The 5-HT₃ Receptor Affects Rotavirus-Induced Motility

Rotavirus infection is highly prevalent in children, and the most severe effects are diarrhea and vomiting. It is well accepted that the enteric nervous system (ENS) is activated and plays an important role, but knowledge of how rotavirus activates nerves within ENS and to the vomiting center is lacking. Serotonin is released during rotavirus infection, and antagonists to the serotonin receptor subtype 3 (5-HT₃ receptor) can attenuate rotavirus-induced diarrhea. In this study, we used a 5-HT₃ receptor knockout (KO) mouse model to investigate the role of this receptor in rotavirus-induced diarrhea, motility, electrolyte secretion, inflammatory response, and vomiting reflex. The number of diarrhea days (P = 0.03) and the number of mice with diarrhea were lower in infected 5-HT₃ receptor KO than wild-type pups. In vivo investigation of fluorescein isothiocyanate (FITC)-dextran transit time showed that intestinal motility was lower in the infected 5-HT₃ receptor KO compared to wild-type mice (P = 0.0023). Ex vivo Ussing chamber measurements of potential difference across the intestinal epithelia showed no significant difference in electrolyte secretion between the two groups. Immediate early gene cFos expression level showed no difference in activation of the vomiting center in the brain. Cytokine analysis of the intestine indicated a low effect of inflammatory response in rotavirus-infected mice lacking the 5-HT₃ receptor. Our findings indicate that the 5-HT₃ receptor is involved in rotavirus-induced diarrhea via its effect on intestinal motility and that the vagus nerve signaling to the vomiting center occurs also in the absence of the 5-HT₃ receptor. IMPORTANCE The mechanisms underlying rotavirus-induced diarrhea and vomiting are not yet fully understood. To better understand rotavirus pathophysiology, characterization of nerve signaling within the ENS and through vagal efferent nerves to the brain, which have been shown to be of great importance to the disease, is necessary. Serotonin (5-HT), a mediator of both diarrhea and vomiting, has been shown to be released from enterochromaffin cells in response to rotavirus infection and the rotavirus enterotoxin NSP4. Here, we investigated the role of the serotonin receptor 5-HT₃, which is known to be involved in the nerve signals that regulate gut motility, intestinal secretion, and signal transduction through the vagus nerve to the brain. We show that the 5-HT₃ receptor is involved in rotavirus-induced diarrhea by promoting intestinal motility. The findings shed light on new treatment possibilities for rotavirus diarrhea.