Entity

Time filter

Source Type


Thany S.H.,CNRS Receptors and Membrane Ion Channels Laboratory
Advances in Experimental Medicine and Biology | Year: 2010

Insect nicotinic acetylcholine receptors have been objects of attention since the discovery of neonicotinoid insecticides. Mutagenesis studies have revealed that, although the detailed subunit composition of insect nicotinic acetylcholine receptors subtypes eludes us, the framework provided by mutagenesis analysis makes a picture of the subunits involved in the ligand binding and channel properties. In fact, many residues that line the channel or bind to the ligand seemed to be strongly conserved in particular in the N-terminal extracellular region and the second transmembrane domain which constitutes the ion-conducting pathway supporting the flux of ions as well as their discrimination. In fact, the positions are carried by loops B and C, respectively, which contain amino acids directly contributing to the acetylcholine binding site. Mutation of these residues accounts for insect resistance to neonicotinoid insecticides such as imidacloprid or a loss of specific binding. The discovery of the same mutation at homologous residues in different insect species or its conservation raises the intriguing question of whether a single mutation is essential to generate a resistance phenotype or whether some subunit confer insensitivity to ligand. Consequently, recent finding using information from Torpedo marmorata α1 subunit and soluble Aplysia californica and Lymnae stagnalis acetylcholine binding proteins from crystallization suggest that insect nAChR subunits had contributing amino acids in the agonist site structure which participate to affinity and pharmacological properties of these receptors. These new range of data greatly facilitate the understanding of toxin-nAChR interactions and the neonicotinoid binding and selectivity. © 2010 Landes Bioscience and Springer Science+Business Media.


Thany S.H.,CNRS Receptors and Membrane Ion Channels Laboratory
Advances in Experimental Medicine and Biology | Year: 2010

The existence of several nicotinic acetylcholine receptor genes in insects suggests that many nicotinic receptor subtypes are present, but the identification and characterization of these subtypes in native neurons has been limited. Their pharmacological properties came from electrophysiological studies in which variations in the sensitivity of insect neurons were correlated with time course, current amplitudes, desensitization rates occurring in varying proportions in different cells. Thus pressure application of agonists on cultured cells induced inward currents showing that acetylcholine and nicotine were partial agonists of some cells with a lower efficacy while they were full agonists in other neurons. The variation in kinetics appeared to be due to differential expression of distinct nicotinic receptor subtypes as corroborated by the blocking activity induced by antagonists. In fact, the alpha-bungarotoxin-sensitive nicotinic receptor subtypes described as homomeric could be also heteromeric receptors. Interestingly, some receptors mediating nicotinic responses have been termed 'mixed' receptors because they were blocked by a range of nicotinic and muscarinic antagonists. Following electrophysiological studies, it has been also demonstrated that insect nicotinic receptors were modulated by Ca2+ pathways. Ca2+ permeability through insect nicotinic receptors, voltage-gated Ca2+ channels or released from intracellular stores represents an important indication of insect native nicotinic acetylcholine receptor modulation. The Ca2+ flow may trigger a variety of cytosolic Ca2+ pathways underlying many cellular processes such Calmodulin kinase, PKA and PKC. Most of the studies suggested that the effect of phosphorylation mechanism was dependent on the receptor subtype. © 2010 Landes Bioscience and Springer Science+Business Media.


Thany S.H.,CNRS Receptors and Membrane Ion Channels Laboratory
Advances in Experimental Medicine and Biology | Year: 2010

A major criteria initially used to localize cholinergic neuronal elements in nervous systems tissues that involve acetylcholine (ACh) as neurotransmitter is mainly based on immunochemical studies using choline acetyltransferase (ChAT), an enzyme which catalyzes ACh biosynthesis and the ACh degradative enzyme named acetylcholinesterase (AChE). Immunochemical studies using anti-ChAT monoclonal antibody have allowed the identification of neuronal processes and few types of cell somata that contain ChAT protein. In situ hybridization using cRNA probes to ChAT or AChE messenger RNA have brought new approaches to further identify cell bodies transcribing the ChAT or AChE genes. Combined application of all these techniques reveals a widespread expression of ChAT and AChE activities in the insect central nervous system and peripheral sensory neurons which implicates ACh as a key neurotransmitter. The discovery of the snake toxin alpha-bungatoxin has helped to identify nicotinic acetylcholine receptors (nAChRs). In fact, nicotine when applied to insect neurons, resulted in the generation of an inward current through the activation of nicotinic receptors which were blocked by alpha-bungarotoxin. Thus, insect nAChRs have been divided into two categories, sensitive and insensitive to this snake toxin. Up to now, the recent characterization and distribution pattern of insect nAChR subunits and the biochemical evidence that the insect central nervous system contains different classes of cholinergic receptors indicated that ACh is involved in several sensory pathways. © 2010 Landes Bioscience and Springer Science+Business Media.


Thany S.H.,CNRS Receptors and Membrane Ion Channels Laboratory
Advances in Experimental Medicine and Biology | Year: 2010

The use of neonicotinoid insecticides has grown considerably since their introduction in 1990s. They are used extensively for the control of agriculturally important crop pests and also in the control of cat and dog fleas. Imidacloprid exploited through an elaborated structural and substituent optimization of nithiazine was launched to market in 1990. The selectivity of neonicotinoid compounds for insect species has been attributed to their binding on nicotinic acetylcholine receptors in which the negatively charged nitro- or cyano-groups of neonicotinoid compounds interact with a cationic subsite within insect nicotinic acetylcholine receptors. The first example of a pest evolving resistance to field use of neonicotinoids was Bemisia tabaci. Resistance to neonicotinoids can arise either through nAChR subtypes expression, detoxification mechanisms and/or structural alterations of target-site proteins. Consequently, a number of derivatives and analogues of imidacloprid have been generated to date. In 1992, a new neonicotinoid using acetylcholine as the lead compound has been found. This was dinotefuran, which has a characteristic tetrahydro-3-furylmethyl group instead of the pyridine-like rings of others neonicotinoids. © 2010 Landes Bioscience and Springer Science+Business Media.


Anderson P.,Swedish University of Agricultural Sciences | Anton S.,CNRS Receptors and Membrane Ion Channels Laboratory
Plant, Cell and Environment | Year: 2014

Plant volatiles are important cues for many herbivorous insects when choosing a suitable host plant and finding a mating partner. An appropriate behavioural response to sensory cues from plants and other insects is crucial for survival and fitness. As the natural environment can show both large spatial and temporal variability, herbivores may need to show behavioural plasticity to the available cues. By using earlier experiences, insects can adapt to local variation of resources. Experience is well known to affect sensory-guided behaviour in parasitoids and social insects, but there is also increasing evidence that it influences host plant choice and the probability of finding a mating partner in herbivorous insects. In this review, we will focus upon behavioural changes in holometabolous insect herbivores during host plant choice and localization of mating partners, modulated by experience to sensory cues. The experience can be acquired during both the larval and the adult stage and can influence later responses to plant volatiles and other sensory cues not only within the developmental stage but also after metamorphosis. Furthermore, we will address the neurophysiological mechanisms underlying the experience-dependent behavioural adaptations and discuss ecological and evolutionary aspects of insect behavioural plasticity based upon experience. © 2014 John Wiley & Sons Ltd.

Discover hidden collaborations