Pre-amyloid cognitive intervention preserves brain function in aged TgF344-AD rats, maintaining connectivity and enhancing plasticity in a sex-specific manner

Abstract

BackgroundAlzheimers disease is characterized by progressive cognitive decline and neurodegeneration, with cognitive reserve playing a key role in mitigating disease impact. Cognitive stimulation has been suggested as a non-pharmacological approach to enhance cognitive reserve and delay cognitive deterioration, but its underlying mechanism remains to be fully understood. This study investigates the effects of pre-amyloid cognitive intervention on brain connectivity, memory, synaptic plasticity and neuroinflammation in aged TgF344-AD rats, considering sex-specific differences. MethodsMale and female TgF344-AD and wild-type rats were assigned to trained and untrained groups, with cognitive stimulation administered through repetitive delayed nonmatch-to-sample tasks. Longitudinal magnetic resonance imaging acquisitions assessed training-induced changes in whole-brain functional connectomics and in particular entorhinal cortex connectivity. Memory was evaluated using the novel object recognition test. Cellular analysis of neurons (NeuN+, Parvalbumin+) and microglial cells, as well as molecular (PSD95, TrkB, p-RPS6, and VGLUT) analyses were conducted to determine the role of cognitive stimulation in modulating neuronal density, neuroinflammation and neuroplasticity. ResultsMale TgF344-AD rats undergoing prolonged cognitive stimulation had preserved global functional connectivity and exhibited improved recognition memory, compared to untrained animals, while TgF344-AD females did not follow this pattern. Entorhinal cortex connectivity was significantly loss in 19-month-old rats compared to wild-type rats and this was completely prevented by training. At a cellular level, cognitive stimulation significantly decreased the number of PV+ neurons in the dentate gyrus of trained rats. Moreover, a greater microglial density around A{beta} plaques and a less reactive phenotype was clearly observed at 11 in trained rats. These protective effects diminished by 19 months, coinciding with increased neuroinflammation and microglial dysfunction. At a molecular level, cognitive stimulation preserved PSD95 expression in male TgF344-AD and p-RPS6 in both sexes. ConclusionsPre-amyloid cognitive stimulation enhances synaptic plasticity, sustains brain network integrity, and modulates neuroinflammation, contributing to increased resilience against Alzheimers disease-related cognitive decline. In general, cognitive stimulation exerted a more protective effect in male TgF344-AD rats showing sex-dependent differences in pathology and cognitive reserve mechanisms. These findings highlight the importance of early cognitive engagement as a potential strategy to delay disease onset and underscore sex-specific differences in cognitive resilience mechanisms.