Brain-derived Neurotrophic Factor Changes Masticatory Jaw Movements and Muscle Activities

Objectives: Recently, we indicated that the oral motor behavior of mice would be identical to that of other experimental animals, and the mouse could be an appropriate animal model to study mastication. In mice, there is mutant one lacking Brain-derived neurotrophic factor (BDNF) that trigeminal ganglion and mesencephalic trigeminal nucleus are markedly smaller than those of the wild mouse. In this study, jaw movement trajectories and muscle activities and the durations in total cycle in BDNF-lacking mice were obtained and compared with those of wild mice to examine the effects of oral sensory receptors on regulation of jaw movement pattern and masticatory muscle activity and chewing rhythm, not damaging the neurons in the trigeminal regions. Methods: Three-dimensional jaw movement trajectories and masticatory muscle activities were recorded simultaneously with foods in different texture. Results: (1) there were characteristic jaw movement patterns during food intake and during mastication, but the number of chewing stroke during mastication in BDNF-lacking mice was decreased compared to that of wild mice. (2) the pattern in a chewing cycle was divided into opening, closing and protruding phases, but each chewing pattern in BDNF-lacking mice was more irregular than that of wild mice. (3) there were significant differences in the amplitude of masseter muscle between mice (p < 0.01: t-test). The masseter muscle activities of BDNF-lacking mice were 35% and 32% smaller than those of wild mice during the chewing of hard food and soft food, respectively. (4) there were no significant differences in the cycle duration between mice. Conclusion: These results suggest the pattern generator is more susceptible to peripheral sensory inputs than the rhythm generator.