Journal of Depression and Therapy
ISSN: 2476-1710
Current Issue
Volume No: 1 Issue No: 3
share this page

Review Article | Open Access
  • Available online freely | Peer Reviewed
  • Ketamine-Based Treatment of MDD: A Biologist’s Perspective

    Shupeng Li 1       Yingli Zhang 2     Qiang Zhou 1    

    1School of Chemical Biology and Biotechnology, Peking University Shenzhen Graduate School, Shenzhen, China

    2Kangning Hospital, Shenzhen, China


    Ketamine’s potential as a fast-acting reagent to treat MDD, especially treatment-resistant depression has caught much attention recently. Although much has been learned about the biological mechanisms underlying ketamine’s effect, there are a few critical issues remained to be resolved. This mini review will briefly discuss several controversial issues that warrant further studies, regarding the molecular, physiological, psychopharmacological, and behavioral effects of ketamine. Understand how ketamine works as an anti-depressant will open the door to better understanding of MDD and its treatment.

    Received 19 Jun 2017; Accepted 28 Jul 2017; Published 19 Aug 2017;

    Academic Editor:Addo Boafo, Royal Institute of mental health research

    Checked for plagiarism: Yes

    Review by: Single-blind

    Copyright©  2017 Shupeng Li, et al

    Creative Commons License    This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

    Competing interests

    The authors have declared that no competing interests exist.


    Shupeng Li, Yingli Zhang, Qiang Zhou (2017) Ketamine-Based Treatment of MDD: A Biologist’s Perspective. Journal of Depression and Therapy - 1(3):29-34.
    Download as RIS, BibTeX, Text (Include abstract )


    Despite current available antidepressants, major depressive disorder (MDD) presents as a major threat to public health, with a lifetime prevalence of 17% in the United States and 40-50% of patients unresponsive to treatment1. Moreover, the slow onset of therapeutic efficacy that usually takes 3 - 4 weeks is especially unhelpful for patients with suicidal ideation. Combined with treatment for resistant and accompanied comorbid anxiety disorders, a novel and rapidly acting antidepressant is highly desirable2.

    Ketamine is a low-affinity, activity-dependent, open channel blocker of NMDA subtype glutamate receptors (NMDARs). Ketamine has been shown to be effective in treating major depressive disorder (MDD), including treatment-resistant depression, with a rapid onset (on the order of hours) of efficacy and effective duration of days to weeks3, 4, 5. A few potential issues have been identified during the clinical testing of ketamine, which need to be resolved before ketamine or its derivatives/metabolites could be widely applied clinically. These improvements should come from a better understanding of biology of ketamine’s efficacy. In this review, we will discuss the proposed biological mechanisms and critical unresolved issues related to ketamine’s anti-depressant effects.

    Clinical Effects and Potential Biological Mechanisms

    After the serendipitous discovery of its antidepressant effects, ketamine has been successfully applied as a fast acting treatment of MDD in a clinical setting, especially for treatment-resistant MDD patients3, 4, 5. Its short-lasting and quick dissipating antidepressant properties requires repeated administration to keep its efficacy, while repetitive administration is severely limited by psychostimulant effects and addictive potentials6. It is in debate as whether these two side effects may be intricately connected to ketamine’s antidepressant effects7.

    A few biological mechanisms have been proposed for ketamine’s anti-depressant effect: (1) blockade of NMDARs on the GABAergic inhibitory neurons leads to reduced activation and enhanced excitation in the brain, the so called disinhibition hypothesis8; (2) blockade of NMDAR on the excitatory neurons at rest results in rapid protein synthesis of BDNF via reduced phosphorylated eEF29; (3) increased mTOR signaling and increase in dendritic spine density in the excitatory neurons10; (4) reduced GSK-3 signaling11. The above mechanisms are likely to be connected or shared, rather independent of each other.

    Critical Unresolved Questions for Moving Forward

    Although ketamine has shown huge potentials to be a major breakthrough in treating MDD, especially treatment-resistant depression, there are a few critical unresolved issues. A better understanding of these issues will not only facilitate ketamine’s approval for clinical use, but also provide important biological insights into the pathogenesis of MDD and its more effective treatment.

    Is there anything special for ketamine as NMDAR antagonist In addition to ketamine, various NMDAR antagonists have been tested for their anti-depression efficacy, all with inferior efficacy than ketamine but some with better side-effect profiles12. A few things worthy of further considerations: (1) High-trapping vs. low-trapping (see below); (2) targeting NMDARs at rest. Some recent works have suggested that ketamine’s effect is mediated via its inhibition of NMDAR at rest with physiological Mg2+ concentration. Interestingly, memantine does not target NMDARs at rest13 and also lacks anti-depressant effect14, 15. (3) Subunit selectivity required? Clinical studies have shown that the efficacy of selective GluN2B antagonist in treating MDD does not occur until 5 days after administration16, 17. The possibility that selective antagonist affects less number of NMDARs than ketamine and hence takes longer to show effect needs to be tested. A few preclinical studies of GluN2B antagonists have also demonstrated anti-depression effect, with the absence of it in the GluN2B KO mice 10, 18.

    Addictive potential: As one of the popular recreational drugs, Ketamine’s psychostimulant effects are also deemed to induce addictive behaviors19. It is still in debate as whether ketamine directly impacts the reward system (the dopaminergic projections from the ventral tegmental area (VTA) to the nucleus accumbens (NAc)), or only strengthens the associations between drug related contextual stimuli and drug intaking, which drives ketamine usage at certain conditions as a maladaptive memory. In other words, whether ketamine itself encompasses positive and negative reinforcing potency and elicits compulsive drug intake still need to be clarified20.

    Dissociative thoughts: Originally used as an anesthetic and analgesic drug due to it dissociative effects and distinct from other canonical anesthetic drugs, ketamine induces psychotropic effects ranging from dissociation to schizophrenia-like symptoms (positive, negative, and cognitive deficits)21. NMDAR antagonism is likely a trigger of the persistent psychosis since another NMDAR antagonist, PCP, also induces persistent psychosis22. Interestingly, memantine, a drug approved for treating Alzheimer's disease, did not induce dissociative thoughts or psychosis14, 15. Some studies have suggested these differences are caused by their different trapping characters, the off rate where high off rate (low trapping) was deemed to easily leave the channel as it closes and thus the channel function recovers. Ketamine showed an 86% trapping while mematine showed 50-70% trapping23. Most patients felt dissociation-like psychotomimesis at ketamine concentration of 50-100 ng/ml, well below the concentration required for antidepressant effect (150-200 ng/ml). Another low-trapping NMDAR antagonist AZD6765 did not induce dissociative symptoms but also exhibited limited anti-depressant effect24. This also applies to other NMADR antagonists tested on MDD patients25. In various preclinical animal models of depression, R-ketamine has been shown to have superior anti-depressant efficacy and longer-lasting effect than S-ketamine. More impressively, it has also been shown that R-ketamine is effective in a depression model refractory to the current medication for MDD patients 26, 27. Interestingly, it has also been shown that R-ket does not produce the undesirable psychotomimetic effects in animals28.

    Can AMPAR potentiators be an alternative and perhaps a better option? A recent study by Zanos and colleagues demonstrated that one of the main metabolites of ketamine, 6-hydroxy norketamine ((2R,6R)-HNK ), is the main mediator of ketamine’s anti-depressant effect29. Most importantly (2R,6R)-HNK is not a NMDAR antagonist, but rather an AMPAR potentiator. This raises a very important question about whether NMDAR antagonism is required for ketamine’s efficacy, and furthermore, whether AMPAR potentiator could be a better alternative due its lack of additive potential in triggering dissociative thoughts. Positive allosteric modulators that enhance AMPAR activity (such as the CX series Ampakines) has shown significant benefits in various preclinical tests30, but ultimate did not proceed in clinical trials due to potential pathological concerns.

    Is synaptic plasticity required? The fact that repetitive infusion of ketamine is required to prevent relapse of depressive symptoms suggests that no lasting changes have occurred with ketamine administration and hence unlikely plasticity is required for its efficacy. Furthermore, although preclinical studies have shown increased density of dendritic spines and increased number of AMPARs9-10, no study has demonstrated a clear increase of synaptic connections in an input-specific manner. If new connections are formed, where do the presynaptic inputs come from? Are they branching off the existing ones or converting silent synapse into functioning ones? A possible mechanism is that ketamine induces metaplasticity to alter the subsequent generation of plasticity. Preliminary report showed ketamine may exert antidepressant effects via modulation of metaplasticity31.

    What major brain regions are involved? Two likely regions are hippocampus and PFC, and it will be quite informative to compare ketamine and its metabolite, or other NMDAR antagonists, or AMPAR potentiators, to understand whether they activate distinction brain regions.

    Summary and Future Directions

    Ketamine offers a golden opportunity, to both serve as an anti-depressant drug and to our better understanding of the pathology of MDD. One of the critical questions is whether NMDAR antagonism is required for ketamine’s fast action. Once we are sure of this, the path forward is straighter.


    This work is supported by Shenzhen Municipal Science and Technology Innovation Council

    Grant No:JCYJ20150529153646078, ZDSYS201504301539161,JSGG20140703163838793.


    1.Kessler R C, Chiu W T, Demler O, Merikangas K R, Walters E E. (2005) . Prevalence, severity, and comorbidity of 12-month DSM-IV disorders in the National Comorbidity Survey Replication. Arch Gen Psychiatry 62(6), 617-27.
    2.M H Trivedi, Fava M, S R Wisniewski, M E Thase, Quitkin F et al. (2006) Medication augmentation after the failure of SSRIs for depression. , N Engl J Med 354(12), 1243-52.
    3.R M Berman, Cappiello A, Anand A, D A Oren, G R Heninger et al. (2000) Antidepressant effects of ketamine in depressed patients. Biol Psychiatry. 47(4), 351-4.
    4.R B Price, M K Nock, D S Charney, S J Mathew. (2009) Effects of intravenous ketamine on explicit and implicit measures of suicidality in treatment-resistant depression. Biol Psychiatry. 66(5), 522-6.
    5.C A Zarate, J B Singh, P J Carlson, N E Brutsche, Ameli R et al. (2006) A randomized trial of an N-methyl-D-aspartate antagonist in treatment-resistant major depression. Arch Gen Psychiatry. 63(8), 856-64.
    6.J W Murrough, A M Perez, Pillemer S, Stern J, M K Parides et al. (2013) Rapid and longer-term antidepressant effects of repeated ketamine infusions in treatment-resistant major depression. Biol Psychiatry. 74(4), 250-6.
    7.D A Luckenbaugh, M J Niciu, D F Ionescu, N M, E M Richards et al. (2014) Do the dissociative side effects of ketamine mediate its antidepressant effects?. , J Affect Disord 159, 56-61.
    8.Moghaddam B, Adams B, Verma A, Daly D. (1997) Activation of glutamatergic neurotransmission by ketamine: a novel step in the pathway from NMDA receptor blockade to dopaminergic and cognitive disruptions associated with the prefrontal cortex. , J Neurosci 17(8), 2921-7.
    9.A E, Adachi M, Nosyreva E, Na E S, Los M F et al. (2011) NMDA receptor blockade at rest triggers rapid behavioural antidepressant responses. , Nature 475(7354), 91-5.
    10.Li N, Lee B, R J Liu, Banasr M, J M Dwyer et al. (2010) mTOR-dependent synapse formation underlies the rapid antidepressant effects of NMDA antagonists. , Science 329(5994), 959-64.
    11.Beurel E, Song L, R S Jope. (2011) Inhibition of glycogen synthase kinase-3 is necessary for the rapid antidepressant effect of ketamine in mice. , Mol Psychiatry 16(11), 1068-70.
    12.M J Niciu, I D Henter, D A Luckenbaugh, C A Zarate, D S Charney. (2014) Glutamate receptor antagonists as fast-acting therapeutic alternatives for the treatment of depression: ketamine and other compounds. , Annu Rev Pharmacol Toxicol 54, 119-39.
    13.E S Gideons, E T Kavalali, L M Monteggia. (2014) Mechanisms underlying differential effectiveness of memantine and ketamine in rapid antidepressant responses. Proc Natl Acad Sci U S A 111(23), 8649-54.
    14.J M Ferguson, R N Shingleton. (2007) An open-label, flexible-dose study of memantine in major depressive disorder. Clin Neuropharmacol. 30(3), 136-44.
    15.E J Lenze, E R Skidmore, A E Begley, J W Newcomer, M A Butters et al. (2012) Memantine for late-life depression and apathy after a disabling medical event: a 12-week, double-blind placebo-controlled pilot study. , Int J Geriatr Psychiatry 27(9), 974-80.
    16.S H Preskorn, Baker B, Kolluri S, F S Menniti, Krams M et al. (2008) An innovative design to establish proof of concept of the antidepressant effects of the NR2B subunit selective N-methyl-D-aspartate antagonist, CP-101,606, in patients with treatment-refractory major depressive disorder. , J Clin Psychopharmacol 28(6), 631-7.
    17.Ibrahim L, Granados Diaz, Jolkovsky N, Brutsche L, Luckenbaugh N et al. (2012) A Randomized, placebo-controlled, crossover pilot trial of the oral selective NR2B antagonist MK-0657 in patients with treatment-resistant major depressive disorder. , J Clin Psychopharmacol 32(4), 551-7.
    18.O H Miller, Yang L, C, E A Hargroder, Zhang Y et al. (2014) GluN2B-containing NMDA receptors regulate depression-like behavior and are critical for the rapid antidepressant actions of ketamine. Elife. 3, 03581.
    19.Kamaya H, P R Krishna. (1987) Ketamine addiction. Anesthesiology. 67(5), 861-2.
    20.F W Hopf. (2017) Do specific NMDA receptor subunits act as gateways for addictive behaviors? Genes Brain Behav. 16(1), 118-138.
    21.J H Krystal, L P Karper, J P Seibyl, G K Freeman, Delaney R et al. (1994) Subanesthetic effects of the noncompetitive NMDA antagonist, ketamine, in humans. Psychotomimetic, perceptual, cognitive, and neuroendocrine responses. Arch Gen Psychiatry. 51(3), 199-214.
    22.J M Rainey, M K Crowder. (1975) Prolonged psychosis attributed to phencyclidine: report of three cases. , Am J Psychiatry 132(10), 1076-8.
    23.S E Kotermanski, J T Wood, J W.Memantine binding to a superficial site on NMDA receptors contributes to partial trapping. , J Physiol 2009, 587 (Pt 19, 4589-604.
    24.Sanacora G, M A Smith, Pathak S, H L Su, P H Boeijinga et al. (2014) Lanicemine: a low-trapping NMDA channel blocker produces sustained antidepressant efficacy with minimal psychotomimetic adverse effects. Mol Psychiatry. 19(9), 978-85.
    25.C A Zarate, Mathews D, Ibrahim L, J F Chaves, Marquardt C et al. (2013) A randomized trial of a low-trapping nonselective N-methyl-D-aspartate channel blocker in major depression. Biol Psychiatry. 74(4), 257-64.
    26.J C Zhang, S X Li, Hashimoto K. (2014) R (-)-ketamine shows greater potency and longer lasting antidepressant effects than S (+)-ketamine. Pharmacol Biochem Behav. 116-137.
    27.Fukumoto K, Toki H, Iijima M, Hashihayata T, J I Yamaguchi et al. (2017) Antidepressant Potential of (R)-Ketamine in Rodent Models: Comparison with (S)-Ketamine. , J Pharmacol Exp Ther 361(1), 9-16.
    28.Yang C, Shirayama Y, J C Zhang, Ren Q, Yao W et al. (2015) R-ketamine: a rapid-onset and sustained antidepressant without psychotomimetic side effects. Transl Psychiatry. 5, 632.
    29.Zanos P, Moaddel R, P J Morris, Georgiou P, Fischell J et al. (2016) NMDAR inhibition-independent antidepressant actions of ketamine metabolites. , Nature 533(7604), 481-6.
    30.Arai A C, Kessler M. (2007) Pharmacology of ampakine modulators: from AMPA receptors to synapses and behavior. , Curr Drug Targets 8(5), 583-602.
    31.Izumi Y, C F Zorumski. (2014) Metaplastic effects of subanesthetic ketamine on CA1 hippocampal function. Neuropharmacology. 86, 273-81.