The CApillary FEeder Assay Measures Food Intake in Drosophila melanogaster

The CApillary FEeder (CAFE) assay is a simple, budget-friendly, highly reliable method for investigating mechanisms underlying food intake. Used with the highly versatile genetic model organism Drosophila melanogaster, it provides a powerful means of gaining new insights into regulatory mechanisms of food intake.

For most animals, feeding is an essential behavior for securing survival, and it influences development, locomotion, health and reproduction. Ingestion of the right type and quantity of food therefore has a major influence on quality of life. Research on feeding behavior focuses on the underlying processes that ensure actual feeding and unravels the role of factors regulating internal energy homeostasis and the neuronal bases of decision-making. The model organism Drosophila melanogaster, with its great variety of genetically traceable tools for labeling and manipulating single neurons, allows mapping of neuronal networks and identification of molecular signaling cascades involved in the regulation of food intake. This report demonstrates the CApillary FEeder assay (CAFE) and shows how to measure food intake in a group of flies for time spans ranging from hours to days. This easy-to-use assay consists of glass capillaries filled with liquid food that flies can freely access and feed on. Food consumption in the assay is accurately determined using simple measurement tools. Herein we describe step-by-step the method from setup to successful execution of the CAFE assay, and provide practical examples to analyze the food intake of a group of flies under controlled conditions. The reader is guided through possible limitations of the assay, and advantages and disadvantages of the method compared to other feeding assays in D. melanogaster are evaluated.

Eating is essential; however, deregulation of food intake resulting in eating disorders such as bulimia, anorexia or the general tendency to overeat imposes costs on individuals and society^1,2,3. The goal of the present research is to uncover regulatory mechanisms of food intake and to provide a strategy for circumventing disorder formation. Numerous studies using mammalian model organisms have provided new insights of the circuitry and the role of signaling systems in eating disorders^4,5,....

1. The CAFE Assay

NOTE: The assay consists of three components: an experimental vial, a specific lid and micro- capillaries. A plastic box with cover is used to transport the prepared vials and to control the humidity more efficiently.

1. Use a Drosophila melanogaster culture plastic vial (optional 8 cm height, 3.3 cm diameter) as a tube for the assay.
2. Seal the vial with a manufactured Plexiglas lid containing an O-ring (Figures 1A, 1B). Load flies by tapping or with a blowpipe through the lid's central opening (0.9 cm diameter), which also allows for air circulation and water supply, and clo....

Flies of the w¹¹¹⁸ genotype are used to demonstrate how the assay is performed. The w¹¹¹⁸ mutants are commonly used to generate transgenic lines and to control the genetic background of transgenes marked with the white gene. Normally, for behavioral experiments, all transgenic lines are backcrossed for five generations to the same w¹¹¹⁸ stock, which is used as an experimental control. We show different experiments: a com.......

The report describes the CAFE assay in a step-by-step fashion, focusing on the technical setup and its successful performance in the laboratory. Due to its simplicity, this assay could also be used educationally as a school experiment. The examples show that the assay allows investigation of food sensing, preference and consumption in Drosophila melanogaster over short and longer time periods (hours to days). The CAFE assay has been used widely in the field to investigate subjects including food and drug consump.......

The authors have nothing to disclose.

We thank the past and present members of the Scholz lab for discussion and Helga Döring for excellent technical support. We especially thank the members of the Biocenter workshop of the University of Cologne for their support and creativity. The work is supported by SFB 1340, SysMedAlc, and DAAD-Siemens.