Modulation of dopaminergic neurotransmission induced by sublethal Doses of the organophosphate trichlorfon in cockroaches Graziele Daiane Stu ̈ rmer a , Thiago Carrazoni de Freitas a , Marines de Avila Heberle a , Dênis Reis de Assis b , Lúcia Vinadé a , Antônio Batista Pereira a , Jeferson Luis Franco a , Cháriston André Dal Belo a,n a CIPBiotec, Universidade Federal do Pampa, (UNIPAMPA), Campus São Gabriel, Av. Antônio Trilha, 1847, Centro, CEP 97300-000, São Gabriel, Rio Grande do Sul, Brasil b Instituto do Cérebro do Rio Grande do Sul, Pontifícia Universidade, Católica do Rio Grande do Sul, PUCRS, Porto Alegre, RS, Brasil article info Article history: Received 17 February 2014 Received in revised form 3 August 2014 Accepted 5 August 2014 Keywords: Trichlorfon Phoetalia pallida Acetylcholinesterase Neurotoxicity Dopaminergic signaling abstract Organophosphate (OP) insecticides have been used indiscriminately, based on their high dissipation rates and low residual levels in the environment. Despite the toxicity of OPs to beneficial insects is principally devoted to the acetylcholinesterase (AChE) inhibition, the physiological mechanisms under- lying this activity remain poorly understood. Here we showed the pharmacological pathways that might be involved in severe alterations in the insect locomotion and grooming behaviors following sublethal administration of the OP Trichlorfon (Tn) (0.25, 0.5 and 1 mM) in Phoetalia pallida. Tn inhibited the acetylcholinesterase activity (46 76, 38 73 and 24 76 nmol NADPH/min/mg protein, n ¼3, p o0.05), respectively. Tn (1 mM) also increased the walking maintenance of animals (46 75 s; n ¼27; p o0.05). Tn caused a high increase in the time spent for this behavior (344 718 s/30 min, 388 718 s/30 min and 228 712 s/30 min, n ¼29–30, p o0.05, respectively). The previous treatment of the animals with different cholinergic modulators showed that pirenzepine 4atropine 4oxotremorine 4d-tubocurarine 4 tropicamide 4methoctramine induced a decrease on Tn (0.5 mM)-induced grooming increase, respectively in order of potency. Metoclopramide (0.4 mM), a DA-D 2 selective inhibitor decreased the Tn-induced grooming activity (158 712 s/30 min; n ¼29; p o0.05). Nevertheless, the effect of the selective DA-D 1 receptor blocker SCH 23390 (1.85 mM) on the Tn (0.5 mM)-induced grooming increase was significative and more intense than that of metoclopramide (54 76 s/30 min; n ¼30; p o0.05). Taken together the results suggest that a cross-talking between cholinergic M1/M3 and dopaminergic D1 receptors at the insect nervous system may play a role in the OP-mediated behavioral alterations. & 2014 Elsevier Inc. All rights reserved. 1. Introduction Organophosphate insecticides (OP) derived from phosphoric or thiophosphoric acid include parathion, malathion, diazinon, fenthion, chlorpyrifos (Nishizawa 1960; Fest and Schmidt 1982; Medegela et al. 2010), and trichlorfon (Tn) among others. Tn (metrifonate or dimethyl 2,2,2-thrichloro-1-hydroxyethyl phos- phonate) inhibits acetylcholinesterase (AChE) due to its ability to phosphorylate its serine hydrolase at its esterasic active site. AChE inhibition leads to accumulation of acetylcholine at the cholinergic junction from nerve tissue and effector organs, producing acute effects at the muscarinic and nicotinic receptors and at the central nervous system (CNS) (Torres-Altoro et al. 2011; Cummings and Ringman 1999). Tn was first registered in the United States in 1955, and nowadays is a worldwide diffused systemic insecticide with a variety of domestic and agricultural applications (EPA 2006). Li and colleagues (2011) (Li et al., 2011) have shown that the dissipation rates of Tn on soil and cabbage are about 90% in five days, suggesting that Tn is safe when applied at the recom- mended dosage. Although the dissipation and degradation rates of OP are high, the potential effect of residual amounts of these insecticides in the surrounding environment is still a matter of concern. In this way, even if their concentrations are low in the environment (Gupta et al., 2012), the reminiscent activity of these insecticides are amenable to induce long-term behavioral alterations in insects (de Castro et al., 2013; He et al., 2013, Neuman-Lee et al., 2013). During the last two decades, the effects of OP on beneficial arthropods have been the subject of an increasing number of Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ecoenv Ecotoxicology and Environmental Safety http://dx.doi.org/10.1016/j.ecoenv.2014.08.006 0147-6513/& 2014 Elsevier Inc. All rights reserved. n Correponding author at: Federal University of Pampa (UNIPAMPA) Av. Antônio Trilha, 1847 – Centro, CEP 97300-000, São Gabriel-RS, Brazil. Tel./Fax: þ55 55 3232-6075. E-mail addresses: charistonbelo@unipampa.edu.br, charistondb@gmail.com (C. André Dal Belo). Ecotoxicology and Environmental Safety 109 (2014) 56–62