Combining neuropharmacology and behavior to study motion detection in flies

The optomotor following response, a behavior based on movement detection was recorded in the fruitfly Drosophila melanogaster before and after the injection of picrotoxinin, an antagonist of the inhibitory neurotransmitter GABA. The directional selectivity of this response was transiently abolished or inverted after injection. This result is in agreement with picrotoxinin-induced modifications observed in electrophysiological activity of direction-selective cells in flies (Bülthoff and Schmid 1983; Schmid and Bülthoff, in preparation). Furthermore, walking and flying flies treated with picrotoxinin followed more actively motion from back to front instead of front to back as in normal animals. Since the difference in the responses to front to back and back to front motions is proposed to be the basis of fixation behavior in flies (Reichardt 1973) our results support this notion and are inconsistent with schemes explaining fixation by alternative mechanisms.