The researchers found stopping the neurons from releasing noradrenaline made the animals systematically susceptible to depression when exposed to chronic stress.
The new study - the first to find such a link - is the work of researchers from McGill University in Montréal, Canada, who report their findings in the journal Nature Neuroscience.
Stressful life events - such as the death of a loved one, serious accident or losing one's job - can trigger major depression, a common mental disorder that is characterized by loss of interest or pleasure, feelings of guilt or low self-worth, disturbed sleep or appetite, feelings of tiredness, sadness and poor concentration.
Scientists believe a deciding factor in whether traumatic events trigger depression or not is resilience. However, the biology of resilience is somewhat of a mystery and there is still a lot to learn about it.
We already know that a small part of the midbrain called the ventral tegmental area (VTA) is rich in dopamine-releasing neurons that play an important role in vulnerability to stress and depression.
Inability to release noradrenaline made animals susceptible to depression
By mimicking stressful life events in animal models, the team behind the new study confirmed that increased release of dopamine in the neurons of the VTA corresponds to depression.
- Globally, an estimated 350 million people suffer from depression
- Despite effective treatments, fewer than half of this number receive them
- At its worst, depression can lead to suicide, the second leading cause of death in 15-29-year-olds.
They then showed how a second type of neuron - that releases noradrenaline and is located in another part of the brain called the locus coeruleus - controls the activity of the dopamine neurons.
Senior author Bruno Giros, a professor in the department of psychiatry, says:
"It is this control that steers the body's response toward resilience or toward vulnerability to depression."
Noradrenaline is a neurotransmitter molecule already known to be involved in emotional regulation, sleep and mood disorders.
The team used a combination of approaches to activate and switch off the neurons involved. The approaches included pharmacological, genetic and optogenetic (where genes in the neurons are switched on by a beam of light) techniques.
They found that animals that cannot release noradrenaline are systematically susceptible to depression when exposed to chronic stress.
However, they also found the condition is reversible: when the neurons were stimulated to produce more noradrenaline, the animals became more resilient to stress and less susceptible to depression.
The team believes the discovery is a breakthrough that could lead to new depression treatments, as Prof. Giros explains:
"Beyond this discovery about the brain mechanisms involved in depression, our results help explain how adrenergic drugs may work and could be used to treat major depression."
Meanwhile, Medical News Today recently learned about a medical innovation that suggests immersive virtual reality may help patients with depression. It appears that when embodied in an avatar, patients learn how to show more compassion toward themselves and are less self-critical, a trait that can be common in people with depression.