 things occur. Thus, for example, increasing serotonin in the part of the brain where self-confidence is will increase your self-confidence, but not your sleepiness. Unfortunately, we have no medications to increase only the serotonin in one part of the brain. This explains why medications to increase serotonin in the brain can also cause increased appetite and sleepiness.

Medications which increase serotonin in the brain (SSRI’s such as citalopram, escitalopram, fluoxetine, paroxetine, and sertraline and SNRI’s such as venlafaxine and duloxetine) give us more self-confidence, and a feeling of safety and security.

By the way, serotonin also exists in our gastrointestinal tracts. In this location, it stimulates digestion. This is why such medications can cause gastrointestinal upset. But they can also help constipation.

Norepinephrine, the Brain and Bipolar Disorder

Norepinephrine is a catecholamine with dual roles as a hormone and a neurotransmitter.

As a stress hormone, norepinephrine affects parts of the brain where attention and responding actions are controlled. Along with epinephrine, norepinephrine also underlies the fight-or-flight response, directly increasing heart rate, triggering the release of glucose from energy stores, and increasing blood flow to skeletal muscle.

However, when norepinephrine acts as a drug it will increase blood pressure by its prominent increasing effects on the vascular tone from α-adrenergic receptor activation. The resulting increase in vascular resistance triggers a compensatory reflex that overcomes its direct stimulatory effects on the heart, called the baroreceptor reflex, which results in a drop in heart rate called reflex bradycardia.

Dopamine, the Brain and Bipolar Disorder

Dopamine

Dopamine has many functions in the brain, including important roles in behavior and cognition, voluntary movement, motivation and reward, inhibition of prolactin production (involved in lactation), sleep, mood, attention, and learning.

A common hypothesis, though not uncontroversial, is that dopamine has a function of transmitting reward prediction error. According to this hypothesis, the phasic responses of dopamine neurons are observed when an unexpected reward is presented. These responses transfer to the onset of a conditioned stimulus after repeated pairings with the reward. Further, dopamine neurons are depressed when the expected reward is omitted. Thus, dopamine neurons seem to encode the prediction error of rewarding outcomes. In nature, we learn to repeat behaviors that lead to maximize rewards. Dopamine is therefore believed to provide a teaching signal to parts of the brain responsible for acquiring new behavior. Temporal difference learning provides a computational model describing how the prediction error of dopamine neurons is used as a teaching signal.

 

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