Chronic administration of a positive allosteric modulator at the alpha5-GABAA receptor reverses age-related dendritic shrinkage
Over the last 15 years, worldwide life expectancy increased by 5 years jumping from 66 years to 71 years. With progress in science, medicine, and care we tend to live longer. Such extended life expectancy is still associated with age-related changes, including in the brain. The aging brain goes through various changes that can be called morphomolecular senescence. Overall, the brain volume changes, neuronal activity is modified and plasticity of the cells diminishes, sometimes leading to neuronal atrophy and death. Altogether, these changes contribute to the emergence of cognitive decline that still does not have an efficient treatment available. Many studies in the context of cognitive decline focused on pathological aging, targeting beta-amyloid in Alzheimer's disease, for example. However, beta-amyloid plaques are also present in healthy adults and treatments targeting plaques have failed to improve cognitive functions. In order to improve the quality of life of aging population, it is crucial to focus on the development of novel therapies targeting different systems altered during aging, such as the GABAergic system. In previous studies, it has been shown that positive allosteric modulators (PAM) acting at the alpha5-containing GABA-A receptors improve cognitive performances, and that these alpha5-GABA-A receptors are implicated in dendritic growth of pyramidal neurons. Here, we hypothesized that targeting the alpha5-GABA-A receptors could contribute to the reduction of cognitive decline, directly through activity of the receptors, and indirectly by increasing neuronal morphology. Using primary neuronal culture and chronic treatment in mice, we demonstrated that an alpha5-PAM increased dendritic length, spine count and spine density in brain regions involved in cognitive processes (prefrontal cortex and hippocampus). We also confirmed the procognitive efficacy of the alpha5-PAM and showed that the washout period diminishes the precognitive effects without altering the effect on neuronal morphology. Future studies will be needed to investigate what downstream mechanisms responsible for the neurotrophic effect of the alpha5-PAM.
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