Summary: Ketamine can deliver rapid relief for some people with treatment-resistant depression, but its side effects and short-lived benefits have limited clinical use. Two recent studies have mapped precisely how ketamine produces its antidepressant effect and used that knowledge to recreate its benefits in mice with combinations of lower-dose drugs. These findings point to new rapid-acting antidepressant strategies that avoid the dissociative “trip” and many adverse effects.
Researchers identified specific opioid receptors on interneurons in the prefrontal cortex and a novel interaction between cell-surface receptors that together explain both the fast onset and the longer-lasting benefits of ketamine. Using this mechanistic insight, teams have demonstrated ways to reproduce ketamine’s therapeutic action with existing, better-tolerated drugs and are moving toward clinical testing.
Key Facts
- Cortical reawakening: Ketamine briefly suppresses certain inhibitory interneurons in the medial prefrontal cortex by engaging opioid receptors, lifting a brake on neural circuits and producing a rapid reactivation of prefrontal networks.
- Triple-drug strategy: In one study, researchers reproduced ketamine’s rapid antidepressant-like effect in mice by combining low doses of three drugs that target the same pathway, achieving synergy while avoiding high-dose side effects such as dissociation and blood pressure spikes.
- Maintaining the effect: Long-term antidepressant benefit requires coordinated signaling between the TrkB receptor (activated by BDNF) and the metabotropic glutamate receptor mGluR5, a form of receptor “cross-talk” that stabilizes strengthened synapses.
- Synaptic strengthening and protection: BDNF-driven TrkB signaling enhances communication between cells and triggers removal of some mGluR5 receptors from the cell membrane, reducing the capacity for those receptors to later weaken synapses.
- Accelerated translation: Because the drug combinations under study use compounds already approved or tested in humans, clinical trials are being planned to evaluate whether these lower-dose regimens can safely reproduce ketamine’s benefits in patients.
Source: Weill Cornell University
Weill Cornell Medicine researchers have reverse-engineered how ketamine produces its antidepressant effects to reveal new treatment strategies.
Depression affects brain circuits and does not respond to standard therapies in a substantial fraction of patients. Roughly a third of people with depression require multiple medication trials to find relief, and many experience treatment-resistant depression. Ketamine, an anesthetic with rapid antidepressant properties, can relieve symptoms in some of these patients almost immediately, but the benefit often fades and the drug can cause cardiovascular changes, dissociation and addictive behaviors in vulnerable individuals.
“We urgently need new options,” said Dr. Conor Liston, a psychiatry and neuroscience professor at Weill Cornell Medicine. “By pinpointing how ketamine works, we aimed to replicate its therapeutic effects without the problematic side effects.”
How ketamine triggers the rapid antidepressant response
Prior work suggested opioid receptors are involved in ketamine’s actions. To identify the precise targets, Dr. Liston teamed with Dr. Joshua Levitz to map the receptors and cell types that mediate ketamine’s early effects. Their study, published in Cell, shows ketamine acts on mu-opioid receptors concentrated in somatostatin-expressing interneurons of the medial prefrontal cortex. These interneurons normally inhibit pyramidal neurons and regulate cortical output.
Under chronic stress, these interneurons become hyperactive and over-suppress prefrontal activity, a change linked to depressive symptoms. Ketamine transiently dampens interneuron activity via these opioid receptors, briefly releasing inhibition and allowing pyramidal neurons to reactivate—what the authors describe as a cortical “reawakening.” Although the window of disinhibition may last only 15 to 20 minutes, it appears sufficient to trigger downstream processes that initiate antidepressant responses.
Building on that insight, the team showed that a low-dose combination of three drugs targeting the same pathway produced similar behavioral benefits in mice. Because each drug can be given at a lower dose, the combination reduces the likelihood of dissociation and cardiovascular effects compared with high-dose ketamine.
“A synergistic approach lets us activate the therapeutic pathway without resorting to doses that cause side effects,” said Dr. Liston.
What sustains the antidepressant benefit
A second study, published in Science Advances from the Levitz and Francis Lee laboratories, focused on mechanisms that sustain ketamine’s antidepressant effects. The researchers found that long-term benefit depends on coordinated signaling between TrkB—a receptor tyrosine kinase activated by brain-derived neurotrophic factor (BDNF)—and the G protein–coupled receptor mGluR5.
BDNF stimulates TrkB signaling, which enhances mGluR5’s contribution to synaptic potentiation (signaling cross-talk). Conversely, TrkB activation drives endocytosis of mGluR5 from the cell surface (trafficking cross-talk), limiting the receptor’s ability to promote synaptic weakening. Together, these interactions strengthen synapses that had been weakened by stress and reduce mechanisms that would later weaken them again, promoting both rapid and sustained antidepressant effects.
The study also found that compounds that positively modulate mGluR5 can amplify this TrkB/mGluR5 cross-talk and enhance ketamine’s actions, suggesting opportunities for combination therapies that sustain benefits with lower ketamine exposure.
From bench to bedside
Because the preclinical studies used existing drugs with established human safety profiles, the teams are preparing clinical trials to test whether low-dose drug combinations can reproduce ketamine’s antidepressant effects in patients without the same side effect burden. Dr. Lee and Dr. Levitz are also exploring whether combining low doses of mGluR5-targeting compounds with reduced ketamine doses can provide durable relief with fewer adverse effects.
This mechanistic research aims to replace trial-and-error prescribing with evidence-based combinations that precisely target the receptors and cell types responsible for therapeutic benefit.
“Together, these studies reshape our understanding of how ketamine helps patients,” said Dr. Lee. “They offer a clearer path to safer, rapid-acting therapies and help clinicians explain the biological basis of these treatments.”
Key Questions Answered
A: No. Ketamine is primarily an NMDA receptor antagonist, but these studies show it leverages the opioid receptor pathway—specifically mu-opioid receptors on interneurons—as a key intermediary to produce its antidepressant effects. This helps explain why blocking opioid receptors can reduce ketamine’s benefit.
A: The goal of reverse engineering is to separate therapeutic mechanisms from those that cause hallucinations or addiction. By targeting the healing receptors with much lower doses and using synergistic combinations, scientists aim to eliminate the dissociative and addictive effects associated with high-dose ketamine.
A: The short duration likely reflects whether the downstream receptor interactions that stabilize synapses—particularly TrkB/mGluR5 cross-talk—are sufficiently engaged. If that “handshake” is weak, the initial cortical reawakening won’t translate into long-term synaptic strengthening. The new research suggests supplemental drugs can help “lock in” those changes.
Editorial Notes
- This article was edited for clarity by a Neuroscience News editor.
- The journal papers were reviewed in full by the editorial team.
- Additional context was provided by staff to aid reader understanding.
About this research
Author: Krystle Lopez
Source: Weill Cornell Medicine
Contact: Krystle Lopez – Weill Cornell Medicine
Image: The image is credited to Neuroscience News
Original research: Two open-access studies underpin these findings. One study in Cell identifies GPCR targets enriched in somatostatin interneurons and demonstrates that synergistic targeting of multiple GPCRs can produce rapid antidepressant-like effects with reduced side effects. The second study in Science Advances describes TrkB/mGluR5 cross-talk as a synaptic metaplasticity mechanism that sustains ketamine’s benefits.
Research abstracts (summarized)
Mechanism-guided identification of antidepressant G protein-coupled receptor drug targets
Depression arises from dysfunction in discrete neural circuits. By tracing how ketamine produces fast antidepressant effects, researchers identified mu-opioid receptors enriched in somatostatin-expressing interneurons of the medial prefrontal cortex as key mediators. Chronic stress causes hypertrophy and overactivity of these interneurons, suppressing pyramidal neurons; ketamine rescues this imbalance. RNA sequencing revealed interneuron-enriched GPCRs, and targeting multiple GPCRs synergistically produced antidepressant-like responses while minimizing side effects, suggesting a general strategy for identifying therapeutic GPCR targets in brain disorders.
TrkB/mGluR5 cross-talk underlies a synaptic metaplasticity mechanism of ketamine
Neuromodulatory receptors coordinate forms of synaptic plasticity that underlie behavioral state changes, but how they interact has been unclear. These studies show the antidepressant action of ketamine depends on both TrkB and mGluR5. mGluR5 amplifies BDNF-driven TrkB signaling to enable synaptic potentiation, while TrkB activation promotes mGluR5 endocytosis, reducing synaptic depression. Ketamine enhances these cross-talk modes and increases surface and postsynaptic TrkB, and mGluR5 positive modulators can further boost this receptor interplay to enhance therapeutic outcomes.