Investigação dos mecanismos associados à entomotoxicidade da urease de Canavalia Ensiformis (JBU) sobre o sistema nervoso de Nauphoeta cinerea: envolvimento dos sistemas monoaminérgicos

Abstract

The entomotoxicity of JBU and its derived peptides turned to the object of study in the last decades, due to a wide interaction of these compounds with different insect species and their potential natural insecticidal activity. Despite the diversity of studies aimed to understand the entomotoxic effects of JBU, the mechanism of action remains elusive. In this work, we investigated the entomotoxic effects of JBU in cockroaches of Nauphoeta cinerea species, on monoaminergic neurolocomotor pathways. Selective pharmacological instruments of monoaminergic receptors were used in in vivo and ex vivo assays. Thus, an analysis of N. cinerea neurolocomotor behavior demonstrates that JBU (1.5 and 3μg/g) induces a significant decrease in the distance traveled while increasing the effects of immobility and stopping times. In these trials, pretreatment of animals with phentolamine, SCH23390 (dopaminergic antagonist) or reserpine (monoaminergic antagonist), alter the standard response of JBU. In metathoracic abductor coxal nerve-muscle preparations (NMCAM), JBU (1.5 μg/g) induces progressive neuromuscular block, in 120min. In these sets of protocols, pretreatment of animals with phentolamine, SCH23390 or reserpine inhibited JBU-induced neuromuscular blockade. In the assays for recording Spontaneous Neural Compound Action Potentials (PACNE) on Nauphoeta cinerea leg, in the presence of JBU (1.5 μg / g), there was a significant difference in the number of potentials, in 60min recordings. In these assays, pretreatment with phentolamine, SCH23390 or reserpine also prevented JBU response. In all of the above assays, treatment of the animals with mianserin (a serotonergic antagonist), was ineffective in altering JBU neurophysiological responses. In conclusion, in our experimental conditions, the JBU entomotoxic response in Nauphoeta cinerea has been demonstrated to involve primarily octopaminergic and dopaminergic pathways, but not the serotonergic neurotransmission. Future in situ electrophysiological and molecular cell biology assays may identify receptors that might affect the entomotoxic JBU response in Nauphoeta cinerea.