Feeding is critical for survival and disruption in the mechanisms that govern food intake underlie disorders such as obesity and anorexia nervosa. It is important to understand both food intake and food motivation to reveal mechanisms underlying feeding disorders. Operant behavioral testing can be used to measure the motivational component to feeding, but most food intake monitoring systems do not measure operant behavior. Here, we present a new solution for monitoring both food intake and motivation in rodent home-cages: The Feeding Experimentation Device version 3 (FED3). FED3 measures food intake and operant behavior in rodent home-cages, enabling longitudinal studies of feeding behavior with minimal experimenter intervention. It has a programmable output for synchronizing behavior with optogenetic stimulation or neural recordings. Finally, FED3 design files are open-source and freely available, allowing researchers to modify FED3 to suit their needs.

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 >10x 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.

ObjectiveAd libitum high fat diet (HFD) spontaneously increases caloric intake in rodents, which correlates positively with weight gain. However, it remains unclear why rodents overeat HFD. We investigated how changing the proportion of diet that came from HFD might alter daily caloric intake in mice.MethodsMice were given 25%, 50%, or 90% of their daily caloric need from HFD, along with ad libitum access to a low-fat rodent chow diet. Food intake was measured daily to determine how these HFD supplements impacted total daily caloric intake. Follow up experiments addressed timing of HFD feeding.ResultsHFD supplements did not alter total caloric intake or body weight. In a follow up experiment, mice consumed ~50% of their daily caloric need from HFD in 30 minutes during the light cycle, a time when mice do not normally consume food.ConclusionsHFD did not disrupt regulation of total daily caloric intake, even when up to 90% of total calories came from HFD. However, HFD increased daily caloric intake when provided ad libitum, and was readily consumed by mice outside of their normal feeding cycle. Ad libitum HFD appears to induce overconsumption beyond the mechanisms that regulate daily caloric intake.

The operant conditioning chamber is a cornerstone of animal behavioral research. Operant boxes are used to assess learning and motivational behavior in animals, particularly for food and drug reinforcers. However, commercial operant chambers cost several thousands of dollars. We have constructed the Rodent Operant Bucket (ROBucket), an inexpensive and easily assembled open-source operant chamber based on the Arduino microcontroller platform, which can be used to train mice to respond for sucrose solution or other liquid reinforcers. The apparatus contains two nose pokes, a drinking well, and a solenoid-controlled liquid delivery system. ROBucket can run fixed ratio and progressive ratio training schedules, and can be programmed to run more complicated behavioral paradigms. Additional features such as motion sensing and video tracking can be added to the operant chamber through the array of widely available Arduino-compatible sensors. The design files and programming code are open source and available online for others to use.