The Role of Astrocytes in the Temporoammonic Pathway: Masticatory Behavior as a Neuroprotective Strategy Against Age-Related Cognitive Decline

Astrocytes undergo phenotypic changes with aging, contributing to neurodegenerative diseases and cognitive impairments in later life. The temporoammonic (TA) pathway terminates at the stratum lacunosum-moleculare (SLM) of the CA1 region, where astrocytic support is crucial for synaptic plasticity and information processing related to spatial learning and memory. This study tested the hypothesis that age-related morphological changes in astrocytes of the SLM affect cognitive performance and we explored whether masticatory activity modulates these changes. Young (6 months) and aged (18 months) female Swiss albino mice were subjected to three distinct masticatory regimens: a hard diet (HD), HD followed by a soft diet (HD/SD), or HD followed by SD and a return to HD (HD/SD/HD). Cognitive performance was assessed using the Morris Water Maze (MWM), with learning rates calculated from escape latencies throughout five days of trials. After behavioral testing, the mice were culled and immunohistochemical analysis of glial fibrillary acidic protein (GFAP) expression was performed. 3D reconstructions of astrocytes within the SLM were generated and analyzed. Hierarchical clustering identified distinct astrocyte morphotypes, revealing a significant age-related shift from high-complexity astrocytes (AST1) toward lower-complexity subtypes (AST2 and AST3. The results demonstrate that aging reduces astrocytic complexity, especially in the dorsal CA1 region, which correlated with impaired spatial learning and memory. Notably, mice on the HD/SD/HD regimen exhibited partial recovery of cognitive function and astrocytic morphology, suggesting a potential rehabilitation effect from masticatory activity. Statistical analysis confirmed significant differences in cognitive performance and astrocytic complexity across age groups and dietary regimens (p < 0.01). These findings highlight that the morphological changes in astrocytes within the SLM may contribute to age-related cognitive decline. Overall, maintaining proper mastication may be an effective approach to maintain astrocytic integrity during aging and preserve hippocampus-dependent cognitive function, particularly in older individuals.