Antidepressant-like effects of a novel 5-HT₃ receptor antagonist 6z in acute and chronic murine models of depression

Aim: To investigate the antidepressant-like effects of a novel 5-HT₃ receptor antagonist N-(benzo[d]thiazol-2-yl)-3-methoxyquinoxalin-2-carboxamide (6z) in acute and chronic murine models of depression. Methods: 5-HT₃ receptor antagonism was examined in guinea pig ileum in vitro. A tail suspension test (TST) was used as acute depression model to evaluate the antidepressant-like behavior in mice treated with 6z (0.5-2 mg/kg, ip). In chronic depression model, mice were exposed to a 4-week chronic unpredictable stress (CUS) protocol, and treated with 6z (0.5-2 mg·kg^-1·d^-1, po) or a positive drug fluoxetine (10 mg·kg^-1·d^-1, po) in the last 2 weeks, followed by behavioral and biochemical assessments. Results: The 5-HT₃ receptor antagonism of 6z (pA₂=7.4) in guinea pig ileum was more potent than that of a standard 5-HT₃ receptor antagonist ondansetron (pA₂=6.9). In acute depression model, 6z administration significantly decreased the immobility duration. In chronic depression model, 6z administration reversed CUS-induced depressive-like behavior, as evidenced by increased immobility duration in the forced swim test and sucrose preference in the sucrose preference test. Furthermore, chronic administration of 6z prevented CUS-induced brain oxidative stress, with significant reduction of pro-oxidant markers and elevation of antioxidant enzyme activity. Moreover, chronic administration of 6z attenuated CUS-induced hypothalamic-pituitary-adrenal axis hyperactivity, as shown by reduced plasma corticosterone levels. Similar results were observed in the fluoxetine-treated group. Conclusion: 6z is a novel 5-HT₃ receptor antagonist with potential antidepressant-like activities, which may be related to modulating hypothalamic-pituitary-adrenal axis and attenuating brain oxidative damage.