Neuronal Nicotinic Receptors in the Locust Locusta migratoria

Abstract

We have identified five cDNA clones that encode nicotinic acetylcholine receptor (nAChR) subunits expressed in the nervous system of the locust Locusta migratoria. Four of the subunits are ligand-binding ␣ subunits, and the other is a structural ␤ subunit. The existence of at least one more nAChR gene, probably encoding a ␤ subunit, is indicated.Based on Northern analysis and in situ hybridization, the five subunit genes are expressed. loc␣1, loc␣3, and loc␤1 are the most abundant subunits and are expressed in similar areas of the head ganglia and retina of the adult locust. Because Loc␣3 binds ␣-bungarotoxin with high affinity, it may form a homomeric nAChR subtype such as the mammalian ␣7 nAChR. Loc␣1 and Loc␤1 may then form the predominant heteromeric nAChR in the locust brain. loc␣4 is mainly expressed in optic lobe ganglionic cells and loc␣2 in peripherally located somata of mushroom body neurons. loc␣3 mRNA was additionally detected in cells interspersed in the somatogastric epithelium of the locust embryo, suggesting that this isoform may also be involved in functions other than neuronal excitability. Transcription of all nAChR subunit genes begins approximately 3 days before hatching and continues throughout adult life.Electrophysiological recordings from head ganglionic neurons also indicate the existence of more than one functionally distinct nAChR subtype. Our results suggest the existence of several nAChR subtypes, at least some of them heteromeric, in this insect species.In insects, neuromuscular transmission is mediated by glutamate, whereas acetylcholine is the principal neurotransmitter in the nervous system (1). A large body of evidence suggests the existence of both muscarinic and nicotinic acetylcholine (nAChR) 1 receptors in the insect brain, with nAChR-coding RNAs having been identified in several species, including the fruit fly Drosophila (2), the locust Schistocerca (3), the tobacco hornworm Manduca (4), and the peach-tomato aphid Myzus (5). Considerable pharmacological diversity of nicotinic receptors is indicated by the existence of ␣BTX-sensitive and -insensitive receptors (6, 7) and by the rather wide variation of responses to nicotinic and non-nicotinic drugs of insect neurons and membrane preparations (8, 9). In particular, the nAChR of Locusta migratoria was suggested to have mixed nicotinic and muscarinic pharmacology (10), which could correlate with the greater evolutionary age of orthoperians as compared with dipterians.Vertebrate neuronal nicotinic receptors are quite diverse (11), with to date eight ␣ subunits and three ␤ subunits cloned in the rat. Of these, the ␣7, ␣8, and ␣9 subunits have the unique ability to form functional homomeric receptors (12)(13)(14). Various combinations of the other ␣ and ␤ subunits also give rise to functional receptors, as is exemplified by combinations of ␣4 and ␤2 subunits and of ␣3 and ␤4 subunits expressed in hippocampal neurons (15). The stoichiometries of heteromeric neuronal nAChRs are not yet established.The homo-oligomeric receptors app...

A nicotinic acetylcholine receptor mutation conferring target-site resistance to imidacloprid inNilaparvata lugens(brown planthopper)

“…22 and 26, initial characterization of recombinant nAChRs containing insect and vertebrate (rat) nAChR subunits was conducted with [ 3 H]epibatidine. As has been found with nAChR subunits cloned from other insect species (22,26,36), no specific radioligand binding could be detected with any combination of N. lugens nAChR subunits. Despite difficulties in heterologous expression of insect nAChR subunits, a strategy that has proved successful with several insect species is to coexpress insect nAChR ␣ subunits with a vertebrate non-␣ subunit such as rat ␤2 (26,27,37 n ϭ 3; Fig.…”

Critical roles of mecamylamine-sensitive mushroom body neurons in insect olfactory learning

“…In insects, two types of nicotinic ACh receptors (nAChRs) are pharmacologically identified: one type is antagonized by α-bungarotoxin and the other type is not (Goldberg, Grünewald, Rosenboom, & Menzel, 1999;Hermsen, Stetzer, Thees, Heiermann, Schrattenholz, Ebbinghaus, Kretschmer, Methfessel, Reinhardt, & Maelicke, 1998;Jones, Raymond-Delpech, Thany, Gauthier, & Sattelle, 2006;Thany, Lenaers, Raymond-Delpech, Sattelle, & Lapied, 2007). In studies using isolated dorsal unpaired median neurons of the cockroach, α-bungarotoxin-insensitive nAChRs have been further divided into mecamylamine (MEC)-sensitive and d-tubocurarine-sensitive types, and the biophysical and pharmacological properties of both types have been characterized (Courjaret, Grolleau, & Lapied, 2003;Courjaret & Lapied, 4 2001; Thany, Courjaret, & Lapied, 2008).…”

Minor structural changes in nicotinoid insecticides confer differential subtype selectivity for mammalian nicotinic acetylcholine receptors

“…Although several candidate genes encoding the a and non-a subunits are identi®ed from fruit¯ies (Drosophila melanogaster) and migratory locusts (Locusta migratoria), their functional coexpression has not been successful in any combination, implying the involvement of unidenti®ed subunit(s) in assembling the native insect receptors (Gundel®nger & Hess, 1992;Tomizawa et al, 1996;Tomizawa & Casida, 1997;Hermsen et al, 1998). Interestingly, functional ion channel properties are clearly observed when either of two Drosophila a type subunits is coexpressed with chick b 2 subunit and the two reconstituted Drosophila a/ chick b receptors display dierent sensitivities to a-BGT (Bertrand et al, 1994).…”