The gene of depression:
Worldwide, depression affects more than 300 million people a year and almost 800,000 die by suicide every year, being the second cause of death among people between 15 to 29 years. Beyond that, depression destroys the quality of life of tens of millions of patients and their families and, although environmental factors play a role in many cases of depression, genetics is also crucially important.
A subset of neurons is the key in the brain reward circuit:
This region plays a central role in the “reward circuit” of the brain. When a person eats a delicious meal, has sex, drinks alcohol, or experiences any other kind of pleasant experience, the neurons in the nucleus accumbens are activated, letting you know that the experience is activating the appropriate buttons. In depression, any kind of enjoyment becomes difficult or impossible; a symptom that is known as anhedonia, which in Latin means inability to experience pleasure.
The researchers focused on a subset of neurons in the nucleus accumbens called D2 neurons, which respond to the neurotransmitter dopamine, playing a central role in the reward circuit. These experts studied mice susceptible to depression; when they were subjected to social stress – more exposure, more aggressive rodents – they tend to withdraw and exhibit behavior that indicates depression, such as social withdrawal and lack of interest in the foods they normally enjoy.
It was found that when these animals were subjected to chronic social stress, the levels of the Slc6a15 gene in the D2 neurons of the nucleus accumbens were markedly reduced. The researchers also studied mice in which the gene had been reduced in D2 neurons. When the rodents were subjected to stress, they also showed signs of depression; But when the researchers raised the levels of Slc6a15 in the D2 neurons, the mice showed a resilient response to stress.