Full Length Article Subchronic exposure to sublethal dose of imidacloprid changes electrophysiological properties and expression pattern of nicotinic acetylcholine receptor subtypes in insect neurosecretory cells Yassine Benzidane a , Delphine Goven a , Aly Ahmed Abd-Ella a,b , Caroline Deshayes a , Bruno Lapied a , Valérie Raymond a, * a Laboratoire Signalisation Fonctionnelle des Canaux Ioniques et des Récepteurs (SiFCIR), UPRES EA 2647, USC INRA 1330, SFR QUASAV 4207, Université Bretagne Loire, Univ. Angers, UFR Sciences, Angers Cedex, France b Plant Protection Department, Faculty of Agriculture, Assiut University, 71526 Assiut, Egypt A R T I C L E I N F O Article history: Received 10 February 2017 Received in revised form 21 July 2017 Accepted 5 August 2017 Available online 12 August 2017 Keywords: Insect Nicotinic acetylcholine receptors Insecticides Subchronic exposure Sublethal dose A B S T R A C T Neonicotinoids are the most important class of insecticides used in agriculture over the last decade. They act as selective agonists of insect nicotinic acetylcholine receptors (nAChRs). The emergence of insect resistance to these insecticides is one of the major problems, which limit the use of neonicotinoids. The aim of our study is to better understand physiological changes appearing after subchronic exposure to sublethal doses of insecticide using complementary approaches that include toxicology, electrophysiol- ogy, molecular biology and calcium imaging. We used cockroach neurosecretory cells identified as dorsal unpaired median (DUM) neurons, known to express two a-bungarotoxin-insensitive (a-bgt-insensitive) nAChR subtypes, nAChR1 and nAChR2, which differ in their sensitivity to imidacloprid. Although nAChR1 is sensitive to imidacloprid, nAChR2 is insensitive to this insecticide. In this study, we demonstrate that subchronic exposure to sublethal dose of imidacloprid differentially changes physiological and molecular properties of nAChR1 and nAChR2. Our findings reported that this treatment decreased the sensitivity of nAChR1 to imidacloprid, reduced current density flowing through this nAChR subtype but did not affect its subunit composition (a3, a8 and b1). Subchronic exposure to sublethal dose of imidacloprid also affected nAChR2 functions. However, these effects were different from those reported on nAChR1. We observed changes in nAChR2 conformational state, which could be related to modification of the subunit composition (a1, a2 and b1). Finally, the subchronic exposure affecting both nAChR1 and nAChR2 seemed to be linked to the elevation of the steady-state resting intracellular calcium level. In conclusion, under subchronic exposure to sublethal dose of imidacloprid, cockroaches are capable of triggering adaptive mechanisms by reducing the participation of imidacloprid-sensitive nAChR1 and by optimizing functional properties of nAChR2, which is insensitive to this insecticide. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Neonicotinoids are the most important class of insecticides used in agriculture over the last decade and are effective against some crop pests such as aphids, thrips and whiteflies. Imidacloprid was the first product of this class of insecticides to be commercialized in 1991 and it was used in foliar application and seed treatments (Tomizawa and Casida, 2003). Neonicotinoids act as selective agonists of insect nicotinic acetylcholine receptors (nAChRs) (Tomizawa and Casida, 2005), which belong to the “cys- loop” superfamily of ligand-gated ion channels (Ffrench-Constant et al., 2016). These receptors are composed of five subunits (Jones et al., 2007), each subunit possesses four transmembrane domains (M1-M4), an extracellular amino-terminal domain involved in agonist binding and a large cytoplasmic loop between M3 and M4 containing several phosphorylation sites (Dupuis et al., 2012). Subunits were classified into two groups a and non a or b, depending on the presence or not of two adjacent cysteine residues in the extracellular domain, which play an important role for acetylcholine binding (Jones et al., 2007). In insects, several nAChR subunits have been cloned and the sequencing of the entire insect genome has revealed the existence of approximately ten different * Corresponding author. E-mail address: valerie.raymond@univ-angers.fr (V. Raymond). http://dx.doi.org/10.1016/j.neuro.2017.08.001 0161-813X/© 2017 Elsevier B.V. All rights reserved. NeuroToxicology 62 (2017) 239–247 Contents lists available at ScienceDirect NeuroToxicology