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.

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.

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.

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.

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.

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.

Environmental enrichment improves hypomyelination, synaptic alterations, and memory deficits caused by tooth loss in aged SAMP8 mice.

OBJECTIVE: Prolonged mild stress due to tooth loss leads to morphologic and functional alterations of the hippocampus, as well as cognitive memory impairments in aged animals. An enriched environment improves stress-induced hippocampus-dependent cognitive impairments. The potential mechanisms underlying the beneficial effects of an enriched environment, however, remain unclear. In the present study, we investigated whether an enriched environment affects morphologic remodeling of the hippocampal myelin, synapses, and spatial learning deficits caused by tooth loss in aged senescence-accelerated mouse strain P8 (SAMP8) mice. DESIGN: SAMP8 mice (8 months old) with either teeth intact or teeth extracted were raised in a standard or enriched environment for three weeks. Spatial learning and memory ability was evaluated in a Morris water maze test. The morphologic features of the myelin sheath and synapses in the hippocampus were investigated by electron microscopy. RESULTS: Mice with tooth loss had a thinner myelin sheaths and shorter postsynaptic densities in the hippocampal CA1 region, and impaired hippocampus-dependent spatial learning ability. Exposure to an enriched environment ameliorated the hypomyelination and synaptic alterations, and spatial learning and memory impairments induced by tooth loss in aged SAMP8 mice. CONCLUSION: Our findings indicate that an enriched environment ameliorates hippocampal hypomyelination and synapse morphologic abnormalities, as well as learning deficits induced by tooth loss in aged SAMP8 mice.

Root-crown ratios of permanent teeth in healthy and young Hungarian, German, and Japanese populations / A maradó fogak gyökér-korona aránya egészséges, fiatal magyar, német és japán populációkban.

Összefoglaló. Bevezetés: A maradó fogak gyökér-korona arányának meghatározása nagy jelentoséggel bír a fogászati kezelési terv kialakításában és késobbi módosításában. Célkituzés: Egészséges magyar, német és japán fiatalok maradó fogai gyökér-korona arányának meghatározása és összehasonlítása. Módszer: Hölttä módszerét alkalmaztuk. A mérés 95 magyar, 104 japán és 110 német fiatal páciens 2001 és 2006 között készült panorámaröntgen-felvételén történt. Eredmények: A gyökér-korona arány különbsége a nemek között nem szignifikáns, az egymásnak megfelelo antagonista fogak között sok esetben, de nem mindig, szignifikáns. A legnagyobb gyökér-korona arányt mindhárom populációban az alsó szemfogakon és az alsó második praemolaris fogakon mértük; a felso molarisok esetén a legkisebb az arány. A három nemzetet összehasonlítva szignifikáns különbséget (p≤0,001) nem találtunk egyetlen fogtípus esetében sem. A japán és a német populáció között minden fogtípus esetén szignifikáns volt a különbség a gyökér-korona arányokban. A japán és a magyar populáció összehasonlításakor a fogtípusok felénél találtunk szignifikáns különbséget. A magyar és a német populációt összehasonlítva nagyon kevés fogtípusnál találtunk szignifikáns különbséget. Megbeszélés: Az alsó állcsont fogainak gyökér-korona arányértékei nagyobb mértékben térnek el a populációk között, mint a felso állcsont fogainak esetében. A gyökér-korona arány átlagértéke a német populációban a legnagyobb. A második legnagyobb arányértékkel a magyar populáció rendelkezik, utána pedig a japán, néhány fogtípus kivételével: felso kismetszok, felso szemfogak és felso elso molarisok. Következtetés: A legnagyobb gyökér-korona arány különbséget a német és a japán populáció között, a legkisebbet a magyar és a német populáció között találtuk. Cikkünk megmutatja az egyes fogtípusok gyökér-korona arányának normálértékét fiatal, egészséges magyar, német és japán populációban. Orv Hetil. 2021; 162(46): 1848-1855. INTRODUCTION: Defining the root-crown ratio of the permanent teeth is important in making or changing proper treatment plans in dentistry. OBJECTIVE: To define and compare the root-crown ratios of the permanent teeth of healthy, young Hungarian, German, and Japanese populations. METHOD: We adapted Hölttä's method. 95 Hungarian, 104 Japanese and 110 German young patients' panoramic X-rays (made between 2001 and 2006) were involved in the investigation. RESULTS: Difference between the genders was found non-significant; between the corresponding antagonists many times, but not all significant. The highest root-crown ratios were found in all investigated populations by the lower canines and premolars, the lowest by the upper molars. P≤0,001 was not found among the three populations. Significant differences were found between Japanese and German populations by all tooth-types; between Japanese and Hungarian populations by near half of the tooth-types; between Hungarian and German populations by only a few tooth-types. DISCUSSION: More significant differences were found in root-crown ratios in the lower jaw among the populations. The mean value of the root-crown ratios was the highest in the German population; medium in the Hungarian population; and the least in the Japanese population, with a few exceptions: upper lateral incisors, canines and first molars. CONCLUSION: The biggest differences were found between the German and Japanese populations; the least between the Hungarian and the German populations. Our paper describes the control values of the root-crown ratios of the tooth types in young, healthy Hungarian, German, and Japanese populations. Orv Hetil. 2021; 162(46): 1848-1855.

Maternal chewing improves prenatal stress-induced cognitive deficit and anxiety-like behavior associated with alterations of the apoptotic response and serotonin pathway in mouse offspring.

OBJECTIVE: To examine whether maternal chewing affects prenatal stress-induced behavioral alternations associated with the changes in apoptosis-related proteins and serotonin pathway of the mouse offspring. DESIGN: Pregnant mice were assigned to control, stress, and stress/chewing groups. Stress mice were placed in restraint tubes, from gestational day 12 until parturition. Stress/chewing mice were given a wooden stick for chewing during stress period. Morris water maze and hole-board tests were applied for behavioral alterations in one-month-old male pups. Hippocampal mRNA expression of B-cell lymphoma 2 (Bcl-2) and Bcl-2 associated X protein (Bax) was analyzed by quantitative real-time PCR. Serotonin and tryptophan hydroxylase expression level in the dorsal raphe nucleus was investigated immunohistochemically. RESULTS: Prenatal stress impaired the spatial learning, induced anxiety-like behavior, increased the ratio of hippocampal Bax/Bcl-2 expression, and decreased the expression of serotonin and tryptophan hydroxylase in dorsal raphe nucleus of the offspring. Maternal chewing ameliorated prenatal stress-induced cognitive impairment, anxiety-like behavior, and attenuated the increased ratio of hippocampal Bax/Bcl-2 expression, and the downregulated serotonin signaling in dorsal raphe nucleus of the offspring. CONCLUSIONS: Our results indicate that maternal chewing could improve prenatal stress-related anxiety-like behavior and cognitive impairment in mouse offspring, at least in part by affecting hippocampal apoptotic response and central serotonin pathway.

Chewing Behavior Attenuates the Tumor Progression-Enhancing Effects of Psychological Stress in a Breast Cancer Model Mouse.

We examined whether chewing behavior affects the tumor progression-enhancing impact of psychological stress. Human breast cancer cell line (MDA-MB-231) cells were inoculated into the mammary fat pads of athymic nude mice. The mice were assigned randomly to control, stress, and stress+chewing groups. Psychological stress was created by keeping mice in a transparent restraint cylinder for 45 min, three times a day, for 35 days after cell inoculation. Animals in the stress+chewing group were provided with a wooden stick for chewing on during the psychological stress period. Chewing behavior remarkably inhibited the tumor growth accelerated by the psychological stress. Immunohistochemical and Western blot findings revealed that chewing behavior during psychological stress markedly suppressed tumor angiogenesis and cell proliferation. In addition, chewing behavior decreased serum glucocorticoid levels and expressions of glucocorticoid and ß2-adrenergic receptors in tumors. Chewing behavior decreased expressions of inducible nitric oxide synthase and 4-hydroxynonenal, and increased expression of superoxide dismutase 2 in tumors. Our findings suggest that chewing behavior could ameliorate the enhancing effects of psychological stress on the progression of breast cancer, at least partially, through modulating stress hormones and their receptors, and the subsequent signaling pathways involving reactive oxygen and nitrogen species.

Masticatory function and cognitive function.

Recent studies have suggest that masticatory (chewing) function is useful for maintaining neurocognitive function in the elderly. For example, a reduced ability to masticate, such as that resulting from toothlessness or soft-diet feeding, causes learning and memory deficits in aged animals and pathologic changes in the hippocampus. In addition, occlusal disharmony impairs hippocampal memory processes via chronic stress, and induces similar hippocampal pathology. Chewing, however, rescues stress-induced suppression of long-term potentiation in the hippocampus and the stress-induced impairment of hippocampal-dependent learning. These findings strongly suggest a link between mastication and neurocognitive function.

A Case of Anaphylaxis in Which a Basophil Activation Test Was Used to Identify the Suspected Agent.

This is a case report of anaphylaxis in which the basophil activation test (BAT) was used to identify the etiological agent. Although skin tests are considered the most effective methods for identifying anaphylactic triggers, the test itself presents a risk of inducing anaphylaxis. The BAT is advantageous because of its inherent lack of risk, high sensitivity and specificity to identify the suspected anaphylactic agents, and diagnostic accuracy comparable to conventional skin testing. Therefore, in the future, the BAT is likely to become the preferred test for the detection of allergens over conventional skin tests.

Vulnerability to stress in mouse offspring is ameliorated when pregnant dams are provided a chewing stick during prenatal stress.

OBJECTIVE: To investigate whether maternal chewing during prenatal stress alters the responsivity of young offspring to novel stress, we examined the expression of hippocampal glucocorticoid receptors and mineralocorticoid receptors, and the levels of hypothalamic corticotropin-releasing hormone in young adult mouse offspring of dams exposed to restraint stress during pregnancy. DESIGN: To induce stress, the dams were placed in a ventilated restraint tube for 45 min each day from day 12 of pregnancy through parturition. While restrained in the tube, one group of dams was provided a wooden stick for chewing. Hippocampal expression of glucocorticoid receptor and mineralocorticoid receptor messenger ribonucleic acid was assessed in 1-month-old pups. Hypothalamic expression of corticotropin-releasing hormone messenger ribonucleic acid was examined before and after exposing the offspring to a novel stressor. RESULTS: Prenatal stress significantly decreased hippocampal expression of both glucocorticoid receptor and mineralocorticoid receptor messenger ribonucleic acid in the offspring, and increased the expression of corticotropin-releasing hormone messenger ribonucleic acid in the hypothalamic paraventricular nucleus in the offspring after novel stress exposure. Maternal chewing during exposure to prenatal stress attenuated the decreased hippocampal expression of both glucocorticoid receptor and mineralocorticoid receptor messenger ribonucleic acid, and the increased corticotropin-releasing hormone messenger ribonucleic acid expression in the hypothalamic paraventricular nucleus in the offspring. CONCLUSIONS: Downregulation of hippocampal glucocorticoid receptor and mineralocorticoid receptor expression in offspring due to prenatal stress, which may be associated with increased susceptibility to novel stress in adulthood, are attenuated by allowing the dams to chew on a wooden stick.

Malocclusion induces chronic stress.

We examined the effect of occlusal disharmony in senescence-accelerated (SAMP8) mice on plasma corticosterone levels, spatial learning in the water maze, fos induction, hippocampal neuron number, expression of glucocorticoid receptors (GR) and glucocorticoid receptor messenger ribonucleic acid (GRmRNA) in hippocampus and inhibitor of glucocorticoid (metyrapone). Bite-raised aged mice had significantly greater plasma corticosterone levels than age-matched control mice as well as impaired spatial memory and decreased Fos induction and a number of neurons in hippocampus. GR and GRmRNA expressions were significantly decreased in aged bite-raised mice compared with age-matched control mice. Pretreatment with metyrapone inhibited not only the bite-raised induced increase in plasma corticosterone levels, but also the reduction in the number of hippocampal neurons and impaired spatial learning. These datas suggest that the bite-raised condition may enhance the aging process in hippocampus, thereby leading to impairment of spatial memory by stress.

The bite-raised condition enhances the aging process in the dorsal and ventral hippocampus.

The bite raised condition decreases the number of neurons and increases the amount of glial fibrillary acidic protein in the hippocampus of aged SAMP8 mice. In the present study, we examined whether these effects differ between the dorsal and ventral hippocampus. In bite-raised SAMP8 mice, the number of neurons was significantly lower in the hippocampal CA1 and dentate gyrus (DG) subfields compared to control mice. In the bite raised condition, the number of neurons was significantly lower in both the dorsal and ventral CA3 subfields, and the number of glial fibrillary acidic protein-labeled astrocytes was increased in the CA1, CA3, and DG subfields, compared to control mice. These data suggest that in aged SAMP8 mice, the bite-raised condition enhanced aging processes in both the dorsal and ventral hippocampus.

The bite-raised condition in aged SAMP8 mice reduces the expression of glucocorticoid receptors in the dorsal and ventral hippocampus.

In the present study, we examined whether the effects induced by the bite-raised condition on glucocorticoid receptor (GR) expression differ between the dorsal and ventral hippocampus in SAMP8 mice. In the bite-raised condition, the number of GR-immunoreactive cells was significantly decreased in both the dorsal and ventral CA1 and dentate gyrus (DG) subfields of the hippocampus compared to control mice, as revealed by immunohistochemical analysis. The decrease in the number of GR-immunoreactive cells tended to be greater in the dorsal hippocampus than in the ventral hippocampus. Only in the DG subfield was there a significant difference in the number of GR-immunoreactive cells between the dorsal and ventral hippocampus. These findings suggest that in aged SAMP8 mice, the bite-raised condition decreases the number of GR-immunoreactive cells in both the dorsal and ventral hippocampus.

Occlusal disharmony induces spatial memory impairment and hippocampal neuron degeneration via stress in SAMP8 mice.

We examined the effect of occlusal disharmony in senescence-accelerated (SAMP8) mice on plasma corticosterone levels, hippocampal neuron number, and spatial performance in the water maze. The bite-raised condition was associated with an accelerated age-related decline in spatial memory, increased plasma corticosterone levels, and a decreased number of neurons in the hippocampal CA3 region. The findings suggest that the bite-raised condition in aged SAMP8 mice induces hippocampal neuron loss, thereby leading to senile memory deficits.