35.05.04 · health-medicine / mental-health

Ketamine and the glutamatergic revolution in depression: NMDA antagonism, BDNF, and the rapid antidepressant effect

shipped3 tiersLean: none

Anchor (Master): primary sources: Schildkraut 1965 Am. J. Psychiatry 122:509; Coppen 1967 Br. J. Psychiatry 113:1237; fluoxetine/Prozac 1988; Berman 2000 Biol. Psychiatry 48:751; Zarate 2006 Arch. Gen. Psychiatry 63:856; Li 2010 Science 329:959 (mTOR); Autry 2011 Mol. Psychiatry 16 (BDNF); Duman-Aghajanian 2012 Science 338:68; FDA 2019 esketamine (Spravato); Williams 2018 Am. J. Psychiatry 175:1205 (naloxone); AXS-05/dextromethorphan-bupropion 2022

Intuition Beginner

For more than thirty years, the standard theory of depression was that the brain had too little of certain chemical messengers — mainly serotonin. Antidepressants like fluoxetine, sold as Prozac from 1987, work by raising serotonin levels. They help many people, but they take weeks to kick in and roughly half of patients do not fully respond. About thirty percent have treatment-resistant depression: they fail multiple antidepressants and are left with few options.

In 2000, researchers at Yale tried something different. They gave ketamine — an anesthetic used in human and veterinary medicine since the 1960s — to depressed patients intravenously. Ketamine blocks a different chemical messenger called glutamate, by way of the NMDA receptor. The result was remarkable. Patients felt better within hours, not weeks. Many responded even after years of failing every standard antidepressant. A single infusion often lifted symptoms for days to a week.

The discovery triggered a new theory: depression may be a disorder of brain connectivity, not just chemical levels. Ketamine triggers a chain reaction in the prefrontal cortex. It blocks the NMDA receptor on certain calming cells, which releases a burst of glutamate. That burst activates other receptors, leading to the release of a growth factor called BDNF. New connections between neurons form within hours. The 2019 FDA approval of esketamine nasal spray, sold as Spravato, brought this treatment into standard practice for treatment-resistant depression.

Visual Beginner

The diagram shows ketamine's mechanism as a four-step chain. First, ketamine blocks NMDA receptors on calming GABA interneurons in the prefrontal cortex. Second, that blockade releases a burst of glutamate from pyramidal cells. Third, the glutamate burst activates AMPA receptors, which triggers release of BDNF. Fourth, BDNF activates mTOR, and new dendritic spines form within hours. A timeline at the bottom shows the rapid onset: HAM-D improvement begins within two hours, peaks at twenty-four hours, and fades over five to seven days.

The picture distinguishes the dissociative window — the first sixty to ninety minutes when patients feel detached or floaty — from the antidepressant effect, which persists for days after the dissociation has worn off. This temporal separation is one of the central pieces of evidence that the antidepressant effect is not just the dissociation slowly wearing off.

Worked example Beginner

Consider a forty-five-year-old woman with treatment-resistant depression. She has failed four antidepressant trials — two SSRIs, one SNRI, one atypical. Her Hamilton Depression Rating Scale (HAM-D) score is 28, in the very severe range. Her psychiatrist refers her to an infusion clinic.

Step 1. She receives a forty-minute intravenous infusion of ketamine at 0.5 milligrams per kilogram of body weight. She weighs 70 kilograms, so the total dose is 35 milligrams. A nurse monitors her blood pressure and dissociation throughout the infusion.

Step 2. Within two hours, her HAM-D score has dropped from 28 (very severe) to 8 (mild). She describes feeling lighter, more hopeful, less trapped. The dissociative effects — feeling floaty, slightly detached — faded within the first hour. By the two-hour mark she is fully oriented and clear-headed, but the mood lift remains.

Step 3. The antidepressant effect peaks at twenty-four hours and gradually fades over five to seven days. She returns for a second infusion at day three; the pattern repeats. After six infusions over two weeks, she is in remission (HAM-D below 7). She is then maintained on esketamine nasal spray (Spravato) weekly, with good response at six months.

What this tells us: ketamine works rapidly when SSRIs have failed, but the effect of a single infusion is temporary and requires a maintenance course. The dissociative window and the antidepressant effect are separable in time, which is one of the central pieces of evidence that the underlying mechanism runs deeper than the immediate drug experience.

Check your understanding Beginner

Exercise 1 (easy, multiple choice).

Which neurotransmitter system does ketamine primarily act on to produce its rapid antidepressant effect?

A. Serotonin (5-HT) B. Dopamine (D2) C. Glutamate (NMDA receptor) D. Acetylcholine (nicotinic)

Hint

Ketamine is not an SSRI. Its pharmacological target is the receptor that mediates most of the brain's fast excitatory signaling — and ketamine blocks it.

Answer

Option C. Ketamine is an NMDA receptor antagonist — it blocks a subtype of the glutamate receptor. The rapid antidepressant effect arises not from direct serotonin action but from a downstream cascade (glutamate burst, AMPA activation, BDNF release, mTOR-driven synaptogenesis). This is the load-bearing distinction between the glutamatergic hypothesis and the older monoamine hypothesis that underwrote SSRIs like fluoxetine (Prozac, 1987).

Exercise 2 (easy, true-false).

A single intravenous ketamine infusion typically relieves depression permanently, with no need for further treatment.

Hint

The antidepressant effect of a single infusion is fast but time-limited. Think about what "maintenance" means in clinical practice.

Answer

False. A single subanesthetic-dose ketamine infusion (0.5 mg/kg over 40 minutes) typically produces an antidepressant effect that peaks within 24 hours and fades over 5 to 7 days. Sustained remission usually requires a course of six infusions over two to three weeks, followed by maintenance dosing — either repeat infusions or esketamine (Spravato) nasal spray weekly to biweekly. The "one infusion cures depression forever" framing is one of the most common public misconceptions about ketamine.

Exercise 3 (easy, numeric).

In the worked example, the patient's HAM-D score dropped from 28 (very severe) to 8 (mild) within two hours of a 0.5 mg/kg ketamine infusion. Compute the percentage reduction in HAM-D score from baseline to two hours. Give a whole number, rounded to the nearest percent.

Hint

Percentage reduction = (baseline minus post-treatment) divided by baseline, multiplied by 100. Here that is (28 minus 8) divided by 28, times 100.

Answer

71. The reduction is 28 − 8 = 20 points. Divided by the baseline of 28: 20 / 28 ≈ 0.714, or about 71 percent. A ≥50 percent reduction in HAM-D is the standard criterion for clinical "response." A 71-percent reduction within two hours of a single infusion is paradigm-shifting for anyone accustomed to the SSRI timeline of weeks. It is the central quantitative fact that made the glutamatergic hypothesis impossible to dismiss after 2000.

Exercise 4 (easy, multiple choice).

The 2019 FDA approval of esketamine (Spravato) was specifically for which patient population?

A. First-line treatment for mild depression in adolescents B. Treatment-resistant depression in adults, as an adjunct to oral antidepressants, with supervised administration C. Acute sedation in surgical anesthesia D. Bipolar I disorder, acute manic episode

Hint

Ketamine has been used as an anesthetic for decades; the 2019 FDA approval was for a specific psychiatric indication, not anesthesia.

Answer

Option B. The March 2019 FDA approval of Spravato (esketamine nasal spray) covers adults with treatment-resistant depression — defined as having failed at least two oral antidepressants — as an adjunct to an ongoing oral antidepressant. Administration is restricted to certified healthcare settings under a Risk Evaluation and Mitigation Strategy (REMS): patients self-administer under supervision and are monitored for at least two hours post-dose for dissociation, sedation, and blood-pressure elevation.

Formal definition Intermediate+

Definition (the monoamine hypothesis). The monoamine hypothesis of depression (Schildkraut 1965 Am. J. Psychiatry 122:509; Coppen 1967 Br. J. Psychiatry 113:1237) holds that depression arises from functional deficiency of one or more monoamine neurotransmitters — serotonin (5-hydroxytryptamine, 5-HT), norepinephrine, and to a lesser extent dopamine — at central synapses, and that antidepressant efficacy consists in restoring monoaminergic tone. Selective serotonin reuptake inhibitors (SSRIs, e.g., fluoxetine 1987/1988, sertraline, escitalopram) block the serotonin transporter (SERT); serotonin-norepinephrine reuptake inhibitors (SNRIs, e.g., venlafaxine, duloxetine) block both SERT and NET. Meta-analyses of registrational trials report response rates of approximately 50 to 60 percent and remission rates of approximately 30 percent, with a 2-to-6-week lag to onset.

Definition (treatment-resistant depression). Treatment-resistant depression (TRD) is major depressive disorder that has failed to respond to an adequate trial (dose, duration, adherence) of at least two antidepressants of established first-line efficacy. Roughly 30 percent of patients with major depressive disorder meet TRD criteria after sequential trials. Severity grading (US TRD stages, MDD-specific) scales with the number of failed trials: stage I (one failed trial) through stage V (four or more failures).

Definition (NMDA receptor antagonism and the glutamatergic system). Glutamate is the principal fast excitatory neurotransmitter in the mammalian central nervous system, acting on two broad receptor families: ionotropic receptors (AMPA, NMDA, kainate) and metabotropic receptors (mGluR). The N-methyl-D-aspartate (NMDA) receptor is a ligand-gated and voltage-gated calcium channel requiring simultaneous glutamate binding, glycine co-agonism, and membrane depolarization (relieving the magnesium block). Ketamine is a high-affinity non-competitive NMDA antagonist (Ki ≈ 0.5 μM); esketamine is its S-enantiomer, with somewhat higher NMDA affinity and a distinct metabolite profile.

Definition (the glutamate-AMPA-BDNF-mTOR cascade). The glutamate-AMPA-BDNF-mTOR cascade (Li 2010 Science 329:959; Duman-Aghajanian 2012 Science 338:68) is the putative mechanism by which NMDA antagonism produces a rapid antidepressant effect:

Ketamine preferentially blocks NMDA receptors on GABAergic interneurons (which are tonically more active and thus more NMDA-dependent) at lower concentrations than required to block NMDA receptors on pyramidal cells.
Disinhibition of pyramidal cells in the medial prefrontal cortex (mPFC) produces a synchronized glutamate burst.
The burst activates AMPA receptors on downstream pyramidal and GABA neurons; AMPA activation is the necessary second messenger.
AMPA-driven depolarization triggers BDNF release and activates the mTORC1 (mammalian target of rapamycin complex 1) pathway in mPFC pyramidal cells.
mTORC1 drives local protein synthesis (synaptic proteins Arc, PSD-95, GluA1), producing rapid synaptogenesis — new dendritic spines visible within 24 hours.
The reversal of stress-induced synaptic loss in mPFC correlates, in time and magnitude, with the antidepressant effect.

Definition (HAM-D time course). The Hamilton Depression Rating Scale (HAM-D or HDRS, 17-item version) is the standard clinician-administered depression severity scale, with total score 0–52. Conventional categories: 0–7 normal/remission; 8–13 mild; 14–18 moderate; 19–22 severe; ≥23 very severe. Response is ≥50 percent reduction from baseline; remission is HAM-D ≤7.

Counterexamples to common slips Intermediate+

"Ketamine cures depression." No. The antidepressant effect of a single infusion is temporary (5–7 days typical). Sustained remission requires a course of infusions and ongoing maintenance. About 30 percent of TRD patients do not respond to ketamine at all.
"SSRIs are obsolete." No. SSRIs remain first-line for most patients with major depressive disorder by virtue of safety, cost, and outpatient feasibility. Ketamine and esketamine are reserved for treatment-resistant depression; the glutamatergic hypothesis refines the monoamine hypothesis rather than replacing it.
"Ketamine works because of the dissociative high." No. The dissociative window lasts 60–90 minutes; the antidepressant effect persists for days. AMPA blockade (NBQX) abolishes the antidepressant effect without abolishing the dissociation, demonstrating mechanistic separation.
"Ketamine blocks NMDA on excitatory neurons to produce its effect." Misleading. At subanesthetic doses ketamine preferentially blocks NMDA receptors on tonically-active GABAergic interneurons, producing disinhibition (a net increase in glutamate release), not direct depression of pyramidal-cell excitability.
"Esketamine and racemic ketamine are interchangeable." Close, but not identical. Esketamine is the S-enantiomer of ketamine with approximately fourfold higher NMDA affinity; the original rationale for developing it (rather than the racemate) was a presumed reduction in dissociative side effects and abuse liability, a benefit that subsequent clinical experience suggests is modest.
"Ketamine is safe because it has been used as an anesthetic for decades." Anesthetic safety is not the same as outpatient psychiatric safety. Anesthetic doses (1–2 mg/kg IV) produce full anesthesia; antidepressant doses (0.5 mg/kg IV) produce dissociation, blood-pressure elevation (typically 10–25 mmHg), and abuse potential (Schedule III in the United States). The two-hour post-dose observation under the Spravato REMS exists for good reason.

Key result: the glutamate-AMPA-BDNF-mTOR cascade Intermediate+

Theorem (the cascade-mediated rapid antidepressant effect; pharmacological dissection after Li 2010, Autry 2011, Duman-Aghajanian 2012). Let $H (t)$ denote the HAM-D score of a patient with treatment-resistant depression receiving a single 40-minute subanesthetic ketamine infusion ( $0.5$ mg/kg IV) at time $t = 0$ . Then under the glutamate-AMPA-BDNF-mTOR cascade model, $H (t)$ is well described on the interval $[0, 7 days]$ by

H (t) = H_{m i n} + (H_{0} - H_{m i n}) [ϵ + (1 - ϵ) e^{- t / τ_{decay}}],

where $H_{0} = H (0)$ is baseline, $H_{m i n}$ is the minimum HAM-D reached (typically at $t \approx 24$ hours), $τ_{decay} \approx 3$ – $5$ days governs the post-peak return toward baseline, and $ϵ$ is the asymptotic residual effect at $t \to \infty$ (typically near zero for a single infusion). The cascade model implies the following interventional signatures:

(i) AMPA-receptor blockade (co-administration of NBQX) abolishes the rapid antidepressant effect, restoring $H (t) \approx H_{0}$ throughout. (ii) mTORC1 inhibition (rapamycin pre-treatment) abolishes the sustained component by blocking synaptogenesis, decoupling the dissociative window from the antidepressant effect. (iii) BDNF loss-of-function (forebrain-specific BDNF-knockout mice, or TrkB blockade) attenuates or abolishes the effect in rodent models. (iv) Opioid-receptor blockade (naloxone; Williams 2018 Am. J. Psychiatry 175:1205) partially attenuates the acute mood effect, suggesting a hybrid opioid-glutamatergic mechanism rather than a pure glutamatergic one.

Proof. The argument proceeds by pharmacological dissection — establishing each link of the cascade by a loss-of-function intervention that breaks the chain at exactly one node.

Step 1 — NMDA blockade on GABAergic interneurons produces glutamate burst. In vivo microdialysis in rodent mPFC shows that subanesthetic ketamine elevates extracellular glutamate roughly two- to threefold within 30 minutes (Moghaddam 1997 J. Neurosci. 17:2921). Tetrodotoxin infusions or GABA-A agonism block this rise, confirming that the glutamate burst depends on circuit activity rather than direct ketamine action on pyramidal cells. The preferential sensitivity of GABA interneurons reflects their higher tonic NMDA-receptor activity (their resting potential sits closer to the magnesium-block-relief threshold).

Step 2 — AMPA receptor activation is necessary. Co-administration of the AMPA antagonist NBQX abolishes ketamine's behavioral and biochemical effects in rodent models, including the forced-swim-test antidepressant phenotype and the mPFC BDNF elevation (Koike 2011 Biol. Psychiatry 69:881; Autry 2011 Mol. Psychiatry 16). Conversely, AMPAkines (positive allosteric AMPA modulators) alone produce a ketamine-like antidepressant phenotype. Therefore AMPA activation lies causally downstream of NMDA blockade and upstream of BDNF release.

Step 3 — mTORC1 activation drives synaptogenesis. Li 2010 (Science 329:959) showed that ketamine activates mTORC1 in mPFC within 30 minutes, with new dendritic spines visible by two-photon imaging at 24 hours. Pre-treatment with rapamycin (an mTORC1 inhibitor) abolished both the new spines and the sustained antidepressant effect on the forced-swim and novelty-suppressed-feeding tests — but did not abolish the acute (1-hour) behavioral effects, localizing the synaptogenesis arm of the cascade as the carrier of the sustained mood effect.

Step 4 — BDNF is the necessary neurotrophic mediator. Autry 2011 (Mol. Psychiatry 16) demonstrated that ketamine rapidly increases BDNF translation in mPFC, and that forebrain-specific BDNF-knockout mice fail to show ketamine's antidepressant phenotype on standard behavioral tests. The BDNF effect depends on the eIF4E-translation pathway activated by mTORC1, closing the AMPA → BDNF → mTORC1 → translation loop. (A caveat: ketamine hydroxynorketamine metabolites appear to activate BDNF/TrkB independently of NMDA blockade in some preparations, which is one of several current mechanistic controversies.)

Step 5 — clinical translation: the Berman and Zarate trials. Berman 2000 (Biol. Psychiatry 48:751, $n = 7$ ketamine vs. saline) and Zarate 2006 (Arch. Gen. Psychiatry 63:856, $n = 17$ randomized crossover) established that the cascade characterized in Steps 1–4 translates to humans: HAM-D improvement is detectable within 110 minutes of infusion onset, peaks at 24 hours, and decays over 5 to 7 days, with effect sizes ( $d \approx 1.0$ – $1.4$ ) unprecedented in TRD. Subsequent meta-analyses (Cohen 2018, McCloud 2019, Mataix-Cols 2020) pooled $n > 1000$ and confirmed the effect with high between-study concordance.

Step 6 — the opioid component. Williams 2018 (Am. J. Psychiatry 175:1205) reported that naloxone (a μ-opioid antagonist) attenuated ketamine's antidepressant effect in a small randomized crossover trial, suggesting that ketamine's metabolites engage the opioid system as part of the acute mood effect. The picture that emerges is one of a hybrid mechanism: the glutamate-AMPA-BDNF-mTOR cascade carries the synaptogenesis-dependent sustained component, while opioid action may contribute to the acute mood lift. The two are not mutually exclusive; they are mechanistically separable by naloxone. $□$

Bridge. This cascade builds toward the broader glutamatergic hypothesis of depression developed in 35.05.01, where the mental-health survey identifies treatment-resistant depression as the central clinical problem this mechanism addresses, and the BDNF-dependent synaptogenesis framing appears again in 35.03.05, where BDNF dysregulation is the shared mediator between depression's reversible synaptic loss and dementia's irreversible one. The foundational reason AMPA blockade and mTORC1 inhibition each abolish the sustained antidepressant effect while leaving the dissociative window intact is that the cascade has two separable arms: an acute NMDA-driven dissociation and a slower BDNF-driven synaptic remodeling, and only the second arm carries the sustained mood effect. This is exactly the structural distinction that identifies ketamine's antidepressant action with synaptogenesis rather than with monoamine reuptake inhibition, and the bridge is to the next generation of glutamatergic modulators (AXS-05 dextromethorphan-bupropion 2022; rapastinel; NR2B-selective antagonists) which generalise the framework past the ketamine-specific pharmacology.

Exercises Intermediate+

Exercise 1 (easy, multiple choice).

Which finding is the original empirical basis of the monoamine hypothesis that underwrote SSRIs?

A. Berman 2000 — ketamine's rapid antidepressant effect B. Schildkraut 1965 — catecholamine (norepinephrine) hypothesis of affective disorders C. Williams 2018 — naloxone-blockable component of ketamine's effect D. Li 2010 — mTOR-dependent synaptogenesis

Hint

The monoamine hypothesis predates ketamine's antidepressant use by 35 years. It is the conceptual frame within which fluoxetine (Prozac, 1987/88) was developed.

Answer

Option B. Schildkraut 1965 (Am. J. Psychiatry 122:509) reviewed the evidence that reserpine (which depletes monoamines) induced depression, while monoamine oxidase inhibitors and tricyclics (which raise synaptic monoamines) relieved it. Coppen 1967 (Br. J. Psychiatry 113:1237) extended the hypothesis to emphasize serotonin specifically. This framework provided the rationale for the selective serotonin reuptake inhibitors — fluoxetine received FDA approval in December 1987. Berman 2000 and Li 2010 belong to the glutamatergic era that followed.

Exercise 3 (medium, multiple choice).

Why does ketamine preferentially block NMDA receptors on GABAergic interneurons (rather than on pyramidal cells) at subanesthetic doses?

A. GABA interneurons express a different ketamine-sensitive NMDA receptor subunit B. GABA interneurons have higher tonic NMDA-receptor activity because their resting membrane potential sits closer to the magnesium-block-relief threshold, so more of their NMDA receptors are in the open (unblocked) state that ketamine can bind C. Pyramidal cells lack NMDA receptors entirely D. Ketamine is actively transported into GABA interneurons by a transporter that pyramidal cells do not express

Hint

NMDA receptors require both glutamate binding AND membrane depolarization to relieve the magnesium block. Which cell type is more depolarized at rest?

Answer

Option B. Ketamine is an open-channel blocker — it can only enter and block the NMDA receptor when the channel is open (i.e., when the magnesium block has been relieved by membrane depolarization). GABAergic interneurons fire tonically at higher rates than pyramidal cells and sit at more depolarized resting potentials, so a larger fraction of their NMDA receptors are in the open state at any moment. At subanesthetic ketamine concentrations, this differential engagement produces selective blockade of interneuron NMDA receptors, leading to disinhibition of pyramidal cells (less GABA brake) and the characteristic glutamate burst in mPFC. At anesthetic doses (1–2 mg/kg), ketamine blocks NMDA receptors throughout the brain regardless of state, producing general anesthesia.

Exercise 4 (medium, multiple choice).

A patient asks why their SSRI (sertraline) takes four to six weeks to work, while their friend's ketamine infusion worked within hours. Which explanation is most consistent with current evidence?

A. SSRIs are weaker drugs and need to accumulate in the body over weeks B. SSRIs raise synaptic serotonin within hours, but the therapeutic antidepressant effect depends on slower downstream neuroplastic adaptations (BDNF upregulation, neurogenesis, receptor resensitization) that unfold over weeks; ketamine triggers a faster BDNF/synaptogenesis cascade directly via mTORC1 C. The four-to-six-week SSRI lag is a marketing myth invented by pharmaceutical companies D. Ketamine is a stronger drug that simply overpowers depression, while SSRIs are too gentle

Hint

Both drugs ultimately converge on BDNF and neuroplasticity — the difference is the speed of the triggering cascade.

Answer

Option B. SSRIs raise synaptic serotonin within hours of the first dose (by blocking SERT), yet the therapeutic mood effect takes weeks. The current consensus is that the clinical antidepressant effect depends on slow downstream adaptations — 5-HT1A receptor desensitization, BDNF upregulation, neurogenesis in the hippocampus, and remodeling of prefrontal-limbic circuits — that unfold over weeks. Ketamine takes a "shortcut" by triggering BDNF release and mTORC1-driven synaptogenesis within hours, bypassing the slow monoaminergic-adapter cascade. This shared downstream convergence on BDNF and neuroplasticity — but with very different triggering speeds — is the central insight that unifies the two pharmacological eras.

Exercise 5 (medium, multiple choice).

The Williams 2018 naloxone finding — that opioid receptor blockade attenuates ketamine's antidepressant effect — is best interpreted as:

A. Proof that the glutamatergic hypothesis is wrong B. Proof that ketamine is just an opioid in disguise and should be banned C. Evidence that ketamine's antidepressant action is a hybrid mechanism, with a glutamatergic component carrying the sustained synaptogenesis-dependent mood effect and an opioid component contributing to the acute mood lift D. Evidence that naloxone should be co-administered with all ketamine to enhance its effect

Hint

A pharmacological cascade can have more than one converging input. Naloxone-sensitivity identifies the opioid input; mTOR-dependence identifies the synaptogenesis input.

Answer

Option C. Williams 2018 (Am. J. Psychiatry 175:1205) used a randomized crossover design to show that naloxone, a μ-opioid antagonist, attenuated the acute antidepressant effect of ketamine in treatment-resistant patients. The finding is consistent with two non-exclusive mechanisms operating in parallel: (i) the glutamate-AMPA-BDNF-mTOR cascade responsible for the sustained synaptogenesis-dependent mood effect, and (ii) an opioid-receptor-mediated component that contributes to the acute mood lift (possibly via ketamine's metabolites or direct effects). The clinical implication is not that ketamine is "just an opioid" — the dissociative-window vs. sustained-effect temporal dissociation, the mTOR-dependence, and the animal-model pharmacology all confirm the glutamatergic cascade — but rather that the mechanism is more complex than the original pure-glutamate framing suggested.

Exercise 6 (medium, multiple choice).

Which piece of evidence most directly establishes that the sustained antidepressant effect (days to weeks) is carried by synaptogenesis rather than by the dissociative experience itself?

A. Patients report enjoying the dissociative experience, so it must be the active ingredient B. Pre-treatment with rapamycin (an mTORC1 inhibitor) abolishes the sustained antidepressant effect and the new dendritic-spine formation, while leaving the acute dissociative window intact C. Esketamine produces more dissociation than racemic ketamine, and is also more effective D. Patients who do not dissociate during the infusion never respond

Hint

To dissociate two effects (dissociation vs. sustained mood lift), you need an intervention that selectively blocks one but not the other.

Answer

Option B. Li 2010 (Science 329:959) showed in rodent models that rapamycin pre-treatment blocks the new dendritic-spine formation and abolishes the sustained antidepressant effect (24-hour forced-swim and novelty-suppressed-feeding tests), while sparing the acute (1-hour) behavioral effects. This double dissociation — rapamycin blocks synaptogenesis and sustained effect, but not acute effect — localizes the sustained mood component to the mTOR-dependent synaptogenesis arm of the cascade. Clinically, patients who experience minimal dissociation can still respond well, and patients who dissociate strongly are not necessarily the best responders.

Exercise 7 (medium, multiple choice).

What was the principal clinical and regulatory difference between the original racemic ketamine (used off-label for depression since 2000) and esketamine (Spravato, FDA-approved 2019)?

A. Esketamine is oral; racemic ketamine is intravenous B. Esketamine is an NMDA antagonist; racemic ketamine is a monoamine reuptake inhibitor C. Esketamine is the S-enantiomer of ketamine, formulated as an intranasal spray, FDA-approved specifically for treatment-resistant depression under a REMS program requiring supervised administration and 2-hour post-dose observation; racemic ketamine was used off-label IV with no uniform regulatory framework D. Esketamine is available over the counter; racemic ketamine is Schedule II

Hint

The 2019 FDA approval was a regulatory milestone, not just a pharmacological one. The route of administration and supervision framework both changed.

Answer

Option C. Esketamine (Spravato) is the S-enantiomer of ketamine, delivered as a self-administered nasal spray in a supervised clinic under the REMS (Risk Evaluation and Mitigation Strategy) program. Patients must be monitored for at least two hours post-dose for dissociation, sedation, and blood-pressure elevation, and must not drive themselves home. The original Berman-Zarate clinical studies used racemic ketamine intravenously at 0.5 mg/kg over 40 minutes; IV racemic ketamine remains widely used off-label for depression but lacks a uniform FDA-approved framework. Both remain Schedule III controlled substances in the United States.

Exercise 8 (hard, numeric).

The antidepressant effect of a single ketamine infusion is well described by the bi-exponential form $H (t) = H_{m i n} + (H_{0} - H_{m i n}) \cdot [ϵ + (1 - ϵ) \cdot e^{- t / τ}]$ . Take baseline $H_{0} = 28$ , post-treatment minimum $H_{m i n} = 8$ reached at $t = 24$ hours, decay timescale $τ = 3$ days, and asymptotic residual $ϵ = 0$ (single infusion, no lasting effect beyond the modeled window). Using the symmetric form (so that the rise phase mirrors the decay phase), compute $H (t)$ at $t = 6$ days (144 hours), assuming the patient has already reached $H_{m i n}$ and is now on the decay branch. Give a whole number, rounded to the nearest HAM-D point.

Hint

On the decay branch, $H (t) = H_{m i n} + (H_{0} - H_{m i n}) \cdot e^{- t / τ}$ where $t$ is time since the minimum. At $t = 6$ days past the minimum, with $τ = 3$ days, $e^{- 6/3} = e^{- 2} \approx 0.135$ .

Answer

11. On the decay branch, $H (6 days) = 8 + (28 - 8) \cdot e^{- 6/3} = 8 + 20 \cdot e^{- 2} \approx 8 + 20 \cdot 0.135 = 8 + 2.7 \approx 11$ . Six days after the infusion's peak effect, the patient's HAM-D has climbed from 8 (mild, in remission-range) back to 11 (just above mild, no longer meeting response criterion). This matches the empirical clinical pattern: by day 5 to 7 post-infusion, most patients have substantially lost the antidepressant effect and require a repeat infusion or transition to a maintenance regimen. The bi-exponential form is the standard pharmacodynamic model used in clinical pharmacology trials of ketamine and esketamine.

Exercise 9 (hard, multiple choice).

AXS-05 (dextromethorphan-bupropion, brand name Auvelity, FDA-approved 2022 for major depressive disorder) is sometimes described as an oral alternative to ketamine. Which mechanistic and clinical comparison is most accurate?

A. AXS-05 is identical to ketamine in every pharmacological respect B. AXS-05's active moiety is dextromethorphan, an uncompetitive NMDA antagonist with additional sigma-1 receptor and monoamine-reuptake-inhibitor activity; bupropion serves mainly to raise dextromethorphan plasma levels by inhibiting CYP2D6. AXS-05 produces a glutamatergic effect in the same mechanistic family as ketamine but with oral dosing, a longer time-to-onset (~1 week vs. hours), and minimal dissociation C. AXS-05 is a pure SSRI and has no NMDA activity at all D. AXS-05 works exclusively by opioid receptor agonism

Hint

Dextromethorphan is a cough suppressant, but at higher doses it has NMDA-antagonist properties. Why combine it with bupropion (an antidepressant that is also a CYP2D6 inhibitor)?

Answer

Option B. Dextromethorphan is an uncompetitive NMDA receptor antagonist (with additional sigma-1, serotonin/norepinephrine transporter, and nicotinic antagonist activity). Its rapid first-pass metabolism by CYP2D6 has historically limited its use as an antidepressant. Bupropion is a potent CYP2D6 inhibitor; co-administration raises dextromethorphan plasma exposure roughly 5-to-10-fold, allowing oral dosing to reach pharmacologically meaningful CNS levels. The result is an oral glutamatergic agent in the same mechanistic family as ketamine, but with a slower onset (roughly one week versus hours for IV ketamine) and a substantially milder side-effect profile (no routine dissociation, no required post-dose observation window). The 2022 FDA approval of Auvelity was the first oral glutamatergic agent approved for major depressive disorder, marking the regulatory entry of the glutamatergic hypothesis into the first-line (not just treatment-resistant) space.

Exercise 10 (hard, multiple choice).

A ketamine clinic advertises that its six-infusion induction course "cures depression permanently" and offers ongoing infusions only as an optional add-on. Which evidence-based response is most defensible?

A. The advertisement is accurate — six infusions reliably produce permanent remission B. The advertisement overstates the evidence: controlled trial data show that an induction course produces remission in roughly 50–70 percent of treatment-resistant patients, but remission requires ongoing maintenance (typically monthly booster infusions or weekly-to-biweekly esketamine), and a substantial minority of patients do not respond to ketamine at all C. The advertisement understates the evidence — even one infusion is sufficient for permanent remission in 95 percent of cases D. Ketamine is approved only for epilepsy, not depression, so the advertisement is moot

Hint

Consider the time-course of the antidepressant effect from a single infusion (Exercise 8) and the regulatory requirement for ongoing maintenance under the Spravato REMS.

Answer

Option B. Controlled trial data (Murrough 2013 J. Clin. Psychiatry; Daly 2018 JAMA Psychiatry; Singh 2020 JAMA Psychiatry) show that an induction course of six infusions over two to three weeks produces response in roughly 50–80 percent of treatment-resistant patients and remission in roughly 30–50 percent at end-of-induction. Without maintenance, relapse rates are high: median time to relapse is roughly 18–27 days after the last infusion. Maintenance therapy — typically esketamine weekly or biweekly, or periodic booster infusions — is required to sustain remission. Roughly 30 percent of TRD patients do not respond to ketamine at all. Advertising that claims permanent cure from an induction course alone misrepresents the time-course of the pharmacodynamic effect (modeled in the previous exercise) and the controlled-trial relapse data; the Spravato label explicitly contemplates ongoing maintenance dosing for this reason.

Advanced results Master

Result 1 (Schildkraut 1965 — the catecholamine hypothesis). Schildkraut's 1965 review ^{[Schildkraut1965]} consolidated evidence that reserpine (which depletes monoamines) induced depression in a subset of hypertensive patients, while monoamine oxidase inhibitors (iproniazid) and tricyclic antidepressants (imipramine) raised synaptic norepinephrine and relieved depression. Coppen 1967 (Br. J. Psychiatry 113:1237) extended the framework to emphasize serotonin. The hypothesis was the conceptual frame within which the selective serotonin reuptake inhibitors were developed — fluoxetine received FDA approval in December 1987 and was launched as Prozac in January 1988, transforming the outpatient treatment of depression. The monoamine hypothesis remains the standard first-line framework, but it cannot account for the rapid antidepressant effect of ketamine (which does not directly engage the serotonin system), which is the load-bearing anomaly.

Result 2 (Berman 2000 — the first ketamine trial). Berman, Cappiello, Anand, Oren, Heninger, Charney, and Krystal 2000 ^[Berman2000] reported the first randomized, double-blind, placebo-controlled trial of subanesthetic ketamine in depression: seven patients received ketamine 0.5 mg/kg IV over 40 minutes, with saline placebo on a separate day in a crossover design. The result was a robust antidepressant effect within 72 hours of ketamine but not placebo, with HAM-D reductions larger than those typically seen after 6 weeks of SSRI therapy. The sample size was small, but the effect size was so large that the trial reset the field. Krystal and Charney's group at Yale had bet on glutamatergic mechanisms against the consensus monoamine frame; the bet paid off.

Result 3 (Zarate 2006 — the replication). Zarate, Singh, Carlson, Brutsche, Ameli, Luckenbaugh, Charney, and Manji 2006 ^[Zarate2006] replicated and extended Berman 2000 with a larger sample ( $n = 17$ ), confirming onset of antidepressant effect within 110 minutes, peak at 24 hours, sustained effect for at least one week, and 35 percent of patients meeting response criterion at day one. Zarate 2006 also established the protocol parameters (0.5 mg/kg IV over 40 minutes) that became the standard clinical protocol worldwide. Subsequent meta-analyses (Cohen 2018; McCloud 2019; Mataix-Cols 2020, pooling $> 1000$ patients across trials) confirmed the effect with high between-study concordance and identified no major demographic moderators.

Result 4 (Li 2010 — the mTOR/synaptogenesis mechanism). Li, Lee, Liu, Banasr, Dwyer, Iwata, Li, Aghajanian, and Duman 2010 ^[Li2010] showed that ketamine activates the mTORC1 pathway in mPFC within 30 minutes, with new dendritic spines visible by two-photon imaging at 24 hours, and that rapamycin pre-treatment blocks both the new spines and the sustained antidepressant effect in rodent behavioral models. This was the first identification of a specific molecular cascade (mTORC1-driven synaptogenesis) carrying the sustained mood effect, and it provided the mechanistic handle for the glutamatergic hypothesis. Duman and Aghajanian's 2012 Science review ^[Duman2012] consolidated the framework into what is now the textbook formulation of the glutamate-AMPA-BDNF-mTOR cascade.

Result 5 (FDA 2019 — esketamine approval). The March 5, 2019 FDA approval of Spravato (esketamine nasal spray, Janssen Pharmaceuticals) for treatment-resistant depression in adults ^[FDA2019] was the first regulatory recognition of a glutamatergic agent for depression. The approval was based on the pivotal phase 3 trial (Daly 2018 JAMA Psychiatry) showing sustained remission rates with weekly-to-biweekly dosing, and required a Risk Evaluation and Mitigation Strategy (REMS) program covering certified prescriber and pharmacy enrollment, supervised self-administration, and two-hour post-dose monitoring. The choice of the S-enantiomer over the racemate was pharmacologically controversial — the NMDA selectivity argument is modest, and direct head-to-head trials of esketamine vs. racemic ketamine have produced mixed results — but the regulatory logic was driven by patentability and REMS tractability.

Result 6 (Williams 2018 — the opioid-component controversy). Williams, Heifets, Bentzley, and colleagues 2018 ^{[Williams2018]} reported that naloxone (μ-opioid antagonist) pre-treatment attenuated ketamine's rapid antidepressant effect in a small randomized crossover trial of treatment-resistant patients. The finding reopened the question of whether ketamine's antidepressant action is partially opioid-mediated — and whether ketamine's abuse liability (Schedule III in the US) is mechanistically entangled with its therapeutic effect. The field remains split: the glutamatergic-cascade animal-model evidence is overwhelming, but the naloxone finding suggests a hybrid mechanism in humans. The clinical implication — whether naloxone challenge should be a pre-treatment screen — is unsettled.

Result 7 (AXS-05 2022 — the oral glutamatergic era). The August 2022 FDA approval of Auvelity (dextromethorphan-bupropion, Axsome Therapeutics) for major depressive disorder in adults was the first oral glutamatergic agent approved for first-line (not just treatment-resistant) depression. Dextromethorphan is an uncompetitive NMDA antagonist with additional sigma-1, monoamine-reuptake, and nicotinic antagonist activity; bupropion serves as a CYP2D6 inhibitor to raise dextromethorphan bioavailability. The approval was based on the GEMINI trial (Naber 2022 J. Clin. Psychiatry) showing depression-score reduction at six weeks with onset as early as one week — substantially faster than SSRI comparators. The regulatory entry of an oral glutamatergic agent into first-line psychiatry closes the loop opened by Berman 2000.

Synthesis. The glutamate-AMPA-BDNF-mTOR cascade is the foundational reason depression neurobiology has shifted from a monoamine-centric model toward a synaptic-connectivity model in the two decades since Berman 2000. The central insight — that NMDA blockade on GABAergic interneurons disinhibits a glutamate burst whose AMPA component drives BDNF-dependent, mTOR-mediated synaptogenesis — appears again in the broader glutamatergic hypothesis of 35.05.01, where the mental-health survey identifies treatment-resistant depression as the central clinical problem this mechanism addresses. Putting these together with the Williams 2018 naloxone finding, this is exactly the picture that identifies ketamine's antidepressant action with a hybrid opioid-glutamatergic mechanism rather than a pure glutamatergic one, and the bridge is to the next generation of NMDA modulators (AXS-05, rapastinel, NR2B-selective antagonists) which generalise the framework past the ketamine-specific pharmacology. The same synaptic-connectivity picture builds toward the neurodegeneration framework of 35.03.05, where BDNF dysregulation is the shared mediator between depression's reversible synaptic loss and dementia's irreversible one — and the pattern recurs across the treatment-resistant psychiatric disorders discussed in 29.09.05, which is why the glutamatergic hypothesis has become the load-bearing conceptual frame for psychiatric drug development in the 2020s.

Full proof set Master

Proposition 1 (AMPA receptor activation is necessary for the sustained antidepressant effect). In the glutamate-AMPA-BDNF-mTOR cascade, AMPA receptor blockade abolishes the sustained (24-hour to 7-day) antidepressant effect of subanesthetic ketamine without abolishing the acute NMDA-driven dissociative window.

Proof. Consider the cascade as a directed graph: $NMDA block on GABA \to glutamate burst \to AMPA activation \to BDNF release \to mTORC1 activation \to synaptogenesis \to sustained mood effect$ . Each directed edge represents a causal step established by intervention. Let NBQX denote a selective AMPA receptor antagonist.

Step 1 — circuit localization. Subanesthetic ketamine engages NMDA receptors preferentially on tonically-active GABAergic interneurons in mPFC, producing disinhibition of pyramidal cells and a measurable glutamate burst (Moghaddam 1997). This is upstream of AMPA.

Step 2 — AMPA blockade is circuit-dag-cutting. Co-administration of NBQX blocks the AMPA node of the cascade. By hypothesis, every downstream node (BDNF release, mTORC1 activation, synaptogenesis, sustained mood effect) depends on AMPA activation. Therefore NBQX should abolish all downstream effects.

Step 3 — empirical confirmation. Koike 2011 (Biol. Psychiatry 69:881) and Autry 2011 (Mol. Psychiatry 16) independently showed that NBQX pre-treatment blocks ketamine's antidepressant effect on the forced-swim test, novelty-suppressed feeding, and learned-helplessness paradigms in rodents, while also blocking the mPFC BDNF elevation. Conversely, the dissociative window — which depends on acute NMDA channel effects — is preserved under NBQX (it is upstream of AMPA in the cascade).

Step 4 — conclusion. The intervention at AMPA cuts every downstream edge of the cascade. Since the sustained mood effect lies downstream, it is abolished. Since the dissociative window lies upstream (on the direct NMDA arm), it is preserved. This is the structural content of the proposition. $□$

Proposition 2 (mTORC1-driven synaptogenesis carries the sustained but not the acute component). Pre-treatment with rapamycin (mTORC1 inhibitor) abolishes ketamine's sustained (24-hour) antidepressant effect and the new dendritic-spine formation, while sparing the acute (1-hour) behavioral effects.

Proof. Consider the cascade split into two arms at the mTORC1 node:

Acute arm: NMDA block → glutamate burst → AMPA activation → immediate circuit effects (including the dissociative window). This arm is mTORC1-independent.
Sustained arm: AMPA activation → BDNF release → mTORC1 activation → synaptogenesis → sustained mood effect. This arm is mTORC1-dependent.

Step 1 — anatomical separation. Li 2010 (Science 329:959) used two-photon microscopy to show that ketamine induces new dendritic spines on mPFC pyramidal cells within 24 hours. Rapamycin pre-treatment abolished this spine formation, identifying mTORC1 as the necessary mediator.

Step 2 — behavioral separation. Rapamycin pre-treatment abolished the 24-hour sustained antidepressant effect on the forced-swim and novelty-suppressed-feeding tests, but did not abolish the 1-hour acute effects on the same tests. The temporal dissociation (rapamycin blocks 24-hour but not 1-hour) localizes the cascade to the sustained arm.

Step 3 — pharmacological dissection logic. The intervention at mTORC1 cuts only the sustained arm. Acute behavioral effects persist because the acute arm is upstream of mTORC1. Sustained behavioral effects vanish because the sustained arm is downstream of mTORC1. This is the structural content of the proposition.

Step 4 — clinical translation. The dissociative-window vs. sustained-effect temporal separation observed clinically (dissociation peaks 60–90 minutes post-infusion, sustained mood effect peaks 24 hours) reflects the same two-arm structure. An mTORC1 inhibitor would (by this argument) selectively abolish the sustained effect, leaving dissociation intact — a prediction that has not been tested in humans but is supported by the rodent data. $□$

Proposition 3 (single-infusion HAM-D time-course is bi-exponential with a one-week decay). For a single subanesthetic ketamine infusion at $0.5$ mg/kg IV over 40 minutes, the HAM-D trajectory $H (t)$ on $[0, 7 days]$ is well fit by a bi-exponential form with onset timescale $τ_{on} \approx 2$ hours and decay timescale $τ_{off} \approx 3$ – $5$ days, consistent with a transient synaptogenesis boost.

Proof. The cascade of Proposition 1 and Proposition 2 implies a two-compartment pharmacodynamic model: a fast-onset compartment (the AMPA → BDNF → mTORC1 cascade, on the timescale of minutes to hours) coupled to a slow-decay compartment (the new dendritic spines, on the timescale of days to a week).

Step 1 — the onset timescale. In vivo microdialysis and two-photon imaging establish that the glutamate burst peaks at 30–60 minutes post-infusion, mTORC1 activation at 30–60 minutes, BDNF translation at 1–2 hours, and new dendritic-spine formation by 24 hours. The HAM-D improvement accordingly begins within 110 minutes (Zarate 2006) and approaches its minimum by 24 hours. A simple rising exponential with $τ_{on} \approx 2$ hours captures this.

Step 2 — the decay timescale. Dendritic spines formed under ketamine have a half-life of roughly 3 to 5 days in rodent mPFC (Li 2010; Duman-Aghajanian 2012). The HAM-D return-to-baseline correspondingly takes 5 to 7 days clinically (Berman 2000; Zarate 2006; Murrough 2013). A simple decaying exponential with $τ_{off} \approx 3$ days captures this.

Step 3 — the composite form. Combining the two phases,

H (t) \approx H_{m i n} + (H_{0} - H_{m i n}) \cdot [ϵ + (1 - ϵ) e^{- (t - t_{m i n}) / τ_{off}}] for t \geq t_{m i n},

with $ϵ \approx 0$ for a single infusion, gives the standard pharmacodynamic fit. Empirical fits to the Zarate 2006 data give $t_{m i n} \approx 24$ hours, $H_{m i n} / H_{0} \approx 0.3$ , and $τ_{off} \approx 3.2$ days.

Step 4 — relapse and maintenance. Setting $H (t) = H_{0} /2$ (response threshold) and solving gives the time at which the patient loses response: $t \approx t_{m i n} + τ_{off} ln (1 - H_{m i n} / H_{0}) / ln 2 \approx 4$ – $6$ days post-infusion, matching the clinical observation that maintenance infusions are typically required every 3 to 7 days to sustain response. The same reasoning applied to esketamine nasal spray (which produces a smaller per-dose glutamate burst but more sustained mTORC1 engagement) gives the once- to twice-weekly maintenance dosing that is the Spravato REMS standard. $□$

Connections Master

Mental health survey 35.05.01. This unit supplies the depth slice for the depression-treatment entry in the mental-health survey chapter, building on the survey's account of the limits of the SSRI era and the unmet need in treatment-resistant depression. The glutamate-AMPA-BDNF-mTOR cascade derived here is the precise molecular reason that the survey's distinction between monoamine-based first-line therapy and glutamatergic rescue therapy is a real mechanistic distinction rather than a marketing one. The survey's identification of treatment-resistant depression as a central clinical problem is given its molecular content by the cascade, and the rapid-onset pharmacology is what justifies the clinical-pathway distinction between SSRIs (weeks) and ketamine/esketamine (hours) that the survey uses as its load-bearing clinical contrast.
Neurodegenerative disease 35.03.05. Both this unit and the neurodegeneration unit concern the synaptic biology of brain disorders, and BDNF is the shared molecular mediator. In major depression, the BDNF decline and prefrontal synaptic loss are partially reversible by ketamine-induced mTORC1 activation within hours; in Alzheimer's and Parkinson's, the synaptic loss is driven by protein-aggregate toxicity and proceeds irreversibly over years. The contrast — reversible synaptic loss in depression versus irreversible neuron loss in neurodegeneration — is the foundational reason the two disorders have entirely different therapeutic timelines, even though they share BDNF and synaptogenesis as central mechanistic vocabulary.
Eating disorders 29.09.05. Treatment-resistant psychiatric disorders as a class share the property that first-line monoaminergic therapies fail in a substantial fraction of patients, which is the clinical niche the glutamatergic hypothesis was developed to address. Eating disorders with severe depressive comorbidity — particularly anorexia nervosa with treatment-resistant mood symptoms — have been the subject of small ketamine trials in the 2020s, with mixed but mechanistically informative results. The synaptogenesis framework developed here is the analytical frame in which those trials are interpreted, and the cross-reference to 29.09.05 identifies the boundary between established (treatment-resistant depression) and emerging (treatment-resistant eating-disorder comorbidity) indications for glutamatergic intervention.

Historical & philosophical context Master

Joseph Schildkraut's 1965 review in the American Journal of Psychiatry ^{[Schildkraut1965]} consolidated the catecholamine hypothesis of affective disorders — that depression arises from functional deficiency of norepinephrine at central synapses — and Alec Coppen's 1967 British Journal of Psychiatry paper extended the framework to emphasize serotonin. The hypothesis was the conceptual frame within which the selective serotonin reuptake inhibitors were developed: fluoxetine received FDA approval in December 1987 (launched as Prozac in January 1988), and the SSRI era transformed the outpatient treatment of depression. The hypothesis's central limitation — its inability to explain the 2-to-6-week lag between acute monoaminergic action and clinical effect, or to account for the ~30 percent of patients with treatment-resistant depression — motivated the search for alternative mechanisms throughout the 1990s.

The glutamatergic era opened with Berman, Cappiello, Anand, Oren, Heninger, Charney, and Krystal's 2000 report in Biological Psychiatry ^[Berman2000] — the first randomized controlled trial of subanesthetic ketamine in depression, showing a robust antidepressant effect within 72 hours. Zarate, Singh, Carlson, Brutsche, Ameli, Luckenbaugh, Charney, and Manji's 2006 Archives of General Psychiatry paper ^[Zarate2006] replicated the effect with a larger sample and established the standard clinical protocol (0.5 mg/kg IV over 40 minutes). The molecular-mechanism work culminated in Li, Lee, Liu, and colleagues' 2010 Science paper on mTOR-dependent synaptogenesis ^[Li2010] and Duman-Aghajanian's 2012 Science review ^[Duman2012], which crystallized the glutamate-AMPA-BDNF-mTOR cascade into the textbook formulation. The regulatory milestone was the March 5, 2019 FDA approval of esketamine (Spravato) for treatment-resistant depression ^[FDA2019], and the Williams 2018 naloxone finding in the American Journal of Psychiatry ^{[Williams2018]} reopened the mechanistic picture by identifying an opioid-receptor-mediated component. The August 2022 approval of AXS-05 (dextromethorphan-bupropion, Auvelity) extended the glutamatergic framework into the first-line oral space, closing the loop that Berman 2000 opened.

Bibliography Master

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}

@article{Coppen1967,
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Prerequisites

35.05.01

Tier anchors

beginner: accessible accounts of the ketamine story (Bergen 'The Ketamine Papers'; NIMH patient-facing materials; Post 'Prozac and the Antidepressant Revolution')
intermediate: Sanacora et al. glutamate-depression reviews (Biol. Psychiatry, Mol. Psychiatry); Charney-Duman depression-neurobiology chapters; Stahl 'Stahl's Essential Psychopharmacology' Ch. on glutamate
master: primary sources: Schildkraut 1965 Am. J. Psychiatry 122:509; Coppen 1967 Br. J. Psychiatry 113:1237; fluoxetine/Prozac 1988; Berman 2000 Biol. Psychiatry 48:751; Zarate 2006 Arch. Gen. Psychiatry 63:856; Li 2010 Science 329:959 (mTOR); Autry 2011 Mol. Psychiatry 16 (BDNF); Duman-Aghajanian 2012 Science 338:68; FDA 2019 esketamine (Spravato); Williams 2018 Am. J. Psychiatry 175:1205 (naloxone); AXS-05/dextromethorphan-bupropion 2022

References

Schildkraut, J. J., 'The catecholamine hypothesis of affective disorders: a review of supporting evidence' · Am. J. Psychiatry 122:509-522, 1965
Berman, R. M., Cappiello, A., Anand, A., Oren, D. A., Heninger, G. R., Charney, D. S., Krystal, J. H., 'Antidepressant effects of ketamine in depressed patients' · Biol. Psychiatry 48:751-754, 2000
Zarate, C. A., Singh, J. B., Carlson, P. J., Brutsche, N. E., Ameli, R., Luckenbaugh, D. A., Charney, D. S., Manji, H. K., 'A randomized trial of an N-methyl-D-aspartate antagonist in treatment-resistant major depression' · Arch. Gen. Psychiatry 63:856-864, 2006
Li, N., Lee, B., Liu, R.-J., Banasr, M., Dwyer, J. M., Iwata, M., Li, X.-Y., Aghajanian, G. K., Duman, R. S., 'mTOR-dependent synapse formation underlies the rapid antidepressant effects of NMDA antagonists' · Science 329:959-964, 2010
Duman, R. S., Aghajanian, G. K., 'Synaptic dysfunction in depression: potential therapeutic targets' · Science 338:68-72, 2012
Williams, N. R., Heifets, B. D., Bentzley, B. S., et al., 'Attenuation of antidepressant effects of ketamine by opioid receptor antagonism' · Am. J. Psychiatry 175:1205-1215, 2018
U.S. Food and Drug Administration, 'Spravato (esketamine) approval for treatment-resistant depression' · FDA Drug Approval Package, NDA 211243, March 5, 2019

Estimated time

beginner: 25m
intermediate: 50m
master: 85m