Drosophila nervous system muscarinic acetylcholine receptor: transient functional expression and localization by immunocytochemistry.

The pharmacological properties of a cloned Drosophila muscarinic acetylcholine receptor (mAChR) were investigated using two independent transient expression systems. The binding characteristics of the expressed receptor were determined using transfected COS-7 cells, whereas the mAChR functional properties were analyzed using nuclearly injected Xenopus oocytes. Competition displacement studies with transfected COS-7 cell membranes showed that N-[3H]methylscopolamine binding was displaced most effectively by atropine, followed by 4-diphenylacetoxy-N-methylpiperidine methiodide, pirenzepine, and AFDX-116. This same order of effectiveness (4-diphenylacetoxy-N-methylpiperidine methiodide > pirenzepine > AFDX-116) was observed in oocytes expressing Dm1 when carbamylcholine-induced currents were inhibited by the same antagonists. Thus, the expressed Drosophila mAChR (Dm1) exhibits a pharmacology that broadly resembles that of the vertebrate M1 and M3 mAChR subtypes. To determine the anatomical localization of the Drosophila mAChR, polyclonal antiserum was raised against a peptide corresponding to the predicted carboxyl-terminal domain of the receptor. Immunocytochemistry on fly sections demonstrated that the mAChR gene product was found in the nervous system and was not seen in skeletal muscle. The most intense staining was localized to the glomeruli of the antennal lobes, an area of the insect brain where first-order synaptic processing of olfactory information occurs.