A study in Molecular Psychiatry used PET imaging with a new tracer to track changes in AMPA-type glutamate receptors in people with treatment-resistant depression receiving ketamine, reporting that region-specific receptor changes were associated with symptom improvement.
Major depressive disorder is a leading cause of disability worldwide, and a substantial minority of patients do not respond adequately to standard antidepressant treatments.
In a study published March 5, 2026, in Molecular Psychiatry, a Japan-based research team led by Professor Takuya Takahashi of Yokohama City University’s Graduate School of Medicine used positron emission tomography (PET) to examine AMPA-type glutamate receptors (AMPAR) in the living human brain before and after ketamine treatment.
The researchers used a PET tracer known as [¹¹C]K-2, which is designed to measure AMPAR availability on the neuronal cell surface. The analysis combined data from three clinical studies conducted in Japan and registered under jRCTs031210124, UMIN000025132, and jRCTs031200083. According to the journal article, the trials were conducted between August 2016 and October 2023.
The main ketamine study involved adults with treatment-resistant depression who received ketamine or placebo during a blinded period, with PET scans performed before and after treatment. The paper reports baseline PET data from 34 participants with treatment-resistant depression, with comparisons to healthy participants drawn from the other studies.
Across brain regions, the researchers reported that AMPAR measures differed between patients with treatment-resistant depression and healthy participants in some areas. They also found that the relationship between ketamine-related receptor changes and clinical improvement varied by region. In reward-related circuitry that included the habenula, the paper reports that greater ketamine-associated reductions in AMPAR measures were linked to larger improvements in depression ratings; the study also notes that baseline habenula tracer uptake did not differ between the treatment-resistant depression group and healthy participants.
Takahashi said the work helps address a long-standing gap in human data on ketamine’s rapid antidepressant action. “Although ketamine has shown rapid antidepressant effects in patients with treatment-resistant depression, its molecular mechanism in the human brain has remained unclear,” he said in a university statement.
In the same statement, Takahashi added that the team’s imaging approach enabled them to visualize changes in AMPAR distribution after ketamine and to relate those changes to symptom improvement.
The authors and the university statement describe the findings as direct human evidence consistent with earlier animal research implicating AMPAR-related mechanisms in ketamine’s antidepressant effects. The study also suggests that AMPAR PET imaging could eventually help identify biological markers linked to treatment response, though further work would be needed to determine how well such measures predict outcomes in broader clinical settings.
