Superoxide-imbalance pharmacologically induced by Rotenone triggers behavioral, neural, and inflammatory alterations in the Eisenia fetida earthworm

Background: The inflammatory theory of depression has been tested from epidemiological and experimental investigations. Some studies have suggested that mitochondrial dysfunction superoxide imbalance could increase the susceptibility to chronic stressful events, contributing to the establishment of chronic inflammation and the development of mood disorders. If this premise is true, mitochondrial superoxide imbalance induced by some molecules, such as Rotenone could be evolutionary conservated causing behavioral, immune, and neurological alterations in animals with the primitive central nervous system. Objective: To test this hypothesis, we analyzed some behavioral, immune, and histological markers in Eisenia fetida earthworms chronically exposed to Rotenone, that causes mitochondrial impairment for 14 days. Methods: earthworms were put in an artificial soil containing 30 nM of Rotenone distributed into a plastic cup that allowed the earthworms to leave and return freely into the ground. Since these organisms prefer to be buried in the ground, the model predicted that the earthworm would necessarily have to return to the Rotenone-contaminated medium creating a stressful condition. The effect on survival behavior, in the immune and histological body wall and ventral nervous ganglia (VNG) structures were evaluated, as well gene expression related to inflammation, mitochondrial and neuromuscular changes. Results: Rotenone-induced loss of earthworm escape behavior triggered by boric acid presence; it caused immune alterations indicatives of chronic inflammatory states. Some histological changes in the body wall and VNG indicated a possible earthworm reaction aimed at protection against Rotenone. Overexpression of the nicotinic acetylcholine receptor gene (nAChRs α5) in neural tissues could also help earthworms to reduce the degenerative impact of Rotenone on dopaminergic neurons. Conclusion: The data suggest that mitochondrial dysfunction could be an evolutionarily conserved element in inducing inflammatory and behavioral changes related to exposure to chronic stress.