Hippocampal viscosity is increased when estrogen is low in female rats scanned with MR elastography

Motivation: We aimed to study parallel changes in tissue mechanics and astrocytic response as a novel mechanism linking hormonal state to brain tissue properties, particularly relevant to understanding cognitive vulnerability during menopause when estrogen levels decline dramatically. Goal(s): This study evaluated how estrogen modulates hippocampal tissue mechanics and astrocytic composition in female rats. Approach: Using repeated magnetic resonance elastography, we found that low estrogen states lead to increased hippocampal damping ratio, indicating reduced tissue viscosity. Results: These mechanical changes coincide with elevated astrocytic estrogen receptor expression and reduced astrocyte population. Impact: We reveal a previously unknown relationship between estrogen and brain tissue mechanics, demonstrating that hormonal changes directly influence hippocampal viscoelasticity through astrocytic mechanisms, providing new therapeutic targets for maintaining cognitive health during menopause and aging.