A growing body of evidence has suggested that the dysfunction of glutamatergic systems plays a pivotal role in major depressive disorder (MDD). In clinical studies, an N-methyl-d-aspartate receptor antagonist, ketamine, was shown to exert both rapid and sustained antidepressant effects in patients with treatment-resistant MDD. The objective of the present study was to confirm the rapid onset of action of ketamine and to investigate the mechanisms underlying both the rapid and sustained antidepressant-like effects of ketamine in rodent models of depression. The intraperitoneal administration of ketamine (10mg/kg) 30min prior to testing significantly reduced the number of escape failures in the learned helplessness (LH) paradigm in rats in which currently prescribed antidepressants exerted an effect only after repeated administrations. Ketamine also significantly reduced the immobility time in the tail suspension test (TST), and this effect lasted for 72h, indicating that ketamine may possess a sustained antidepressant-like effect. The rapid antidepressant-like effects of ketamine in both the LH paradigm and the TST were significantly blocked by subcutaneous treatment with 2,3-dihydroxy-6-nitro-7-sulfoamoylbenzo(f)quinoxaline (NBQX), an α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor antagonist. In addition, the sustained antidepressant-like effect of ketamine in the TST was partially abolished by treatment with NBQX. In conclusion, we confirmed the faster onset of the action of ketamine, compared with clinically prescribed antidepressants. Moreover, the present results suggested that direct AMPA receptor activation may play an important role in both the rapid and sustained antidepressant-like effects of ketamine in animal models of depression, although other mechanisms might be involved in the sustained action.
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