Increase in Serotonin Turnover and Anxiolytic Effects Following 14-Day Intracerebroventricular Ouabain Infusion in C57BL/6 Mice

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.