Objective: Ouabain, a cardiotonic steroid, induces hyperactivity mediated by alterations in dopamine turnover in the central nervous system. However, ouabain, a cardiotonic steroid, induces hyperactivity mediated by alterations in dopamine turnover in the central nervous system. However, the effects of prolonged ouabain administration remain poorly studied. Methods: Adult C57BL/6 mice received 20 μM ouabain via intracerebroventricular (ICV) infusion using 14-day osmotic pumps. Nest building was assessed on day 14 as a measure of general well-being. On day 15, locomotor activity was evaluated in square open field arenas; anxiety-like behavior was evaluated using the elevated plus maze. Brain regions including the cerebellum, frontal cortex, striatum, hippocampus, thalamus, and brain stem were collected for neurochemical analysis using high-performance liquid chromatography. Results: Chronic ICV ouabain led to elevated serotonin levels in the frontal cortex, thalamus, and hippocampus, and reduced noradrenaline in the thalamus. These changes were accompanied by decreased anxiety-like behavior and impaired nest building, without significant effects on locomotion. These effects differ from those observed following acute ICV ouabain injection, which affects dopamine turnover but not serotonin levels, causing an increase in locomotor activity and decrease in anxiety-like behavior. Conclusions: Unlike acute ICV ouabain administration, which alters dopamine turnover and induces persistent hyperactivity, sustained low-dose exposure elevates serotonin and reduces anxiety-like behavior unaccompanied by locomotor activation. These findings suggest that ouabain’s effects on anxiety and hyperactivity are mediated by different mechanisms, through alterations in serotonin and dopamine, respectively.

Cardiotonic steroids (CTS) can modulate central nervous system function through their interaction with the Na⁺,K⁺-ATPase, affecting dopaminergic transmission. While the CTS ouabain is known to induce mania-like behavior and oxidative damage, the effects of other CTS are less clear. This study examined the effects of 14-day intracerebroventricular administration of 1.5 μl 100 μM marinobufagenin (MBG) on locomotion, gait, monoamine metabolism, and oxidative stress markers (MDA, SOD, catalase, MAO-B) in C57BL/6 mice. Chronic MBG caused increased locomotor activity and time spent in the center of the open field. Unlike ouabain, chronic MBG did not impair motor function, evaluated via gait analysis. MBG elevated striatal MAO-B activity and reduced prefrontal MDA levels, with no changes in SOD or catalase, indicating that it did not cause oxidative stress. However, it did affect dopamine and serotonin metabolism. Monoamine tissue content evaluation on day 15 showed increased dopamine turnover in the striatum and brain stem, and decreased it in the thalamus. Norepinephrine levels increased in the striatum and hippocampus. Serotonin turnover increased in the prefrontal cortex. These results indicate that chronic MBG increases locomotion and reduces anxiety-like behavior through region-specific modulation of dopaminergic and serotonergic signaling distinct from that caused by ouabain.

Cardiotonic steroids (CTS) can modulate central nervous system function through their interaction with the Na⁺,K⁺-ATPase, affecting dopaminergic transmission. While the CTS ouabain is known to induce mania-like behavior and oxidative damage, the effects of other CTS are less clear. This study examined the effects of 14-day intracerebroventricular administration of 1.5 μL 100 μM marinobufagenin (MBG) on locomotion, gait, monoamine metabolism, and oxidative stress markers (MDA, SOD, catalase, MAO-B) in C57BL/6 mice. Chronic MBG caused increased locomotor activity and time spent in the center of the open field. Unlike ouabain, chronic MBG did not impair motor function, evaluated via gait analysis. MBG elevated striatal MAO-B activity and reduced prefrontal MDA levels, with no changes in SOD or catalase, indicating that it did not cause oxidative stress. However, it did affect dopamine and serotonin metabolism. Monoamine tissue content evaluation on day 15 showed increased dopamine turnover in the striatum and brain stem, and a decrease in the thalamus. Norepinephrine levels increased in the striatum and hippocampus. Serotonin turnover increased in the prefrontal cortex. These results indicate that chronic MBG increases locomotion and reduces anxiety-like behavior through region-specific modulation of dopaminergic and serotonergic signaling distinct from that caused by ouabain.