NEURONAL NICOTINIC RECEPTORS IN THE LOCUST LOCUSTA-MIGRATORIA - CLONING AND EXPRESSION

We have identified five cDNA clones that encode nicotinic acetylcholin e receptor (nAChR) subunits expressed in the nervous system of the loc ust Locusta migratoria. Four of the subunits are ligand-binding alpha subunits, and the other is a structural beta subunit. The existence of at least one more nAChR gene, probably encoding a beta subunit, is in dicated. Based on Northern analysis and in situ hybridization, the fiv e subunit genes are expressed. loc alpha 1, loc alpha 3, and loc beta 1 are the most abundant subunits and are expressed in similar areas of the head ganglia and retina of the adult locust. Because Loc alpha 3 binds alpha-bungarotoxin with high affinity, it may form a homomeric n AChR subtype such as the mammalian alpha 7 nAChR Loc alpha 1 and Loc b eta 1 may then form the predominant heteromeric nAChR in the locust br ain. loc alpha 4 is mainly expressed in optic lobe ganglionic cells an d loc alpha 2 in peripherally located somata of mushroom body neurons. loc alpha 3 mRNA was additionally detected in cells interspersed in t he somatogastric epithelium of the locust embryo, suggesting that this isoform may also be involved in functions other than neuronal excitab ility, Transcription of all nAChR subunit genes begins approximately 3 days before hatching and continues throughout adult life. Electrophys iological recordings from head ganglionic neurons also indicate the ex istence of more than one functionally distinct nAChR subtype, Our resu lts suggest the existence of several nAChR subtypes, at least some of them heteromeric, in this insect species.