Inhibition of SERT and NMDAR synergistically confers rapid antidepressant effects of ketamine

-methyl-d-aspartate receptor (NMDAR) blockade is crucial for the rapid antidepressant effects of ketamine, the involvement of other mechanisms remains contentious, particularly regarding the role of serotonin, a key neurotransmitter in the target of traditional antidepressants. Here, we demonstrate that ketamine elevates serotonin levels by inhibiting the serotonin transporter (SERT). A cryogenic electron microscopy structure of ketamine-bound SERT in the outward-open conformation, resolved at 3.2 Å, indicates that ketamine binds to the central site of SERT. Elevated serotonin, along with NMDAR inhibition, induces ketamine-like rapid antidepressant effects. This increase in serotonin leads to the activation of vasoactive intestinal peptide (VIP)-expressing interneurons, which are essential for the rapid antidepressant effects of ketamine. Inhibition of VIP neurons blocks these effects and ketamine-like effects, highlighting a crucial cell type-specific mechanism. These findings identify a critical pathway in the rapid antidepressant actions of ketamine and offer potential pharmacological strategies for developing rapidly acting antidepressants.