Atividade entomotóxica do veneno do sapo Rhinella icterica (Spix, 1824) em baratas da espécie Nauphoeta cinerea

Abstract

Animal poisons are important sources of structurally diverse toxins with a high degree of selectivity. The Rhinella icterica toad produces, through specialized glands, a poisonous secretion rich in compounds of different chemical classes, which present a series of pharmacological activities with biotechnological potential. In this sense the toxic secretion of R. icterica (RITS) was tested against its entomotoxic activity in cockroaches of the Nauphoeta cinerea species. Initially, locomotor activity protocols were established, in which RITS induced alterations in the exploratory behavior of the animals, characterized by a significant reduction in the total distance traveled (38 ± 14%) and by a 90 ± 6% increase in the number of episodes of immobility (n = 33, p <0.05, respectively). RITS (4, 8 and 16μg / 200μl) also induced cardiotoxicity demonstrated by the reduction of up to 40% (n = 4, p <0.05) of cockroaches heart rate, irreversibly, in 30 min of records. In neuromuscular preparation in vivo, RITS (20, 50 and 100 μg / g) produced time-dependent inhibition of the contractile response for all doses tested, achieving total blockade at the of 20 μg / g dose (n = 6, p <0.05 , respectively). In addition, RITS 10μg / g, altered the leg grooming behavior of the animals, inducing increase of 128 ± 10%, (n = 29, p <0.05). When RITS was assayed in animals previously treated with phentolamine (0.1 μg / g), there was a 90% reduction in the effect of venom on leg grooming, indicating that the neurotoxic activity of the compound may be related to octopaminergic pathways. The electrophysiological records of spontaneous compound sensory potentials (SNCAP) in the legs of cockroaches demonstrated that treatment with RITS 20μg / g significantly increased the number of potentials as well as the time of onset and duration of these events (n = 6 , p <0.05). In conclusion the tests performed in this work demonstrated that RITS induces entomotoxic activity in Nauphoeta cinerea, characterized by central and peripheral nervous system modulation. The mechanism of toxicity seems to be related to a direct activity of the toxins present in the poisonous secretion on the octopaminergic pathways of the insects. Future trials of biochemical and pharmacological characterization may help identify the toxic compounds present in the secretion, as well as contribute to the elucidation of biological interactions, reinforcing the biotechnological potential of this natural compound.