title: Liquid diet induces memory impairment accompanied by a decreased number of hippocampal neurons in mice.
abstract: It is suggested that masticatory dysfunction affects the central nervous system; however, the underlying mechanism remains unknown. Brain-derived neurotrophic factor (BDNF) and its receptor, TrkB, are known to play important roles in memory and learning. In this study, we examined the effects of mastication on memory, the expression levels of BDNF and TrkB, and the number of neurons in the hippocampus of mice. Male C57 BL/6J mice (3 weeks old) were randomly divided into the control group (N = 7) fed chow pellets and the experimental group (N = 7) fed a liquid diet, which reduces mastication during eating. At 14 weeks of age, we performed a passive avoidance test and found that memory and learning ability were impaired in the experimental group compared with the control group. After the behavioral experiment, brains were harvested and analyzed morphologically and biochemically. In the hippocampus of the experimental group, the expression levels of BDNF were significantly higher, whereas those of TrkB were lower than those of the control group. In the cerebral cortex, these levels remained unchanged between the two groups. The ratio of phospho-p44/42 ERK/pan ERK, a downstream molecule of BDNF/TrkB signaling, in the experimental group was significantly lower than that of the control group in the cortex and hippocampus. The number of pyramidal neurons in the hippocampus was lower in the experimental group than in the control group. These findings suggest that reduced mastication induced by a liquid diet in early childhood may impair memory and learning ability, accompanied by neuronal loss in the hippocampus.
authors.affiliation: Department of Biochemistry, Graduate School of Medical Sciences, Nagoya City University, Nagoya, Japan; Department of Orthodontic Science, Oral Health Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Hidemasa
authors.initials: H
authors.lastname: Okihara
authors.forename: Jin-Ichi
authors.initials: J
authors.lastname: Ito
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kokai
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Ishida
authors.forename: Maya
authors.initials: M
authors.lastname: Hiranuma
authors.forename: Chiho
authors.initials: C
authors.lastname: Kato
authors.forename: Tadachika
authors.initials: T
authors.lastname: Yabushita
authors.forename: Kazuto
authors.initials: K
authors.lastname: Ishida
authors.forename: Takashi
authors.initials: T
authors.lastname: Ono
authors.forename: Makoto
authors.initials: M
authors.lastname: Michikawa
mesh_terms: D000818:Animals; D001362:Avoidance Learning / Q000502:physiology; D001522:Behavior, Animal / Q000502:physiology; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism; D002452:Cell Count; D004032:Diet; D006624:Hippocampus / Q000166:cytology* / Q000378:metabolism; D008297:Male; D008409:Mastication / Q000502:physiology*; D008569:Memory Disorders / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000166:cytology* / Q000378:metabolism; D020813:Receptor, trkB / Q000378:metabolism
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D020813:Receptor, trkB
keywords: hippocampal neuron; mastication; memory impairment; soft diet