Researchers have shown that rodents without a specific serotonin receptor manage to overcome their fear more quickly than those who have it. This discovery could help develop new treatments for post-traumatic stress disorder or anxiety pathologies.
- Post-traumatic stress disorder is a psychiatric disorder that occurs after a traumatic event.
- Serotonin plays a key role in the onset and unlearning of fear and anxiety.
Serotonin is involved in the development of fear and anxiety. Scientists from the Ruhr University in Bochum (Germany) sought to understand the role of this neurotransmitter in extinction learning, i.e. the “unlearning fear”.
Serotonin and fear: work carried out on mice
To better understand the link between the neurotransmitter and fear, the researchers looked at genetically modified mice that lack a serotonin receptor called the 5-HT2C receptor.
The latter learned in one day to associate a certain sound with a light, but unpleasant electrical stimulus. “As a result of this learning process, the next day they showed a fear response characterized by a motionless pause as soon as the sound was played, what we call ‘freezing'”explains Katharina Spoida from the German University’s Department of General Zoology and Neurobiology.
The next step was to repeatedly play the noise without the electrical stimulation. “Interestingly, we noticed that knockout mice learned much faster than sound does not predict the fear stimulus than mice without this specific genetic modification”explains the expert. “Therefore, it appears that the absence of the serotonin receptor provides an advantage for extinction learning.”she continues in her article.
Absence of the serotonin receptor: 2 areas of the brain affected
In addition, animals lacking serotonin 5-HT2C receptors showed changes in their neuronal activity in two different brain areas:
- a specific sub-region of the dorsal raphe nucleus (DRN): this is generally the main site of serotonin production in the brain;
- the bed nucleus of the stria terminalis (BNST): this area plays a central role in the expression of anxiety.
“In knockout mice, we first found increased basal activity in some serotonin-producing cells of the dorsal raphe nuclei. In a later step, we showed that the absence of the receptor also alters neuronal activity in two subnuclei of the BNST, which ultimately supports extinction learning”confirms scientist Sandra Süß, who is also leading the work.
The research results also indicate a link between the two brain regions, leading scientists to speculate that an interaction is important for enhancing extinction learning.
A useful discovery for the treatment of post-traumatic stress disorder
“There are already drugs in clinical use that regulate the amount of serotonin available, called selective serotonin reuptake inhibitors (SSRIs)”emphasizes Katharina Spoida.
“Taking these drugs over a prolonged period of time makes the relevant receptor less responsive to serotonin, as in our knockout model. Therefore, we speculate that the changes we have described could be essential for the positive effect of SSRIs. “adds his colleague Sandra Süß.
According to the researchers, their work could help develop more targeted treatments for patients with post-traumatic stress disorder.
