Low-Dose Digoxin Ameliorates Age-Related Motor Learning Deficits in Mice.

Age-related decline in motor learning has been linked to impaired synaptic plasticity in the central nervous system; however, effective pharmacological strategies to restore these processes remain limited. Here, we investigated whether low-dose digoxin improves motor learning performance and dendritic spine structural plasticity in the middle-aged mice. Behavioral analyses revealed that low-dose digoxin (4 and 65 µg/kg) enhanced motor learning performance in the rotarod task, without affecting muscle strength or spontaneous locomotor activity. At the molecular level, digoxin increased sodium-potassium ATPase (Na/K ATPase) activity in the motor cortex. Morphological analyses using Golgi-Cox staining demonstrated a selective increase in filopodia and thin-type dendritic spines, which are associated with structural remodeling. Interestingly, these changes occurred without a detectable increase in the brain-derived neurotrophic factor (BDNF) protein level in the motor cortex as assessed by western blotting. Given the established role of BDNF in synaptic plasticity, these findings suggest that the observed structural changes are not primarily mediated by the BDNF upregulation. Instead, the data are consistent with engagement of activity-dependent structural remodeling pathways, including the neurotrypsin-agrin pathway, which links synaptic activity to dendritic filopodia formation. Furthermore, agrin-derived fragments have been reported to interact with Na/K ATPase, suggesting that this fragment may function as a molecular interface between extracellular signaling and synaptic structural remodeling. Together, these results indicate that modulation of Na/K ATPase activity enhances motor learning and dendritic spine remodeling in the aged motor cortex through mechanisms that do not require increased BDNF protein levels.