The functions of the human brain, including emotions, are regulated by neurotransmitters that pass chemical messages around the body. Depression, for example, has been linked to a chemical imbalance in mood-regulating neurotransmitters like serotonin and dopamine. This imbalance may be the result of a genetic disorder, drug abuse, a traumatic life event, or – as many researchers believe – a combination of different factors.
Here we look at the chemistry of depression in more detail, along with the potential impact of chemical imbalances in the brain and the role of genetics.
In this post:
What is depression?
Depression is not simply feeling sad or a bout of the blues. Rather, it’s characterised by lingering feelings of severe despondency and dejection. A person who is depressed may feel a loss of hope, purpose, or meaning in their life. The condition is sometimes triggered by a traumatic or stressful event, such as bereavement or the end of a romantic relationship.
Depression affects everyone differently and the symptoms can vary from mild to severe. Some people who are depressed may become withdrawn, irritable, and stop looking after themselves properly. In severe cases, a person may even develop suicidal thoughts.
The underlying cause or trigger might be different from one case to another, but the same chemicals are usually involved. As we explain below, neurotransmitters such as serotonin and dopamine have important roles in regulating human mood and behaviour.
What chemical imbalances cause depression?
Some of the most important chemicals, or neurotransmitters, that can influence our emotional state and mental wellbeing are serotonin, dopamine, endorphins, oxytocin, and norepinephrine.
Dopamine is often called the happiness or ‘feel-good’ neurotransmitter, while oxytocin is known as the love hormone. Serotonin helps to regulate sleep and norepinephrine (also called noradrenaline) is involved in the body’s flight-or-fight response.
Together, these neurotransmitters modulate our feelings of happiness and sadness, as well as our response to stress. Some experts believe low levels of dopamine and serotonin can trigger sadness that may lead to depression, especially if it’s exacerbated by stress. In these cases, antidepressant medication and mood stabilisers may help to redress the chemical imbalances that could be contributing to depression, although some researchers dispute this claim.
Below we explore two of the most common brain chemical conditions that regulate mood. They can potentially either trigger or prevent depression, depending on the circumstances.
1. Decreased levels of serotonin
Depression has historically been linked to low levels of serotonin. Some studies have shown that serotonin can influence our mood and that people with normal levels of serotonin are generally more emotionally stable. They often tend to be more focused and not easily irritable.
On the other hand, those with low levels of serotonin may be more likely to fall into depression and suffer from poor mental health. This is the reason why many of the psychiatric medications used in treating depression and other mood disorders are chemically designed to increase the level of serotonin in the brain.
What is serotonin?
Serotonin (otherwise known by its IUPAC name 5-hydroxytryptamine) is a neurotransmitter with a single amino group. It has the chemical formula C₁₀H₁₂N₂O. Serotonin has several functions such as modulating mood and regulating memories. It also plays a role in various physiological processes including vasoconstriction.
2. Increased levels of monoamine neurotransmitters
Some people believe increased levels of certain types of monoamine neurotransmitters can potentially trigger or prevent depression. For example, elevated levels of dopamine result in a sense of euphoria and wellbeing.
However, if the trigger for this dopamine spike is something artificial like drugs or alcohol, a person can eventually develop dopamine tolerance. This means they’ll need to seek higher doses of pleasure-seeking triggers to experience the same level of euphoria. Without this pleasure, they may become lethargic and depressed. This is how addiction occurs.
What is monoamine?
Monoamine neurotransmitters are brain chemicals and hormones that regulate mood and other mental functions. As the name suggests, they have an amino group per molecule. The amino group is attached to an aromatic ring. Examples of monoamine neurotransmitters include serotonin, dopamine, and norepinephrine.
Is depression genetic?
Depression can occur as a result of a traumatic or stressful event, such as abuse, bereavement, unemployment, or a relationship breakdown. Anyone, young or old, can become depressed if there’s a trigger. However, genetics may play a role in those who suffer from a major depressive disorder. These kinds of conditions are usually associated with other types of psychiatric illnesses, like bipolar disorder and schizophrenia.
Many experts think the genetic link to depression is a combination of various genes rather than one specific gene. Some of the genes that are most likely to be involved in someone developing depression are the following:
- Receptor genes for dopamine (DRD3, DRD4)
- Receptor genes for serotonin (HTR1A, HTR2A, HTR1B, HTR2C)
- Receptor gene for noradrenalin (SLC6A2)
- The gene for producing dopamine (SLC6A3)
Based on a report published by the World Health Organisation, around 280 million people are affected by depressive disorders worldwide. Studies on families and twins have also shown the strong genetic link and inheritability of depressive disorders.
Does depression permanently change brain chemistry?
If left untreated, there’s evidence to suggest depression can permanently change your brain chemistry. This is especially true for those who have a genetic predisposition and/or who have an addiction.
The way genes are expressed and the way the receptors become highly tolerant to certain types of neurotransmitters can affect how their brain works. This could be one of the reasons why depression can be difficult to treat in some people.
Summary
Various neurotransmitters, or chemical messengers, in the brain, regulate our mood and emotional state. Some experts believe an imbalance in these chemicals can contribute to depression, although in reality there may be several causes. While stressful or traumatic life events can trigger depression, for some people genetics play a role, too. Studies suggest long-term depression may permanently change your brain chemistry and how the receptors work.
