DEET (N, N-diethyl-m-toluamide), is known as the most widely used repellent in the world. Although, it is effective against a large group of arthropods, its exact mode of action and molecular target are not yet known precisely. By using electrophysiological (patch clamp and oil-gap), calcium imaging and biochemical techniques, we have studied the mode of action of DEET on neurosecretory cells identified as DUM neurons of the cockroach Periplaneta americana. DEET, at high concentrations, inhibits the DUM neuron acetylcholinesterase (AChE) activity. At low concentrations, it induces an increase in intracellular calcium concentration via the activation of muscarinic acetylcholine receptors (mAChRs). In addition, the synergistic interaction between DEET and propoxur, a carbamate insecticide known to inhibit AChE, has been studied. The results show that mAChRs, correspond to new identify targets for DEET and are involved in the synergistic effect on propoxur efficacy. We further demonstrate that the repellent DEET, used at low and high concentration, acts on positive and negative allosteric sites of mAChRs, respectively. The action of DEET on the positive mAChR allosteric site is responsible for the synergistic effect via an increase in intracellular calcium concentration, which potentiates the anti-AChE effect of propoxur. Finally, the use of selective pharmacological tools has allowed the identification of the intracellular signaling pathway (PLC, PI-PLC, CaMKinase II, IP3 receptors) involved in the synergistic effect of propoxur. The results presented in this thesis will contribute to the development of new strategies based on the use of combinations of different chemical insecticides to reduce the doses of treatment while increasing the efficiency.
