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

Abstract

Summary: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 proteinlabeled 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.

Spatial memory decline after masticatory deprivation and aging is associated with altered laminar distribution of CA1 astrocytes

“…The systemic effects of long-term masticatory imbalances are associated with neurodegeneration and are a risk factor for senile dementia in humans [4] and memory deficits in experimental animals [5]. To investigate the impact of masticatory imbalances on various activities and physiological factors, experimental masticatory deprivation has been modelled experimentally in animals using a modified diet [6], molar removal [7,8], or occlusion disharmony modelled by "bite-raised" condition [9,10]. These approaches revealed that masticatory dysfunction reduces spatial learning and memory in water maze tests in rats [8,11] and mice [11-13], and that these deficits seem to increase with aging and time after tooth loss [8].…”

Enriched environment and masticatory activity rehabilitation recover spatial memory decline in aged mice

“…SAMP8 mice reach adult maturity at 6 months of age when learning and memory deficits become apparent in a variety of behavioural tests [42-45] and when reduced masticatory activity accelerates age-related learning and memory decline [40]. Occlusal disharmony also aggravates age-dependent deficits in spatial learning in the Morris water maze [17,46-49]; see [13,40] for recent reviews. Moreover, monkey studies demonstrate that when occlusal disharmony is removed, the associated stressful response disappears [50].…”