Background: Ketamine exerts a robust, rapid, and relatively sustained antidepressant effect in patients with major depression. Understanding the mechanisms underlying the intriguing effects of N-methyl d-aspartate (NMDA) antagonists could lead to novel treatments with a rapid onset of action.
Methods: The learned helplessness, forced swim, and passive avoidance tests were used to investigate ketamine's behavioral effects in mice. Additional biochemical and behavioral experiments were undertaken to determine whether the antidepressant-like properties of ketamine and other NMDA antagonists involve alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor throughput.
Results: Subanesthetic doses of ketamine treatment caused acute and sustained antidepressant-like effects. At these doses, ketamine did not impair fear memory retention. MK-801 (dizocilpine) and Ro25-6981, an NR2B selective antagonist, also exerted antidepressant-like effects; these effects, however, were not sustained as long as those of ketamine. Pre-treatment with NBQX, an AMPA receptor antagonist, attenuated both ketamine-induced antidepressant-like behavior and regulation of hippocampal phosphorylated GluR1 AMPA receptors.
Conclusions: NMDA antagonists might exert rapid antidepressant-like effects by enhancing AMPA relative to NMDA throughput in critical neuronal circuits.