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

Abstract

BackgroundChewing imbalances are associated with neurodegeneration and are risk factors for senile dementia in humans and memory deficits in experimental animals. We investigated the impact of long-term reduced mastication on spatial memory in young, mature and aged female albino Swiss mice by stereological analysis of the laminar distribution of CA1 astrocytes. A soft diet (SD) was used to reduce mastication in the experimental group, whereas the control group was fed a hard diet (HD). Assays were performed in 3-, 6- and 18-month-old SD and HD mice.ResultsEating a SD variably affected the number of astrocytes in the CA1 hippocampal field, and SD mice performed worse on water maze memory tests than HD mice. Three-month-old mice in both groups could remember/find a hidden platform in the water maze. However, 6-month-old SD mice, but not HD mice, exhibited significant spatial memory dysfunction. Both SD and HD 18-month-old mice showed spatial memory decline. Older SD mice had astrocyte hyperplasia in the strata pyramidale and oriens compared to 6-month-old mice. Aging induced astrocyte hypoplasia at 18 months in the lacunosum-moleculare layer of HD mice.ConclusionsTaken together, these results suggest that the impaired spatial learning and memory induced by masticatory deprivation and aging may be associated with altered astrocyte laminar distribution and number in the CA1 hippocampal field. The underlying molecular mechanisms are unknown and merit further investigation.

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

“…A number of studies using a variety of behavioural assays, including the Morris water maze [18,19,31-36], passive avoidance [37], and radial arm maze [20,38,39], indicate that long-term soft-diet feeding or extraction of molar teeth results in learning and memory deficits [40]. Recent studies with the Morris water maze demonstrated that mice fed a hard diet required significantly less time to reach the platform than experimental mice and spent significantly more time in the former platform area, suggesting that hard-diet feeding is associated with improved spatial memory [41].…”

“…Recent studies with the Morris water maze demonstrated that mice fed a hard diet required significantly less time to reach the platform than experimental mice and spent significantly more time in the former platform area, suggesting that hard-diet feeding is associated with improved spatial memory [41]. In addition, one-year-old [35] or 18-month-old [36] adult mice fed with a soft diet, compared to a solid-diet group, showed lower spatial performances on the Morris water maze. Similarly, SAMR1 and SAMP8 mice fed a solid diet performed better in the eight-arm radial maze than mice fed a powdered diet [39].…”

“…Experimental approaches imposing masticatory deprivation, like tooth-loss [20], long-term soft diet [21], or bite-rise occlusion, suggest a behavioural displacement, but more research is needed into the effects of rehabilitation. Here we examined outcomes at the intersection of masticatory deprivation, environmental conditions, and spatial memory impairments in adult (6-month-old; 6M) and aged (18-month-old; 18M) mice.…”

Efecto de la masticación sobre la memoria y aprendizaje espacial en ratones adultos y seniles

“…Cada grupo etario se dividió por aleatorización en 2 subgrupos de 8 animales cada uno. El número de ratones por cada subgrupo experimental se definió en base a investigaciones que trabajaron variables similares 11,13,[16][17][18] .…”

“…Por otra parte, se ha relacionado la ausencia de piezas dentarias con un mayor riesgo de aparición de deterioro cognitivo e incluso de demencia 9 . Estudiándose, también en humanos, que un menor estímulo masticatorio incrementa la percepción de estímulos nociceptivos 10 , y además, produce un deterioro evidente de las funciones de memoria y aprendizaje tanto en diseños experimentales en humanos como en animales 5,[11][12][13] , resaltándose que la falta de estímulo masticatorio en ratonas embarazadas sometidas a estrés produjo alteraciones cognitivas en su descendencia 14,15 .…”