Tooth loss early in life induces hippocampal morphology remodeling in senescence-accelerated mouse prone 8 (SAMP8) mice.

Long-term tooth loss is associated with the suppression of hippocampal neurogenesis and impairment of hippocampus-dependent cognition with aging. The morphologic basis of the hippocampal alterations, however, remains unclear. In the present study, we investigated whether tooth loss early in life affects the hippocampal ultrastructure in senescence-accelerated mouse prone 8 (SAMP8) mice, using transmission electron microscopy. Male SAMP8 mice were randomized into control or tooth-loss groups. All maxillary molar teeth were removed at 1 month of age. Hippocampal morphologic alterations were evaluated at 9 months of age. Tooth loss early in life induced mitochondrial damage and lipofuscin accumulation in the hippocampal neurons. A thinner myelin sheath and decreased postsynaptic density length were also observed. Our results revealed that tooth loss early in life may lead to hippocampal ultrastructure remodeling and subsequent hippocampus-dependent cognitive impairment in SAMP8 mice with aging.

Effects of Maternal Chewing on Prenatal Stress-Induced Cognitive Impairments in the Offspring via Multiple Molecular Pathways.

We aimed to investigate the effects of maternal chewing on prenatal stress-induced cognitive impairments in the offspring and to explore the molecular pathways of maternal chewing in a mice model. Maternal chewing ameliorated spatial learning impairments in the offspring in a Morris water maze test. Immunohistochemistry and Western blot findings revealed that maternal chewing alleviated hippocampal neurogenesis impairment and increased the expression of hippocampal brain-derived neurotrophic factor in the offspring. In addition, maternal chewing increased the expression of glucocorticoid receptor (GR) and 11ß-hydroxysteroid dehydrogenase isozyme 2 (11ß-HSD2) and decreased the expression of 11ß-HSD1 in the placenta, thereby attenuating the increase of glucocorticoid in the offspring. Furthermore, maternal chewing increased the expression of 11ß-HSD2, FK506-binding protein 51 (FKBP51) and FKBP52 and decreased the expression of 11ß-HSD1, thereby increasing hippocampal nuclear GR level. In addition, maternal chewing attenuated the increase in expression of DNMT1 and DNMT3a and the decrease in expression of histone H3 methylation at lysine 4, 9, 27 and histone H3 acetylation at lysine 9 induced by prenatal stress in the offspring. Our findings suggest that maternal chewing could ameliorate prenatal stress-induced cognitive impairments in the offspring at least in part by protecting placenta barrier function, alleviating hippocampal nuclear GR transport impairment and increasing the hippocampal brain-derived neurotrophic factor (BDNF) level.

Yokukansan Ameliorates Hippocampus-Dependent Learning Impairment in Senescence-Accelerated Mouse.

Yokukansan (YKS) is a traditional Japanese herbal medicine. It has been currently applied for treating behavioral and psychological symptoms of dementia in Japan. We investigated the effect of YKS on learning ability, hippocampal cell proliferation, and neural ultrastructural features in senescence-accelerated mouse prone 8 (SAMP8), a proposed animal model of Alzheimer's disease. Five-month-old male SAMP8 mice were randomly assigned to control and experimental groups. The control group had drug-free water ad libitum. The experimental mice were given 0.15% aqueous solution of YKS orally for eight weeks. Learning ability was assessed in Morris water maze test. Hippocampal cell proliferation was investigated using bromodeoxyuridine immunohistochemical method. The neural ultrastructural features, including myelin sheath and synapse, were investigated electron microscopy. Administration with YKS improved the hippocampal cell proliferation in dentate gyrus, and ameliorated learning impairment in SAMP8 mice. Numerous lipofuscin inclusions were presented in hippocampal neurons of the control mice. However, little were found after treatment with YKS. Myelin sheath was thicker and postsynaptic density length was longer after treatment with YKS. Administration with YKS ameliorated learning impairment in SAMP8 mice, mediated at least partially via delaying neuronal aging process, neurogenesis, myelin sheath and synaptic plasticity in the hippocampus. These results suggest that YKS might be effective for preventing hippocampus-dependent cognitive deficits with age.

Chewing during prenatal stress prevents prenatal stress-induced suppression of neurogenesis, anxiety-like behavior and learning deficits in mouse offspring.

Prenatal stress (PS) induces learning deficits and anxiety-like behavior in mouse pups by increasing corticosterone levels in the dam. We examined the effects of maternal chewing during PS on arginine vasopressin (AVP) mRNA expression in the dams and on neurogenesis, brain-derived neurotrophic factor (BDNF) mRNA expression, learning deficits and anxiety-like behavior in the offspring. Mice were divided into control, stress and stress/chewing groups. Pregnant mice were exposed to restraint stress beginning on day 12 of pregnancy and continuing until delivery. Mice in the stress/chewing group were given a wooden stick to chew during restraint stress. PS significantly increased AVP mRNA expression in the paraventricular nucleus (PVN) of the hypothalamus in the dams. PS also impaired learning ability, suppressed neurogenesis and BDNF mRNA expression in the hippocampus, and induced anxiety-like behavior in the offspring. Chewing during PS prevented the PS-induced increase in AVP mRNA expression of the PVN in the dams. Chewing during PS significantly attenuated the PS-induced learning deficits, anxiety-like behavior, and suppression of neurogenesis and BDNF mRNA expression in the hippocampus of the offspring. Chewing during PS prevented the increase in plasma corticosterone in the dam by inhibiting the hypothalamic-pituitary-adrenal axis activity, and attenuated the attenuated the PS-induced suppression of neurogenesis and BDNF expression in the hippocampus of the pups, thereby ameliorating the PS-induced learning deficits and anxiety-like behavior. Chewing during PS is an effective stress-coping method for the dam to prevent PS-induced deficits in learning ability and anxiety-like behavior in the offspring.

Morphological and molecular characterization of the senile osteoporosis in senescence-accelerated mouse prone 6 (SAMP6).

Although the understanding of the complex pathogenesis for osteoporosis is appreciable, the underlying mechanism is not yet fully elucidated. There is a great need to further characterize the available animal models in osteoporosis research. The senescence-accelerated mouse prone 6 (SAMP6) mice have been developed as the spontaneous experimental model for senile osteoporosis. Here, we provide a comprehensive overview of current research regarding the bone morphological and molecular alterations and the possible mechanisms involved in these changes. There were significant decrease in trabecular bone mass at the axial and appendicular skeletal sites, with no marked alterations of cortical bone. Decreased bone formation on the endosteal surface and trabecular bone, and increased bone marrow adiposity were observed in SAMP6 mice. The elevated expression level of proliferator activator gamma (PPARγ) in the bone marrow suggest that PPARγ might regulate osteoblastic bone formation negatively in SAMP6 mice. The expression level of secreted frizzled-related protein 4 (Sfrp4) was found to be higher in SAMP6 mice. Sfrp4 is considered to suppress osteoblastic proliferation mediated by inhibition of Wnt signaling pathway. These findings may help us to gain more insight into the potential mechanism of senile osteoporosis.

Maternal Active Mastication during Prenatal Stress Ameliorates Prenatal Stress-Induced Lower Bone Mass in Adult Mouse Offspring.

Chronic psychological stress is a risk factor for osteoporosis. Maternal active mastication during prenatal stress attenuates stress response. The aim of this study is to test the hypothesis that maternal active mastication influences the effect of prenatal stress on bone mass and bone microstructure in adult offspring. Pregnant ddY mice were randomly divided into control, stress, and stress/chewing groups. Mice in the stress and stress/chewing groups were placed in a ventilated restraint tube for 45 minutes, 3 times a day, and was initiated on day 12 of gestation and continued until delivery. Mice in the stress/chewing group were allowed to chew a wooden stick during the restraint stress period. The bone response of 5-month-old male offspring was evaluated using quantitative micro-CT, bone histomorphometry, and biochemical markers. Prenatal stress resulted in significant decrease of trabecular bone mass in both vertebra and distal femur of the offspring. Maternal active mastication during prenatal stress attenuated the reduced bone formation and increased bone resorption, improved the lower trabecular bone volume and bone microstructural deterioration induced by prenatal stress in the offspring. These findings indicate that maternal active mastication during prenatal stress can ameliorate prenatal stress-induced lower bone mass of the vertebra and femur in adult offspring. Active mastication during prenatal stress in dams could be an effective coping strategy to prevent lower bone mass in their offspring.

Association between Mastication, the Hippocampus, and the HPA Axis: A Comprehensive Review.

Mastication is mainly involved in food intake and nutrient digestion with the aid of teeth. Mastication is also important for preserving and promoting general health, including hippocampus-dependent cognition. Both animal and human studies indicate that mastication influences hippocampal functions through the end product of the hypothalamic-pituitary-adrenal (HPA) axis, glucocorticoid (GC). Epidemiologic studies suggest that masticatory dysfunction in aged individuals, such as that resulting from tooth loss and periodontitis, acting as a source of chronic stress, activates the HPA axis, leading to increases in circulating GCs and eventually inducing various physical and psychological diseases, such as cognitive impairment, cardiovascular disorders, and osteoporosis. Recent studies demonstrated that masticatory stimulation or chewing during stressful conditions suppresses the hyperactivity of the HPA axis via GCs and GC receptors within the hippocampus, and ameliorates chronic stress-induced hippocampus-dependent cognitive deficits. Here, we provide a comprehensive overview of current research regarding the association between mastication, the hippocampus, and HPA axis activity. We also discuss several potential molecular mechanisms involved in the interactions between mastication, hippocampal function, and HPA axis activity.

Chewing Maintains Hippocampus-Dependent Cognitive Function.

Mastication (chewing) is important not only for food intake, but also for preserving and promoting the general health. Recent studies have showed that mastication helps to maintain cognitive functions in the hippocampus, a central nervous system region vital for spatial memory and learning. The purpose of this paper is to review the recent progress of the association between mastication and the hippocampus-dependent cognitive function. There are multiple neural circuits connecting the masticatory organs and the hippocampus. Both animal and human studies indicated that cognitive functioning is influenced by mastication. Masticatory dysfunction is associated with the hippocampal morphological impairments and the hippocampus-dependent spatial memory deficits, especially in elderly. Mastication is an effective behavior for maintaining the hippocampus-dependent cognitive performance, which deteriorates with aging. Therefore, chewing may represent a useful approach in preserving and promoting the hippocampus-dependent cognitive function in older people. We also discussed several possible mechanisms involved in the interaction between mastication and the hippocampal neurogenesis and the future directions for this unique fascinating research.

Effects of Active Mastication on Chronic Stress-Induced Bone Loss in Mice.

Chronic psychologic stress increases corticosterone levels, which decreases bone density. Active mastication or chewing attenuates stress-induced increases in corticosterone. We evaluated whether active mastication attenuates chronic stress-induced bone loss in mice. Male C57BL/6 (B6) mice were randomly divided into control, stress, and stress/chewing groups. Stress was induced by placing mice in a ventilated restraint tube (60 min, 2x/day, 4 weeks). The stress/chewing group was given a wooden stick to chew during the experimental period. Quantitative micro-computed tomography, histologic analysis, and biochemical markers were used to evaluate the bone response. The stress/chewing group exhibited significantly attenuated stress-induced increases in serum corticosterone levels, suppressed bone formation, enhanced bone resorption, and decreased trabecular bone mass in the vertebrae and distal femurs, compared with mice in the stress group. Active mastication during exposure to chronic stress alleviated chronic stress-induced bone density loss in B6 mice. Active mastication during chronic psychologic stress may thus be an effective strategy to prevent and/or treat chronic stress-related osteopenia.

Tooth loss early in life accelerates age-related bone deterioration in mice.

Both osteoporosis and tooth loss are health concerns that affect many older people. Osteoporosis is a common skeletal disease of the elderly, characterized by low bone mass and microstructural deterioration of bone tissue. Chronic mild stress is a risk factor for osteoporosis. Many studies showed that tooth loss induced neurological alterations through activation of a stress hormone, corticosterone, in mice. In this study, we tested the hypothesis that tooth loss early in life may accelerate age-related bone deterioration using a mouse model. Male senescence-accelerated mouse strain P8 (SAMP8) mice were randomly divided into control and toothless groups. Removal of the upper molar teeth was performed at one month of age. Bone response was evaluated at 2, 5 and 9 months of age. Tooth loss early in life caused a significant increase in circulating corticosterone level with age. Osteoblast bone formation was suppressed and osteoclast bone resorption was activated in the toothless mice. Trabecular bone volume fraction of the vertebra and femur was decreased in the toothless mice with age. The bone quality was reduced in the toothless mice at 5 and 9 months of age, compared with the age-matched control mice. These findings indicate that tooth loss early in life impairs the dynamic homeostasis of the bone formation and bone resorption, leading to reduced bone strength with age. Long-term tooth loss may have a cumulative detrimental effect on bone health. It is important to take appropriate measures to treat tooth loss in older people for preventing and/or treating senile osteoporosis.

The osteocyte plays multiple roles in bone remodeling and mineral homeostasis.

Osteocytes are the most abundant cells in bone and are the major orchestrators of bone remodeling and mineral homeostasis. They possess a specialized cellular morphology and a unique molecular feature. Osteocytes are a stellate shape with numerous long, slender dendritic processes. The osteocyte cell body resides in the bone matrix of the lacuna and the dendritic processes extend within the canaliculi to adjacent osteocytes and other cells on the bone surface. Osteocytes form extensive intercellular network to sense and respond to environmental mechanical stimulus by the lacunar-canalicular system and gap junction. Osteocytes are long-lived bone cells. They can undergo apoptosis, which may have specific regulatory effects on osteoclastic bone resorption. Osteocytes can secrete several molecules, including sclerostin, receptor activator of nuclear factor κB ligand and fibroblast growth factor 23 to regulate osteoblastic bone formation, osteoclastic bone resorption and mineral homeostasis. A deeper understanding of the complex mechanisms that mediate the control of osteoblast and osteoclast function by osteocytes may identify new osteocyte-derived molecules as potential pharmacological targets for treating osteoporosis and other skeletal diseases.

Chronic Psychological Stress as a Risk Factor of Osteoporosis.

Osteoporosis, the most common metabolic skeletal disease, is characterized by decreased bone mass and deteriorated bone quality, leading to increased fracture risk. With the aging of the population, osteoporotic fracture is an important public health issue. Organisms are constantly exposed to various stressful stimuli that affect physiological processes. Recent studies showed that chronic psychological stress is a risk factor for osteoporosis by various signaling pathways. The purpose of this article is to review the recent progress of the association between chronic psychological stress and osteoporosis. Increasing evidence confirms the physiological importance of the central nervous system, especially the hypothalamus, in the regulation of bone metabolism. Both animal and human studies indicate that chronic psychological stress induces a decrease of bone mass and deterioration of bone quality by influencing the hypothalamic-pituitary-adrenocortical (HPA) axis, sympathetic nervous system, and other endocrine, immune factors. Active mastication, proven to be an effective stress-coping behavior, can attenuate stress-induced neuroendocrine responses and ameliorate stress-induced bone loss. Therefore, active mastication may represent a useful approach in preventing and/or treating chronic stress-associated osteoporosis. We also discuss several potential mechanisms involved in the interaction between chronic stress, mastication and osteoporosis. Chronic stress activates the HPA axis and sympathetic nervous system, suppresses the secretion of gonadal hormone and growth hormone, and increases inflammatory cytokines, eventually leading to bone loss by inhibiting bone formation and stimulating bone resorption.

Effects of early tooth loss on chronic stress and progression of neuropathogenesis of Alzheimer's disease in adult Alzheimer's model AppNL-G-F mice.

Introduction: Alzheimer's disease (AD), the most common neurodegenerative disease, is characterized by accumulated amyloid-ß (Aß) plaques, aggregated phosphorylated tau protein, gliosis-associated neuroinflammation, synaptic dysfunction, and cognitive impairment. Many cohort studies indicate that tooth loss is a risk factor for AD. The detailed mechanisms underlying the association between AD and tooth loss, however, are not yet fully understood. Methods: We explored the involvement of early tooth loss in the neuropathogenesis of the adult AppNL-G-F mouse AD model. The maxillary molars were extracted bilaterally in 1-month-old male mice soon after tooth eruption. Results: Plasma corticosterone levels were increased and spatial learning memory was impaired in these mice at 6 months of age. The cerebral cortex and hippocampus of AD mice with extracted teeth showed an increased accumulation of Aß plaques and phosphorylated tau proteins, and increased secretion of the proinflammatory cytokines, including interleukin 1ß (IL-1ß) and tumor necrosis factor α (TNF-α), accompanied by an increased number of microglia and astrocytes, and decreased synaptophysin expression. AD mice with extracted teeth also had a shorter lifespan than the control mice. Discussion: These findings revealed that long-term tooth loss is a chronic stressor, activating the recruitment of microglia and astrocytes; exacerbating neuroinflammation, Aß deposition, phosphorylated tau accumulation, and synaptic dysfunction; and leading to spatial learning and memory impairments in AD model mice.

Effects of exercise after focal cerebral cortex infarction on basal ganglion.

Identification of functional molecules in the brain related to improvement of motor dysfunction after stroke will contribute to establish a new treatment strategy for stroke rehabilitation. Hence, monoamine changes in basal ganglion related to motor control were examined in groups with/without voluntary exercise after cerebral infarction. Cerebral infarction was produced by photothrombosis in rats. Voluntary exercise using a running wheel was initiated from 2 days after surgery. Motor performance was measured by the accelerated rotarod test. Monoamine concentrations in striatum were analyzed using HPLC and immunohistochemical staining performed with anti-tyrosine hydroxylase antibody. In behavioral evaluation, the mean latency until falling from the rotating rod in the group with exercise (infarction-EX group) was significantly longer than that in the group without exercise (infarction-CNT group). When concerning the alteration of monoamine concentration between before and 2 days after infarction, dopamine level showed a significant increase 2 days after infarction. Subsequently, dopamine level was significantly decreased in the infarction-EX group at 10 days after infarction; in contrast, both norepinephrine and 5-HT concentrations were significantly higher in the infarction-EX group than in the infarction-CNT group. Furthermore, duration of rotarod test showed a significant inverse correlation with dopamine levels and a significant positive correlation with 5-HT levels. In immunohistochemical analysis, tyrosine hydroxylase immunoreactivity in substantia nigra pars compacta was shown to increase in the infarction-CNT group. In the present study, at least some of the alterations of monoamines associated with the improvement of paralysis in the basal ganglion related to motor control might have been detected.

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

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.

Maternal chewing alleviates prenatal stress-related neuroinflammation mediated by microglia in the hippocampus of the mouse offspring.

PURPOSE: Prenatal stress affects the hippocampal structure and function in pups. Maternal chewing ameliorates hippocampus-dependent cognitive impairments induced by prenatal stress. In this study, we investigated hippocampal microglia-mediated neuroinflammation in pups of dams exposed to prenatal stress with or without chewing during gestation. METHODS: Pregnant mice were randomly assigned to control, stress, and stress/chewing groups. Stress and stress/chewing animals were subjected to restraint stress for 45 min three times daily from gestation day 12 to parturition, and were given a wooden stick to chew during the stress period. Four-month-old male pups were intraperitoneally administered with lipopolysaccharide (LPS). Serum corticosterone levels were determined 24 h after administration. The expression levels of hippocampal inflammatory cytokines were measured, and the microglia were analyzed morphologically. RESULTS: Prenatal stress increased serum corticosterone levels, induced hippocampal microglia priming, and facilitated the release of interleukin-1ß and tumor necrosis factor-α in the offspring. LPS treatment significantly increased the effects of prenatal stress on serum corticosterone levels, hippocampal microglial activation, and hippocampal neuroinflammation. Maternal chewing significantly inhibited the increase in serum corticosterone levels, suppressed microglial overactivation, and normalized inflammatory cytokine levels under basal prenatal stress conditions as well as after LPS administration. CONCLUSIONS: Our findings indicate that maternal chewing can alleviate the increase in corticosterone levels and inhibit hippocampal microglia-mediated neuroinflammation induced by LPS administration and prenatal stress in adult offspring.

Double inferior vena cava with interiliac vein: a case report and literature review.

The duplication of the inferior vena cava (IVC) is a rare, but well-recognized anomaly. Duplicated IVC has a significant relevance for retroperitoneal surgery and venous interventional radiology. We report a case of duplicated IVC, which was observed during routine dissection of an 84-year-old Japanese female cadaver. The interiliac vein between the duplicated IVC ran obliquely upwards from left to right. We performed systematic literature review of published reports based on Pubmed and Medline from 1967 to 2011. Of 109 cases with IVC anomalies identified by the literature search, 22 cases (20.2%) displayed no interiliac anastomosis. The interiliac vein connecting duplicated IVC existed in 74 cases (67.9%). According to the running direction of the interiliac vein, we found that the vein ran from left to right in 42 cases, coursed from right to left in 19 cases, and ran horizontally in 13 cases. Thirteen left IVC displayed symmetrical-to-normal connection with the bilateral common iliac veins. Awareness of these venous variations is necessary to reduce surgical risk and to determine strategy in interventional radiology.

Chewing Behavior Attenuates Lung-Metastasis-Promoting Effects of Chronic Stress in Breast-Cancer Lung-Metastasis Model Mice.

We assessed the effects of chewing behavior on the lung-metastasis-promoting impact of chronic psychological-stress in mice. Human breast-cancer cells (MDA-MB-231) were injected into the tail vein of female nude mice. Mice were randomly divided into stress, stress-with-chewing, and control groups. We created chronic stress by placing mice in small transparent tubes for 45 min, 3 times a day for 7 weeks. Mice in the stress-with-chewing group were allowed to chew wooden sticks during the experimental period. The histopathological examination showed that chronic psychological-stress increased lung metastasis, and chewing behavior attenuated the stress-related lung metastasis of breast-cancer cells. Chewing behavior decreased the elevated level of the serum corticosterone, normalized the increased expression of glucocorticoid, and attenuated the elevated expression of adrenergic receptors in lung tissues. We also found that chewing behavior normalized the elevated expression of inducible nitric oxide synthase, 4-hydroxynonenal, and superoxide dismutase 2 in lung tissues, induced by chronic stress. The present study demonstrated that chewing behavior could attenuate the promoting effects of chronic psychological-stress on the lung metastasis of breast-cancer cells, by regulating stress hormones and their receptors, and the downstream signaling-molecules, involving angiogenesis and oxidative stress.

Deletion of Wnt10a Is Implicated in Hippocampal Neurodegeneration in Mice.

The hippocampus plays an important role in maintaining normal cognitive function and is closely associated with the neuropathogenesis of dementia. Wnt signaling is relevant to neuronal development and maturation, synaptic formation, and plasticity. The role of Wnt10a in hippocampus-associated cognition, however, is largely unclear. Here, we examined the morphological and functional alterations in the hippocampus of Wnt10a-knockout (Wnt10a-/-) mice. Neurobehavioral tests revealed that Wnt10a-/- mice exhibited spatial memory impairment and anxiety-like behavior. Immunostaining and Western blot findings showed that the protein expressions of ß-catenin, brain-derived neurotrophic factor, and doublecortin were significantly decreased and that the number of activated microglia increased, accompanied by amyloid-ß accumulation, synaptic dysfunction, and microglia-associated neuroinflammation in the hippocampi of Wnt10a-/- mice. Our findings revealed that the deletion of Wnt10a decreased neurogenesis, impaired synaptic function, and induced hippocampal neuroinflammation, eventually leading to hippocampal neurodegeneration and memory deficit, possibly through the ß-catenin signaling pathway, providing a novel insight into preventive approaches for hippocampus-dependent cognitive impairment.

Relationship between light and dark period activity cycles and oral condition in senescence-accelerated mice.

We investigated the effect of tooth absence and masticatory abnormalities due to powdered food feeding starting during the juvenile period on light and dark period activity cycles in senescence-accelerated mice (SAMP1). SAMP1 were divided into 5 groups: Group 1, maxillo-mandibular molar tooth extraction; Group 2, maxillary molar tooth extraction; Group 3, mandibular molar tooth extraction; Group 4, powdered food; and Group 5, sham-operated control. Senescence was observed earliest in the powdered food group. Total 24-hour activity was higher in the control group than in the four other groups. In the powdered food group, the dark period activity decreased to less than 60% of the total activity in the 36th week. In the tooth extraction groups (Groups 1-3), dark period activity decreased to less than 60% of the total activity in the 40th week. The control group dark period activity remained above 60% for the entire experimental period. Thus, the distinction between the light and dark periods disappeared earlier in the four experimental groups compared with the control group. Significant correlations were noted among total activity, degree of senescence, and percent dark period activity in each experimental group. Functional masticatory insufficiency promoted dementia and behavioral abnormalities in SAMP1.