Molarless-induced changes of spines in hippocampal region of SAMP8 mice.
ABSTRACT We examined the effect of the molarless condition on the dendritic spines of hippocampal pyramidal cells in SAMP8 mice in comparison to its effect on learning ability in a maze test. The molarless condition caused a decrease in the number of the spines of CA1 pyramidal cells only in the aged mice showing a reduced learning ability. The results suggest the involvement of the molarless condition in an attenuation of input activities in the hippocampal synapses.
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ABSTRACT: 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.Neuroscience Letters 04/2007; 414(2):188-91. · 2.03 Impact Factor
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ABSTRACT: Research in animals and humans has shown that mastication maintains cognitive function in the hippocampus, a brain area important for learning and memory. Reduced mastication, an epidemiological risk factor for the development of dementia in humans, attenuates spatial memory and causes hippocampal neurons to deteriorate morphologically and functionally, especially in aged animals. Active mastication rescues the stress-attenuated hippocampal memory process in animals and attenuates the perception of stress in humans by suppressing endocrinological and autonomic stress responses. Active mastication further improves the performance of sustained cognitive tasks by increasing the activation of the hippocampus and the prefrontal cortex, the brain regions that are essential for cognitive processing. Abnormal mastication caused by experimental occlusal disharmony in animals produces chronic stress, which in turn suppresses spatial learning ability. The negative correlation between mastication and corticosteroids has raised the hypothesis that the suppression of the hypothalamic-pituitary-adrenal (HPA) axis by masticatory stimulation contributes, in part, to preserving cognitive functions associated with mastication. In the present review, we examine research pertaining to the mastication-induced amelioration of deficits in cognitive function, its possible relationship with the HPA axis, and the neuronal mechanisms that may be involved in this process in the hippocampus.Journal of Oral Rehabilitation 03/2010; 37(8):624-40. · 2.34 Impact Factor
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ABSTRACT: The molarless condition has been reported to compromise learning and memory functions. However, it remains unclear how the molarless condition directly affects the central nervous system, and the functional consequences on the brain cortex and hippocampus have not been described in detail. The aim of this study was to find the molecular mechanism related with learning and memory deficit after a bilateral molarless condition having been surgically induced in senescence-accelerated mice/prone 8 (SAMP8) mice, which may ultimately provide an experimental basis for clinical prevention of senile dementia. Mice were either sham-operated or subjected to complete molar removal. The animals' body weights were monitored every day. Learning ability and memory were measured in a water maze test at the end of the 1st, 2nd, and 3rd months after surgery. As soon as significantly prolonged escape latency in the molarless group was detected, the locomotor activity was examined in an open field test. Subsequently, the animals were decapitated and the cortex and hippocampus were dissected for Western blotting to measure the expression levels of brain-derived neurotrophic factor (BDNF) and the tropomyosin related kinase B (TrkB), the high affinity receptor of BDNF. Slightly lower weights were consistently observed in the molarless group, but there was no significant difference in weights between the two groups (P > 0.05). Compared with the sham group, the molarless group exhibited lengthened escape latency in the water maze test three months after surgery, whereas no difference in locomotor activity was observed. Meanwhile, in the cortex and hippocampus, BDNF levels were significantly decreased in the molarless group (P < 0.05); but the expression of its receptor, TrkB, was not significantly affected. These results suggested that the molarless condition impaired learning and memory abilities in SAMP8 mice three months after teeth extraction, and this effect was accompanied by significantly reduced BDNF expression in the cortex and hippocampus.Chinese medical journal 05/2011; 124(10):1540-4. · 0.90 Impact Factor