Feeding Experimentation Device (FED): A flexible open-source device for measuring feeding behavior

Abstract

Background: Measuring food intake in rodents is a conceptually simple yet labor-intensive and temporally-imprecise task. Most commonly, food is weighed manually, with an interval of hours or days between measurements. Commercial feeding monitors are excellent, but are costly and require specialized caging and equipment.

New method: We have developed the Feeding Experimentation Device (FED): a low-cost, open-source, home cage-compatible feeding system. FED utilizes an Arduino microcontroller and open-source software and hardware. FED dispenses a single food pellet into a food well where it is monitored by an infrared beam. When the mouse removes the pellet, FED logs the timestamp to a secure digital (SD) card and dispenses a new pellet into the well. Post-hoc analyses of pellet retrieval timestamps reveal high-resolution details about feeding behavior.

Results: FED is capable of accurately measuring food intake, identifying discrete trends during light and dark-cycle feeding. Additionally, we show the utility of FED for measuring increases in feeding resulting from optogenetic stimulation of agouti-related peptide neurons in the arcuate nucleus of the hypothalamus.

Comparison to existing methods: With a cost of ∼$350 per device, FED is >10× cheaper than commercially available feeding systems. FED is also self-contained, battery powered, and designed to be placed in standard colony rack cages, allowing for monitoring of true home cage feeding behavior. Moreover, FED is highly adaptable and can be synchronized with emerging techniques in neuroscience, such as optogenetics, as we demonstrate here.

Conclusions: FED allows for accurate, precise monitoring of feeding behavior in a home cage setting.

Keywords: Arduino; Feeding behavior; Food intake; Open-source.

Fig. 1

(A) 3D printed housing and hardware. Exploded view of hardware assembly and main components used to hold pellets, individually dispense pellets, and mount the stepper motor. (B) FED electronics. Six main electronic components are used to operate FED: an Arduino microcontroller, data logging shield, Adafruit motor shield, stepper motor, photo interrupter board, and Li-ion battery pack. (C) Electronic configuration. Circuitry wiring of each component to the Arduino microcontroller, highlighting the stacking shields of the Arduino that minimizes the number of additional wires and connections needed.

Fig. 2

(A) Representative image of FED in a home cage. Mice were housed in home cages equipped with a single FED system per cage. (B) Daily food intake measured via FED vs manual methods. Daily food intake measurements from FED are comparable to those obtained through manual weighing of chow (p > 0.05). (C) Circadian food intake measured via FED. Food intake is significantly greater during the dark cycle versus the light cycle (D) Pellet retrievals occur primarily, but not exclusively, during the dark cycle. Top panel: individual spikes indicate single pellet retrieval events by individual mice (illustrated by different colors). Bottom panel: average pellet retrieval over 72 hr in 30 min bins. Shading depicts the dark cycle (lights on at 06:00). n = 8/group. ***p < 0.001.

Fig. 3

(A) Representative dark cycle food intake measured via FED. Individual spikes indicate single pellet retrievals, and horizontal bars indicate meals defined as consumption of ≥0.3 g separated by other feeding bouts by ≥15 min; dark cycle: 18:00–06:00). (B) Representative light cycle food intake measured via FED. Individual spikes indicate single pellet retrievals, and horizontal bars indicate meals (light cycle: 06:00–18:00). (C-H) Individual feeding parameters were analyzed for circadian effects. Meal duration, meal size, eating rate, and the proportion of pellets consumed as part of a meal were significantly greater during the dark cycle compared to the light cycle, while no difference was found in number of meals or satiety ratio. n = 8. *p < 0.05 **p < 0.01.

Fig. 4

(A) Schematic illustrating viral construct and fiber placement in the ARC. To artificially evoke feeding, AgRP-IRES-Cre mice received infusion of AAV10-ChR2-tdTomato and implantation of an optic fiber above the ARC (shown in red). (B) Representative confocal micrograph illustrating selective ChR2-tdTomato infection of AgRP neurons. Images taken at 20x; scale bar = 100 μm. (C) Optogenetic stimulation of AgRP^ARC neurons induces pellet retrieval. Individual spikes indicate single pellet retrieval events by individual mice (illustrated by different colors). Photostimulation is indicated by blue shading. (D) Average pellets retrieved during each phase of the experiment. Stimulation of AgRP^ARC neurons significantly increased pellet retrieval during the Stim-1 period compared to the No-stim period. n = 3. *p < 0.05.