Assessment of voluntary drug and alcohol intake in Drosophila melanogaster using a modified one-tube capillary feeding assay

Abstract

Background

The capillary feeding assay measures intakes of solutions containing ethanol and other drugs of abuse in the fruit fly Drosophila melanogaster. Existing single-tube and two-choice variations of the assay conflate drug intake with nutrient intake and utilize conditions that decrease lifespan of flies, suggesting these conditions might serve as a physiological stressor.

New method

The current experiments used a novel variation of a single-tube capillary feeding assay with flies maintained on standard, semi-soft food throughout the experiment, and offered a drug in a moderately preferred sucrose solution. Preference or aversion for a drug-containing solution was assessed relative to a control sucrose solution.

Results

We found concentration-dependent preferences for solutions containing ethanol or fencamfamine, aversions to solutions containing amphetamine, caffeine, muscimol, nicotine, pentobarbital, or picrotoxin, and a nominal aversion to solutions containing methamphetamine. Some aversions were found only in male flies, although low overall intake by female flies likely contributed to this apparent sex-specific effect.

Comparison with existing method(s)

The continuous availability of semi-soft food in our assay to decouple the need for nutrients from intake of the drug-containing solution. In addition, our assay uses only a single capillary tube per vial of flies, making it less resource intensive than two-choice capillary feeding assays.

Conclusions

The availability of standard food in our modified, one-tube capillary feeding assay should prove to be useful modification of the capillary feeding assay for studies of drug intake.