Effects of the insecticide Fipronil on the short-term regulation of the cardiorespiratory function in neotropical fish Hoplias malabaricus, the Traíra

Abstract

Fipronil is an insecticide extensively used in rice and sugar cane monocultures in Brazil. This compound is a chloride channel antagonist regulated by gamma-aminobutyric acid (GABA) or glutamic acid (GLU), which causes death of arthropods by impediment neuronal repolarization associated with blockade of the influx of chloride into cells. Although organisms of subphylum Vertebrata do not have chloride channels regulated by glutamic acid, these animals have chloride channels regulated by GABA, and consequently are also susceptible to the effects of Fipronil - specifically because of chloride channels regulated by GABA-A receptors. These GABA-A receptors have been widely found in central and peripheral neural sites of vertebrates in association with baroreflex and chemoreflex control of cardiorespiratory function, mechanisms related to the efficiency in oxygen extraction and transport, and which are essential for sustainable production of the energy required to perform activities related to the adaptive value of animals. Thus, considering that: (1) Fipronil is frequently present in Brazilian water bodies; (2) the neural pathways involved in cardiovascular and respiratory control are highly conserved in the subphylum Vertebrata; and (3) recent studies have shown a striking influence of GABA-A receptors on basal cardiorespiratory variables and oxygen dynamics in ectothermic vertebrates, the present project aims to test the hypothesis that the insecticide Fipronil promotes important dysfunctions in the short-term regulatory mechanisms of cardiorespiratory function in a neotropical teleost (Hoplias malabaricus) frequently exposed to this pesticide - specifically reducing the efficiency of the baroreflex and chemoreflex, changing the pattern of cardiac neural control and impairing the establishment of cardiorespiratory interactions. (AU)