Deletion of Snap25 disrupts glial remodeling in aging mouse brain

Neuronal activity regulates glial physiology, but the effects of prolonged synaptic silencing in mature circuits are unclear. Using Rbp4-Cre-mediated Snap25 deletion to block neurotransmitter release in subsets of cortical layer 5 neurons and dentate gyrus granule cells, we examined glial responses across connected brain regions and the spinal cord in adult and middle-aged mice. Silenced cortical regions showed strong astrocytic reactivity and increased microglial density, while downstream targets, including the superior colliculus and CA3, exhibited marked microglial remodeling and synaptic changes. CA1 displayed milder alterations. In the spinal cord, microglial density decreased and GFAP⁺ astrocytes increased, whereas TNF-α levels and ChAT⁺ motor neurons were unchanged. Age amplified astrocyte heterogeneity and microglial reactivity under synaptic silencing. These findings suggest that circuit topology shapes the spatial and cellular specificity of glial responses to chronic loss of synaptic activity.