Effects of cardiac glycoside digoxin on dendritic spines and motor learning performance in mice

Abstract

Abstract Synapse formation following the generation of postsynaptic dendritic spines is essential for motor learning and functional recovery after brain injury. The C -terminal fragment of agrin cleaved by neurotrypsin induces dendritic spine formation in the adult hippocampus. Since the α3 subunit of sodium-potassium ATPase (Na/K ATPase) is a neuronal receptor for agrin in the central nervous system, cardiac glycosides might facilitate dendritic spine formation and subsequent improvements in learning. This study investigated the effects of the cardiac glycoside digoxin on dendritic spine turnover and learning performance in mice. Golgi-Cox staining revealed that intraperitoneal injection of digoxin less than its IC50 in brain significantly increased the density of long spines (≥2 µm) in cerebral cortex and hippocampus in wild-type mice and neurotrypsin-knockout (NT-KO) mice showing impairment of activity-dependent spine formation. Whereas motor learning performance of NT-KO mice showed significantly lower than control wild-type mice under the control condition, low dose of digoxin enhanced performance to a similar degree in both strains. In NT-KO mice, lower doses of digoxin equivalent to clinical doses also significantly improved performance. These data suggest that lower doses of digoxin could modify dendritic spine formation or recycling and facilitate motor learning in compensation for the neurotrypsin-agrin pathway.