Evaluation of study design variables and their impact on food-maintained operant responding in mice

Abstract

Operant conditioning paradigms are useful for studying factors involved in reward, particularly when combined with the tools of genetic manipulation in mice. Published operant studies involving mice vary widely with respect to design, and insight into the consequences of design choices on performance in mice is limited. Here, we evaluated the impact of five design variables on the performance of inbred male mice in operant tasks involving solid food pellets as reinforcing agents. We found that the use of lever-press or nose-poke during FR1 sessions did not impact the performance of C57BL/6 mice, but that the lever-press approach correlated with enhanced performance during PR testing. While FR1 session duration had a notable impact on the rate of acquisition of foodmaintained responding, performance during FR1 and PR sessions was largely unaffected. Higher order schedules of reinforcement (FR3 and FR5) led to elevated responding during both FR and PR sessions, and improved the correspondence between rewards earned and consumed. Single and group-housed mice performed indistinguishably during FR1 and PR sessions, while environmental enrichment combined with group housing accelerated the rate of acquisition of food-maintained responding while decreasing responding during PR testing. Finally, while C57BL/6 and 129/Sv mice exhibited comparable behavior during FR1 sessions, C57BL/6 mice tended to acquire foodmaintained responding faster than 129/Sv counterparts, and exhibited elevated responding during PR testing. Altogether, our findings indicate that while operant performance for food in mice is relatively insensitive to many study parameters, experimental outcomes can be shaped predictably with proper design decisions.

ROBucket: A low cost operant chamber based on the Arduino microcontroller

“…Mice required between 5 and 8 days, with an average of 6.3 days, to meet the acquisition criteria. These results are consistent with operant training on commercially sold systems, and the acquisition curves of the reinforced mice were similar to those of mice trained in commercially sold chambers (Haluk and Wickman, 2010;Sharma et al, 2012).…”

Sustained attention in mice: Expanding the translational utility of the SAT by incorporating the Michigan Controlled Access Response Port (MICARP)

“…Force requirements for pressing levers, species-specific sensorimotor repertoires and response preferences collectively appear to account for substantial strain-specific differences in the rate of acquisition of lever pressing responses by mice and high variability of performance of operant schedules of tasks using this operandum [11,21,44,55]. However, not all studies support this conclusion [28], suggesting that the utility of lever pressing depends on complex, task- and strain-related variables.…”

Progressive-ratio Responding for Palatable High-fat and High-sugar Food in Mice

“…*Acquisition Criteria: The criteria used to determine acquisition of food-maintained operant responding includes: (1) a minimum number of active responses and rewards earned; (2) a measure of discrimination between active and inactive levers, and (3) between-session performance stability. Mice exhibiting discrimination of ≥3:1 for the active versus inactive lever and obtaining ≥ 20 rewards per session over three consecutive sessions are considered to achieve acquisition criteria 10 . We have observed that the majority (~75%) of C57BL6 mice require about 7-10 days of training to achieve acquisition criteria.…”