Altered motor function in zebrafish larvae exposed to sulfonamide and fluoroquinolone antibiotics: behavioral, cellular, and molecular responses

Abstract

The occurrence of antibiotics in freshwater has been documented worldwide, however, data on the neurotoxicity of these substances in the context of animal behavior are lacking. In this research proposal, the mechanisms associated with the alteration of the motor function of zebrafish larvae exposed to widely used antibiotics (sulfonamides and fluoroquinolones) will be analyzed, combining behavioral responses with those at the cellular and molecular levels. Ten candidate antibiotics studied in Brazil were selected, five from the sulfonamide class: sulfamethoxazole (SMX), sulfadiazine (SDZ), sulfamethazine (SMZ), sulfamerazine (SMR), sulfadimethoxine (SDM); and five from the fluoroquinolone class: ciprofloxacin (CIP), norfloxacin (NOR), pefloxacin (PEF), ofloxacin (OFL), and enrofloxacin (ENR). Zebrafish larvae (7 dpf) will be exposed to independent mixtures of sulfonamides and fluoroquinolones for 24 hours, in three groups of environmentally relevant concentrations 0.1; 1 and 10 µg/L, for each class of antibiotics. Behavioral responses will be analyzed: baseline locomotor activity, startle response, habituation to repetitive acoustic stimulation, and visuomotor response. On the other hand, cellular alterations in the sensory system will be analyzed by micrographs of neurons and neuromasts of zebrafish. In addition, changes in the expression of genes involved in the locomotor functions of the fish (appb, cdh6 and ralgapa1), and in biochemical markers of oxidative stress (SOD, GSH, LPO and ROS) will be evaluated. This multilevel analysis will help to understand the behavioral damage caused by mixtures of antibiotics in a key vertebrate species of toxicological studies. (AU)