Introduction: The Science Behind Depression

  1. Neurotransmitters
  2. Genetics
  3. Limbic System


Communication from our nervous system to other parts of the body occurs in the form of electrical impulses. A cell called a neuron is what carries these messages. Our brain is full of over 100 billion of these neurons.

  1. The cell body is what directs all the activity within the neuron
  2. The dendrites receive information from other neurons
  3. The axon is was transmits messages from the cell body of its neuron to the dendrites of other neurons or other body tissues, such as muscles.
  4. The myelin is a protective covering that covers most of the neurons and helps nerve signals travel much faster and farther.
  • Acetylcholine enhances memory and is involved in learning and recall.
  • Serotonin helps regulate sleep, appetite, and mood and inhibits pain. Some depressed people have reduced serotonin transmission. Low levels of serotonin can trigger a drop in norepinephrine levels, which then leads to depression.
  • Norepinephrine constricts blood vessels, raising blood pressure. This may trigger anxiety and be involved in some types of depression. It also seems to help determine motivation and reward.
  • Dopamine is essential to movement. It also influences motivation and plays a role in how a person perceives reality. Problems in dopamine transmission have been associated with psychosis, a severe form of distorted thinking characterized by hallucinations or delusions. It’s also involved in the brain’s reward system, so it is thought to play a role in substance abuse.
  • Glutamate is a small molecule believed to act as an excitatory neurotransmitter and to play a role in bipolar disorder and schizophrenia. Lithium carbonate, a well-known mood stabilizer used to treat bipolar disorder, helps prevent damage to neurons in the brains of rats exposed to high levels of glutamate. Other animal research suggests that lithium might stabilize glutamate reuptake, a mechanism that may explain how the drug smooths out the highs of mania and the lows of depression in the long term.
  • Gamma-aminobutyric acid (GABA) is an amino acid that researchers believe acts as an inhibitory neurotransmitter. It’s known to help remove anxiety.


A person who has a relative with depression is almost five times as likely to develop it compared to someone who doesn’t have a relative with depression. Scientists also believe that approximately 40% of people with depression can trace it back to family history. That means there is a heritability genetic component to depression.

Chromosome 3p25–26 (Jermey)

The chromosome 3p25–26 (or Jermey) was found in more than 800 families with recurrent depression. The chromosome contains up to 40 genes and is believed to contain the genes contributing to depression.

Genetic Variant 5-HHTLPR (Kendall)

Another review of 19 studies found a link between a different genetic variant called 5-HHTLPR (or Kendall) and MDD.

inside the red circle is the synaptic cleft

Gaps + Next Steps

A lot of the research done in this area is limited and fresh. We need to dive deeper into the chromosome and genetic variant mentioned above but we also need to continue looking for other possible hereditary links.

The Limbic System

The limbic system is the part of the brain involved in our behavioural and emotional responses. This is especially focused on survival behaviours.



The amygdala is part of the limbic system, a group of structures that’s responsible for the detection of threats and fear-related behaviours in response to threatening or dangerous stimuli.


The hippocampus is responsible for processing long-term memory and recollection. It works together with the amygdala to recall fearful moments and respond accordingly.



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