Anxiety and depression have been rising globally for decades, a tendency that has been worsened by the COVID-19 pandemic. A recent study revealed how researchers found new treatments to help alleviate this worldwide mental health burden.

A study was conducted by Frank Schroeder of the Boyce Thompson Institute and findings were published in Nature Chemical Biology.

First discovered in the 1930s, serotonin is a neurotransmitter that mediates myriad behaviours, such as feeding, sleep, mood and cognition. Drugs that alter serotonin levels are the main weapon to treat psychological conditions like anxiety and depression, as well as eating disorders.

As a simple model for neurobiology research, the microscopic roundworm Caenorhabditis elegans has been used extensively to study serotonin's role in regulating behaviour and food intake.

For many years, researchers thought that serotonin was made in an experimental model by one specific molecular pathway, and that serotonin was then quickly degraded. Schroeder's team and colleagues at Columbia University now demonstrated that both of those assumptions were not quite correct.

"We discovered a second, parallel biosynthetic pathway that accounts for about half of the total serotonin produced in our model system," said Schroeder.

The work began about three years ago when the researchers unexpectedly discovered an enzyme that converts serotonin into derivative compounds.

"Most people in the field thought serotonin is made and then quickly broken down, but we found that, instead, it is used as a building block for other compounds that are responsible for some of the serotonin's activity," explained Schroeder.

"So, we decided to start at the beginning and see how serotonin is made, and once it is made then how is it converted into these new molecules."

Jingfang Yu, a graduate student in Schroeder's lab and the first author of the paper, further showed that the new serotonin derivatives affect feeding behaviour.

"When the worms lack endogenous serotonin, they tend to move quickly across the bacteria food lawn on an agar plate, and turn infrequently to explore the food," Yu said.

"We found this behaviour can be alleviated by treating the worms with serotonin derivatives, suggesting these newly identified compounds contribute to effects previously attributed to serotonin."

The experimental model chosen for the study is an excellent model for studying serotonin because the compound's molecular signalling pathways are highly conserved across species, including in humans.

For example, the researchers showed that in the experimental subject, a large portion of serotonin is made in the gut, which is also the case in humans. Schroeder said there are hints that human serotonin is converted into metabolites.

"This research opens up the door for many more avenues of research in humans," said Schroeder, who is also a professor in the Department of Chemistry and Chemical Biology in the College of Arts and Sciences at Cornell University.

"Are the analogous metabolites important in humans? What is the role of one manufacturing pathway versus the other? How are these manufacturing pathways and metabolites important for human behaviours, like mental health and feeding behaviours?" he asked.

The researchers are currently exploring how the new serotonin derivatives affect behaviour in the experimental model and whether similar serotonin metabolites exist in humans.