Serotonin was supposed to be our friend. Though often referred to by science blogs as the "happiness hormone," in recent years, serotonin's role in making us happy has come into question.
If you've ever taken selective serotonin reuptake inhibitors (SSRIs)—drugs like Prozac and Zoloft that boost your levels of serotonin—you probably know the results can actually be a mixed bag, particularly in the first few weeks. In my case, sometimes I feel like my life force is being tickled by God, but then other times I'm sure my bedroom walls are about to cave in and crush me.
A new study out of the University of North Carolina at Chapel Hill, attempts to get to the root of this problem. Using lab mice, the experiment investigated the cause of the roller-coaster-like serotonin ramp-up period for SSRI. The researchers found something puzzling, confirming that serotonin activates circuitry in a certain area of the brain that's directly tied to fear and anxiety.
According to Thomas Kash, a professor of pharmacology at University of North Carolina School of Medicine, and one of the co-authors of the study, researchers may need to focus on this part of the brain—called the BNST, which stands for bed nucleus of the stria terminalis—if they want to understand anxiety.
"This highlights the important role of this structure, the BNST, in anxiety disorders, adding to a growing body of literature suggesting that this may be a potent regulator of different types of anxiety behavior," Kash told VICE.
That's partly because by watching what was going on in the BNST, Kash's research team demonstrated how serotonin-boosting drugs may be tied to anxiety—the exact thing SSRIs are used to treat in the first place. Even more unsettlingly, the researchers also found that naturally-occurring serotonin might play a role in activating fear systems as well.
To get to these findings, researchers zapped the paws of the lab mice with electricity, and watched a specific area of the brain produce serotonin and deliver it to the BNST. They found that when the flow of serotonin was increased, so were the mouse's anxiety symptoms. Applying Prozac to the BNST also increased anxiety.
Sure, the mice were better able to cope with their paws being shocked, so serotonin was working as advertised. But the experiment essentially confirmed that serotonin was making the recently-zapped mice anxious.
It's a reminder that calling serotonin a "happiness hormone" may give the wrong impression. In fact, according to Skirmantas Janusonis, an associate professor of neuroscience at the University of California, Santa Barbara, who studies the brain serotonin system, that characterization only scratches the surface of what serotonin actually does.
"The entire brain is embedded in a dense meshwork of serotonin-releasing fibers, but only a small part of the brain is directly involved in the feelings that we can consciously access—be it sadness or joy," Janusonis told VICE. "SSRIs hit the entire system indiscriminately."
According to Kash, the results found in the lab mice could easily translate to humans, who share the BNST brain region. In human imaging studies, he said, "activation of the BNST has been associated with anxiety and dread in human imaging studies."
"It is plausible that when we give people acute SSRI, this region is recruited to drive anxiety in some people," Kash said. "However," he added, "we will not know until somebody tests this directly."
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