A single, subanesthetic dose of ketamine improved reward responsiveness in both humans with treatment-resistant depression and chronically-stressed rats, measured using functionally identical tasks. The finding suggests that ketamine's rapid antidepressant effects may involve enhancing reward processing, a core feature of anhedonia. The work provides translational evidence linking preclinical and clinical observations, though the mechanisms remain unclear.
Psilocybin and ketamine acutely increased reward responsiveness in rats, and the effect persisted 24 hours after dosing. The increase from psilocybin, but not ketamine, was blocked by a 5-HT2A receptor antagonist. Other psychedelics, DMT and DOI, also acutely increased reward responsiveness but the effect did not last 24 hours. The non-psychedelic 5-HT2A agonist lisuride and the SSRI fluoxetine had no positive effects. These results suggest psychedelics can produce acute and enduring increases in reward responsiveness, partly through the 5-HT2A receptor, though the time course varies and clinical implications require further validation.