A neurotransmitter used in the treatment of mental health disorders has unintended consequences on auditory perception.
Tinnitus causes a persistent ringing in the ears. For some people it is irrelevant, but for others it can cause suffering and anxiety. The condition is common throughout the world, affecting even 14% of the population, with many cases considered serious.
In new, published last week in Proceedings of the National Academy of Sciencesresearchers used a mouse model to study the effects of serotonin on the brain.
According to , scientists observed that higher levels of serotonin are associated with more intense behavioral signs.
“People with tinnitus should work closely with their doctor to find a medication regimen that provides a balance between relieving psychiatric symptoms, such as depression and anxiety, and minimizing the experience of tinnitus,” says study co-author, Laurence Trussell.
This study highlights the importance of clinicians recognizing and validating patients’ reports of increased tinnitus associated with medication.
The medicines in question include selective serotonin reuptake inhibitorsor SSRI, a widely used class of antidepressants. These treat moderate to severe depression and anxiety by increasing serotonin levels in the brain.
“Now, using rats, we have discovered a brain circuit involving serotonin that goes directly to the auditory system. It is capable of inducing effects similar to tinnitus, however, when you deactivate the circuit, it is possible to alleviate tinnitus,” says Trussell.
The researchers used the optogeneticsa technique that uses fiber optic to send light to the brain, allowing them to precisely activate serotonin-producing neurons. Then they measured the mice’s response using a modified hearing test.
“When you encourage serotonergic neuronswe can see that this stimulates activity in the auditory region of the brain”, reveals Trussell.
“We also observed that the animals behaved as if they were hearing tinnitus. In other words, they are producing symptoms that we would expect to be felt in humans,” he adds.
These results correspond with reports from some patients who notice that their tinnitus worsens when they take medications that increase serotonin, including SSRIs.
“It may be possible to develop specific drugs for brain cells or regions that direct the increase of serotonin in some brain regions, but not others. In this way, it may be possible to separate the beneficial and important effects of the antidepressant from the potentially harmful effects on hearing”, concludes the scientist.
