EN
INTRODUCTION: Encephalization, i.e., the amount of brain mass related to an animal’s total body mass is increased in homeotherms comparing to ectotherms. A larger brain offers behavioral advantages, but also means energy expenditures that are an order of magnitude higher than in ectotherms. What are the benefits of larger, energetically expensive brains that allowed them to evolve? The ‘Expensive Tissue’ hypothesis links evolution of enlarged brain to increased cognitive skills that improve foraging performance. AIM(S): We aim at testing the ET hypothesis using two lines of mice bred for low and high basal metabolic rate (BMR). METHOD(S): Low (L-BMR) and high (H-BMR) lines of Swiss Webster mice were selected reaching 40% between-line difference in BMR. The weight of their internal organs, including the brain, their cognitive abilities and neural plasticity were measured. The cognitive abilities of the mice were tested in IntelliCage system which allows for assessment of learning of individual mice living in the social group. To test the brain plasticity-related differences between the lines we used a model of neural plasticity, CA3-CA1 hippocampal long-term potentiation (LTP). RESULTS: The weight of internal organs differed, with H-BMR mice organs being heavier. We found increased exploration of the environment in H-BMR mice, which also showed higher motivation to obtain the reward and faster learning of the reward’s position. In line with learning results, we found that LTP was induced at significantly higher level in H-BMR mice, suggesting higher neural plasticity in this line. CONCLUSIONS: Together, our results suggest that higher BMR is associated with more efficient exploration of the environment, higher motivation and better place learning. Increased cognitive skills, probably mediated by enhanced neuroplasticity, allow for improved foraging performance, in line with the ET hypothesis. FINANCIAL SUPPORT: Project is financed by the National Science Centre grant (NCN 2015/17/B/NZ8/02484).