Effects of fluoxetine exposure on serotonin-related activity in the sheepshead minnow (Cyprinodon variegatus) using LC/MS/MS detection and quantitation

Fluoxetine (FLX) is a selective serotonin reuptake inhibitor and is among the top 100 drugs prescribed yearly in the United States and the United Kingdom. Tissue and water extraction methods were developed to detect and quantify FLX, norfluoxetine and the associated biological compounds serotonin (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA), tryptophan (TRP) and melatonin (MEL) using LC/MS/MS. Acute mortality and sublethal physiological effects of FLX were assessed using standard static renewal toxicity tests in which juvenile sheepshead minnows (Cyprinodon variegatus) were exposed to FLX. Fluoxetine did not cause significant mortality at levels near currently reported environmental concentrations. Significant changes in neurotransmitter levels were observed within the serotonergic system in juvenile sheepshead minnows exposed at concentrations approximately one order of magnitude above those currently reported in the environment. Transformation activity ratios of a product to a precursor compound (5-HT/TRP, 5-HIAA/5-HT and MEL/5-HT) also exhibited significant changes with FLX treatment. Fluoxetine exposure did not only affect 5-HT but had additional effects both upstream and downstream of 5-HT within its synthesis and metabolic pathways. These sublethal changes within the serotonergic pathway may result in behavioral changes which could, in turn, have implications for the ecological response of populations to additional environmental stressors.