Serotonin-Mediated Avoidance and Immune Suppression in Caenorhabditis elegans Exposed to Sodium Arsenite

Pathogen avoidance behavior is widespread across the animal kingdom and plays an important role in animal survival in natural environments. As a free-living nematode, Caenorhabditis elegans is exposed to various microorganisms and toxic chemicals in the soil, including pathogenic bacteria and chemical toxins. C. elegans can effectively avoid pathogenic bacteria, thereby minimizing the risk of infection. However, it remains unclear whether it also exhibits avoidance behavior in response to toxic substances such as sodium arsenite. In this report, we found that as the sodium arsenite concentration in the environment increased, the arsenic content in C. elegans also increased, leading to an avoidance response. Further investigation revealed that deletion of the serotonin synthesis gene tph-1 significantly suppressed this avoidance behavior. Moreover, the expression level of TPH-1 protein in ADF neurons was significantly upregulated. Our data indicate that C. elegans exhibits a serotonin-mediated behavioral avoidance response to sodium arsenite. Additionally, we observed that the immune system of C. elegans was suppressed following sodium arsenite exposure, likely as an adaptation to the adverse environment. This study provides new insights into the strategies of C. elegans in response to toxic environmental conditions.