The Role of Serotonin in Anxiety-like Behavior in Planaria

Stress and anxiety can take a toll on the human body by affecting one’s emotional and/or physical health. For some, it manifests into a disorder where persistent and excessive stress interferes with daily activities. Serotonin, or 5-hydroxytryptamine (5-HT), is a neurotransmitter that regulates various activities in the body such as behavior and mood. It is the primary treatment target for many psychiatric and neurological disorders associated with decreased central nervous system (CNS) such as major depressive disorder, anxiety disorder, PTSD, etc. Despite extensive studies on serotonin (5-HT), its mechanisms and several subtypes are still poorly understood. There is strong evidence to suggest that 5-HT1A and 5-HT2A-C are closely related to anxiety-like behavior. In this study, I used planaria as an animal model to determine the role of serotonin in anxiety-like behavior due to their similarities in serotonin systems to rodents. With the standard behavioral assay, the planarian light/dark test (PLDT), I used 5-HT, AS-19 (5-HT7 agonist), 8-OH-DPAT (5-HT1A agonist), and WAY-100635 (5-HT1A antagonist) to investigate how serotonin affects light avoidance behavior in planaria, mimicking rodent studies. I expect AS19 and WAY-100635 will decrease light exploration while 8-OH-DPAT will increase light exploration. With 5-HT, effects on light avoidance were observed at 1µM and 10µM compared to the control. Ongoing experiments involve using AS-19, 8-OH-DPAT, and WAY-100635 to assess potential effects in light exploration. This study can help researchers identify ways to manipulate specific serotonin receptors to potentially develop new drugs or better treatment plans designed for people with anxiety disorders. NIH Bridges to the Doctorate This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.