A Novel Injection Technique for the Measurement of Drug-Related Behaviors in Unanesthetized Fruit Flies.

BACKGROUND:Behavioral pharmacological studies in rats and mice often measure behavioral responses to ethanol or other drugs administered by injection, such that the timing of the injection provides a convenient point of reference to index the effects of the drug. Although a variety of drug administration protocols have been developed for use with the fruit fly Drosophila melanogaster, currently available techniques do not allow for a comparable bolus administration of drugs to awake, behaving flies. NEW METHOD:We developed a novel apparatus that temporarily restrains and orients unanesthetized fruit flies for an intra abdominal injection. Using this apparatus, we injected male and female flies with a constant 200 nL volume of ethanol at varying concentrations (0-50% v/v), then measured acute and protracted behavioral changes as well as survivability following the injections. RESULTS:Ethanol produced an acute biphasic effect on locomotor activity and dose-dependent increase in immobility as measured by a loss-of-righting response assay, with no significant differences by sex. A protracted, sex-dependent effect of ethanol injection was also found on the rate of locomotion measured before exposure to ethanol vapor, with male flies showing increased locomotion when measured 28 h after injection. COMPARISON WITH EXISTING METHODS:Ethanol-related behaviors following injections resemble those produced by vapor exposure. However, poor survivability after the injection will likely limit the procedure to studies of acute drug responses. CONCLUSION:Our results suggest that this injection procedure might prove useful for characterizing ethanol and drug responses in fruit flies.