Novel natural ligands for Drosophila olfactory receptor neurones.

Due to its well-defined genome, the fruitfly Drosophila melanogaster has become a very important model organism in olfactory research. Despite all the research invested, few natural odour ligands have been identified. By using a combined gas chromatographic-single receptor neurone recording technique (GC-SC), we set out to identify active odour molecules in head space-collected volatiles from preferred food sources, i.e. different overripe or rotting fruit. In total, we performed 101 GC-SC experiments on 85 contacted sensilla. Using GC-mass spectrometry, we identified 24 active compounds. Synthetic samples of these compounds were used to establish dose-response curves for several of the receptor neurone types encountered. The response patterns of individual neurones were repeatable, and neurones were found to reside in stereotyped pairs. In total, we identified eight distinct sensillum types based on response profiles of 12 olfactory receptor neurone types. In most recordings, a single GC peak would produce a strong response, whereas a few other, often chemically related, compounds would produce weaker responses. The GC-SC recordings revealed that the olfactory receptor neurones investigated were often selective and could be divided into distinct functional types with discrete characteristics. Dose-response investigations revealed very low response thresholds to the tested compounds. Six of the novel ligands were also tested for their behavioural effect in a T-maze set up. Of these, five elicited attraction and one elicited repulsion.