Date of Completion


Embargo Period



Microbiome, neurotransmitter, gut-brain axis, irritable bowel syndrome, emotional distress.

Major Advisor

Dr. Xiaomei Cong

Associate Advisor

Dr. Angela Starkweather

Associate Advisor

Dr. Wendy Henderson

Field of Study



Doctor of Philosophy

Open Access

Campus Access


Evidence highlights the comorbidity between emotional distress and Irritable bowel syndrome (IBS) through the brain-gut microbiome axis. However, the underlying mechanism is largely unknown, and limited studies have addressed the role of the gut microbiome and the neurotransmitters in this comorbidity. The study aimed to identify biomarkers of emotional distress (neurotransmitter levels and gut microbiome patterns) in individuals with IBS.

In this cross-sectional study, 28 individuals with IBS and ten healthy controls were assessed for their level of emotional distress, including anxiety and depression. Plasma neurotransmitters(serotonin, norepinephrine) were tested using the enzyme-linked immunosorbent assay (ELISA) method. Fecal samples were collected, and gut microbiome profiles were examined using 16S rRNA Illumina sequencing. The microbial analyses comprised of alpha and beta diversity as well as bacterial composition. The Pearson correlation used to investigate the relationship between neurotransmitters levels and bacterial profile. The emotional distress was significantly different between IBS and healthy control groups. However, the levels of the neurotransmitters, including serotonin and norepinephrine, were not different between the two groups. While the bacterial profiles differed between IBS and healthy controls, there was no significant association between neurotransmitter levels and bacterial profile except negative correlation between plasma serotonin levels and total observed species (sobs) as well as positive correlation association between plasma serotonin levels and beta diversity.

The present study demonstrated that the bacterial composition of fecal samples of participants with IBS was different from healthy controls. While there was no difference in neurotransmitter levels between study groups, the correlation between gut microbiome diversity and plasma serotonin levels suggests that the pattern of the gut microbiome may impact the neurotransmitter levels. Further studies are required to specify the involved gut microbiota in the modulation of the neurotransmitter levels.

Available for download on Saturday, May 03, 2025