Reduced mastication stimulates impairment of spatial memory and degeneration of hippocampal neurons in aged SAMP8 mice

Onozuka, Minoru; Watanabe, Kazuko; Mirbod, Seyed Mohammad; Ozono, Satoru; Nishiyama, Kozaburo; Karasawa, Nobuyuki; Nagatsu, Ikuko

doi:10.1016/s0006-8993(99)01255-x

Cited by 157 publications

(182 citation statements)

References 23 publications

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“…Many investigators (3, 9, 10, 12) also reported the relationship between aging and decrease of hippocampal neurons. In aged or soft-diet feeding SAMP8 mice with molar extraction, the neuron density in the hippocampus was significantly reduced compared with the controls (14,21). In this study, significant reduction of the total number of pyramidal cells in the hippocampal CA1 and CA3 regions was similarly ron loss was clearly observed in the group D as compared with the remaining groups (Figs.…”

Section: Methodssupporting

confidence: 57%

“…To examine memory/learning ability, the animals were subjected to the Morris water maze (11). In this study, various conditions for the water maze experiment were defined based on a previous report of Onozuka et al (14) as follows. The maze is consisted of a circular plastic tank (60 cm diameter), of which the inner wall is painted white.…”

Section: Methodsmentioning

confidence: 99%

“…Yamamoto and Hirayama showed that the SAMR1 and SAMP8 mice fed on a solid diet were superior in an eight-arm radial maze to the powder-diet group (21). It was also reported that the aged SAMP8 mice, after the molar extraction, showed a decrease in both learning ability and neuron density in the hippocampal CA1 region compared with the controls (14). Furthermore, it is suggested that afferent sensory input is highly dependent on masticatory function or hardness of the diet (13).…”

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confidence: 97%

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Influences of reduced masticatory sensory input from soft-diet feeding upon spatial memory/learning ability in mice

et al. 2007

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It has been reported that reduction of masticatory afferent stimulation might influence learning and memory function. In order to clarify the influences of reduced masticatory sensory input on spatial memory/learning ability and neuropathological changes, we conducted the Morris water maze experiment and investigated the number of hippocampal neurons in association with the differences in masticatory afferent stimuli from hard-and soft-diet feeding in mice. The water maze experiment showed no significant difference in learning ability between 180-day-old solid-and powderdiet groups. Meanwhile, the ability was significantly reduced in the 360-day-old powder-diet group as compared with the age-matched solid-diet group. The total number of pyramidal cells in the hippocampal CA1 and CA3 regions was significantly smaller in 360-day-old powder-diet group than in the remaining groups. These results demonstrate that reduction of masticatory afferent stimuli due to long-term soft-diet feeding may induce neuron loss in the hippocampus and reduced memory/learning ability.Alzheimer's disease (AD) is a progressive neurodegenerative disorder, which was first reported by Alzheimer in 1907 (1, 18). It is, in general, divided into early and late-onset types, but both have similar clinical and pathological features. It has long been suggested that there is a certain relationship between loss of teeth and dementia. Kondo et al. (6) reported that tooth loss was one of the risk factors of AD. Shigetomi et al. (17) reported that the risk of AD onset increased significantly in a group with lessnumber teeth than in the age-matched control with more-number teeth. Animal experiments revealed that tooth loss or long-term soft-diet feeding caused a decrease of learning and memory ability. Yamamoto and Hirayama showed that the SAMR1 and SAMP8 mice fed on a solid diet were superior in an eight-arm radial maze to the powder-diet group (21). It was also reported that the aged SAMP8 mice, after the molar extraction, showed a decrease in both learning ability and neuron density in the hippocampal CA1 region compared with the controls (14). Furthermore, it is suggested that afferent sensory input is highly dependent on masticatory function or hardness of the diet (13). Ishizuka (5) demonstrated that the action potential of the masseter muscle in rats was significantly lower in the powder-diet group than in the solid-diet group.It is reasonably assumed from these findings that tooth loss and the relevant reduction of masticatory afferent stimuli may influence the structure and function of the central nervous system (CNS). However, little information is available for the relation-

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Section: Methodssupporting

confidence: 57%

Section: Methodsmentioning

confidence: 99%

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Influences of reduced masticatory sensory input from soft-diet feeding upon spatial memory/learning ability in mice

et al. 2007

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“…The Morris water maze test is a sensitive behavioral assay for forebrain abnormalities (Morris 1984). Morris water maze training was performed as described previously (Onozuka et al 1999;Watanabe et al 2002;Kubo et al 2005). A stainless steel tank with 90 cm in diameter and 30 cm in depth was filled with water (approximately 26°C) to a height of 16 cm, and the water surface was covered with floating polystyrene foam granules (approximately 2 mm in diameter).…”

Section: Morris Water Maze Leaning Testmentioning

confidence: 99%

“…Recent studies suggest that deterioration of the oral environment causes various effects on the central nervous system, such as a decrease of spine numbers in the hippocampal CA1 area , an increase of plasma corticosterone (Yoshihara et al 2001), and transient activation of microglia (Kojo et al 2010). Furthermore, masticatory disorders reduce input activities in the hippocampus, thereby leading to deficits in learning and memory in aged senescence-accelerated prone 8 mice (Onozuka et al 1999(Onozuka et al , 2000Kubo et al 2005). In this report, we investigated the effects of increasing the occlusal vertical dimension on the mouse amygdaloid and hippocampal dynorphinergic nervous system using immunohistochemical, biochemical and behavioral techniques.…”

Section: Introductionmentioning

confidence: 99%

Occlusal Disharmony Transiently Impairs Learning and Memory in the Mouse by Increasing Dynorphin A Levels in the Amygdala

Yamada

Ono

Kubo

et al. 2013

Tohoku J. Exp. Med.

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Occlusal disharmony sometimes causes not only stiffness of neck but also psychiatric depression, suggesting that the condition of oral cavity may affect the central nervous system. Dynorphin A is an endogenous opioid peptide that specifically binds the κ-opioid receptor and has a protective role against stress. Dynorphinergic nervous system is intensely distributed in the amygdala and hippocampus that are coping areas with stress. As a model of malocclusion, we placed dental resin on the molars to increase the occlusal vertical dimension (bite-raise). After various survival times, we analyzed the amygdala and hippocampus by immunohistochemistry and immunosorbent assay (ELISA). Furthermore, the effects on learning and memory were assessed by Morris water maze test. In the amygdala, the levels of dynorphin A were increased on the 1st day after increasing the vertical dimension as indicated by immunohistochemical and ELISA assessments. The levels of dynorphin A returned to control levels on the 5th day. In the hippocampus, there were no noticeable changes in dynorphin A levels. The water maze test indicated that increasing the vertical dimension caused longer escape latency times on the 3rd day compared to those of sham-operated group. However, the bite-raised mice treated with a dynorphin antagonist, nor-binaltorphimine, showed similar escape latency times to the times of sham-operated group, even on the 3rd day. These results suggest that occlusal disharmony causes stress resulting in a transient increase of dynorphin A levels at least in the amygdala and that the increased dynorphin A levels transiently impair learning and memory.

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Neuroplastic changes in the sensorimotor cortex associated with orthodontic tooth movement in rats

Sood

Lee

Avivi‐Arber

et al. 2015

J of Comparative Neurology

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Orthodontic tooth movement (OTM) causes transient pain and changes in the dental occlusion that may lead to altered somatosensory inputs and patterns of mastication. This study used intracortical microstimulation (ICMS) and electromyographic (EMG) recordings to test whether neuroplastic changes occur in the ICMS-defined motor representations of left and right anterior digastric (LAD, RAD), masseter, buccinator, and genioglossus (GG) muscles within the rat's face primary motor cortex (face-M1) and adjacent face primary somatosensory cortex (face-S1) during OTM. Analyses included any changes in the number of ICMS sites representing these muscles and in the onset latencies of ICMS-evoked responses in the muscles. Sprague-Dawley rats were divided into experimental (E), sham (S), and naive (N) groups; OTM was induced in the E group. Statistical analyses involved a mixed model repeated-measures analysis of variance (MMRM ANOVA). OTM resulted in significant neuroplastic changes in the number of positive sites in the E group for LAD, RAD, and GG muscles in face-M1 and face-S1 at days 1, 7, and 28 of continuous orthodontic force application, and in the number of sites in face-M1 from which ICMS could simultaneously evoke EMG responses in different combinations of LAD, RAD, and GG muscles. However, the onset latencies of ICMS-evoked responses were not significantly different between groups or between face-M1 and face-S1. The neuroplastic changes documented in this study may reflect adaptive sensorimotor changes in response to the altered environment in the oral cavity induced by OTM.

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Reduced mastication stimulates impairment of spatial memory and degeneration of hippocampal neurons in aged SAMP8 mice

Cited by 157 publications

References 23 publications

Influences of reduced masticatory sensory input from soft-diet feeding upon spatial memory/learning ability in mice

Influences of reduced masticatory sensory input from soft-diet feeding upon spatial memory/learning ability in mice

Occlusal Disharmony Transiently Impairs Learning and Memory in the Mouse by Increasing Dynorphin A Levels in the Amygdala

Neuroplastic changes in the sensorimotor cortex associated with orthodontic tooth movement in rats

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