Decreased resistance to extinction in ob/ob mice following operant training

Inconsistent results have emerged from past studies in which operant conditioning paradigms were used to assess the hunger motivation of genetically obese mice relative to that of normal mice. Methodological considerations indicated the need to examine operant performance to a criterion, rather than performance during time-based sessions, and then to focus upon response differences in resistance to extinction. Therefore, genetically obese (ob/ob) mice and normal littermates were trained successfully to bar-press for 100 food rewards on either a CRF or a FR-10 schedule of reinforcement. Extinction behavior was then examined over 9 daily 1-hr sessions. While obese and normal mice evidenced similar patterns of learning, or response discrimination for food rewards, they evidenced different levels of hunger motivation during extinction conditions. Obese mice displayed a greater reduction in responding across extinction sessions, or less resistance to extinction, than normal mice following training on both schedules of reinforcement. These findings suggest that ob/ob mice exhibit lower levels of hunger motivation than normal littermates.