VOLTAGE-ACTIVATED AND ODOR-MODULATED CONDUCTANCES IN OLFACTORY NEURONS OF DROSOPHILA-MELANOGASTER

Voltage-activated currents and odormodulated conductances were studied in cells in semiintact Drosophila third antennal segments (the main o lfactory organ) using patch-clamp techniques. All neurons expressed ou tward currents, and most expressed labile fast transient inward curren ts with kinetics similar to Na+ currents in other systems. Action pote ntials were detected as bipolar capacitative current transients in cel l-attached or loose patches from the soma of both odor-sensitive (97%) and insensitive neurons. A mixture of odorants from five chemical cla sses caused an increase (similar to 70%), decrease (similar to 10%), o r no effect on firing frequency in pharate adult neurons. The developm ent of chemosensitivity was examined and odor-induced changes in actio n potential firing frequency were recorded in pupal antennal neurons a s early as P8, a stage after completion of sensillar development. The character of odor-induced responses was more profound and complex late r in development; small, tonic increases in firing frequency were obse rved at pupal stages P8 through Pll(ii), while in older pupae and youn g adults similar to 25% of the increased responses were phasic-tonic. The apical dendrite was the site of odor modulation in similar to 90% and 100% of responsive adult and early pupal neurons, respectively. Wh ole-cell recordings revealed that apparent nonselective cation and chl oride conductances were modulated by a mixture of odorants in separate antennal neurons. (C) 1997 John Wiley & Sons, Inc.