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NMDA receptor blockade at rest triggers rapid behavioural antidepressant responses

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Clinical studies consistently demonstrate that a single sub-psychomimetic dose of ketamine, an ionotropic glutamatergic NMDAR (N-methyl-D-aspartate receptor) antagonist, produces fast-acting antidepressant responses in patients suffering from major depressive disorder, although the underlying mechanism is unclear1, 2, 3. Depressed patients report the alleviation of major depressive disorder symptoms within two hours of a single, low-dose intravenous infusion of ketamine, with effects lasting up to two weeks1, 2, 3, unlike traditional antidepressants (serotonin re-uptake inhibitors), which take weeks to reach efficacy. This delay is a major drawback to current therapies for major depressive disorder and faster-acting antidepressants are needed, particularly for suicide-risk patients3. The ability of ketamine to produce rapidly acting, long-lasting antidepressant responses in depressed patients provides a unique opportunity to investigate underlying cellular mechanisms. Here we show that ketamine and other NMDAR antagonists produce fast-acting behavioural antidepressant-like effects in mouse models, and that these effects depend on the rapid synthesis of brain-derived neurotrophic factor. We find that the ketamine-mediated blockade of NMDAR at rest deactivates eukaryotic elongation factor 2 (eEF2) kinase (also called CaMKIII), resulting in reduced eEF2 phosphorylation and de-suppression of translation of brain-derived neurotrophic factor. Furthermore, we find that inhibitors of eEF2 kinase induce fast-acting behavioural antidepressant-like effects. Our findings indicate that the regulation of protein synthesis by spontaneous neurotransmission may serve as a viable therapeutic target for the development of fast-acting antidepressants.

Figures at a glance

  1. Figure 1: Time course of NMDAR antagonist-mediated antidepressant-like behavioural effects.

    Mean immobility±s.e.m. of C57BL/6 mice in FST after acute treatment with ketamine, CPP or MK-801. Independent groups of mice were used at each time point and for each drug treatment, to avoid behavioural habituation. Analysis of variance (ANOVA) F(3,27) = 30.31, P<0.0001 for treatment groups; F(3,27) = 19.06, P<0.0001 for duration of response; F(9,81) = 9.32, P<0.0001 for treatment-duration interaction. Therefore, we examined treatment effects by time point. a, Ketamine (3.0mgkg−1) significantly reduced immobility, indicating an antidepressant-like response, at 30min, 3h, 24h and 1week, compared to vehicle treatment. b, CPP (0.5mgkg−1) significantly reduced immobility at 30min, 3h and 24h, compared to vehicle treatment. c, MK-801 (0.1mgkg−1) produced significant decreases in immobility at 30min and 3h compared to vehicle treatment. n = 10 mice per group per time point; *, P<0.05. Here and in all figures, error bars represent s.e.m.

  2. Figure 2: BDNF translation in the antidepressant effects of NMDAR antagonists.

    a, Immobility in FST after acute treatment with ketamine (3.0mgkg−1). At 30min, ANOVA F(1,35) = 17.13, P = 0.0002 for drug; F(1,35) = 7.57, P = 0.0093 for genotype–drug interaction; multiple comparisons with t-test, *, P<0.05. At 24h, in a separate cohort, ANOVA F(1,29) = 3.77, P = 0.0619 for treatment; multiple comparisons with t-test, *, P<0.05. n = 7–12 mice per group. b, Densitometric analysis of BDNF (normalized to GAPDH) in the hippocampus after treatment with vehicle (control), ketamine (3.0mgkg−1) or MK-801 (0.1mgkg−1). At 30min, ANOVA F(2,12) = 6.77, P = 0.0108 for treatment, Bonferroni post hoc test, *, P<0.05. At 24h, no significant differences were seen (n = 5–6 per group). c, Protocol for experiments using the blockers anisomycin and actinomycin D. d, Immobility at 30min after anisomycin treatment. ANOVA F(1,34) = 11.83, P = 0.0016 for treatment and F(1,34) = 10.91, P = 0.0023 for treatment–inhibitor interaction; multiple comparisons, *, P<0.05 (n = 8–10 per group). e, Immobility at 24h after anisomycin treatment. ANOVA F(1,31) = 9.34, P = 0.0046 for treatment; multiple comparisons, *, P<0.05 (n = 8–10 per group). f, Immobility of wild-type mice given vehicle or NMDA (75mgkg−1), tested 30min later in FST. g, Immobility of mice given NBQX (10mgkg−1) or picrotoxin (1mgkg−1), tested 30min later in FST. h, Immobility of mice given vehicle, ketamine (3.0mgkg−1) or ketamine+NBQX (10mgkg−1) and tested 30min later in FST. ANOVA F(2,26) = 8.226, P<0.0019; Bonferroni post hoc analysis shows that the ketamine effect is reversed by NBQX, *, P<0.05. i, Densitometric analysis of phosphorylated mTOR (normalized to mTOR) in the hippocampus 30min after treatment with vehicle or ketamine.

  3. Figure 3: Ketamine blocks NMDAR spontaneous activity, reduces the level of eEF2 phosphorylation and strengthens synaptic responses.

    a, Representative western blots showing eEF2 phosphorylation (p-eEF2) in hippocampal primary cultures. Ket, ketamine; TTX, tetrodotoxin. b, Densitometric analysis of p-eEF2 normalized to total eEF2 (left panel). Data are expressed as mean percentage±s.e.m. Tetrodotoxin alone does not alter p-eEF2, whereas AP5 or ketamine, with or without tetrodotoxin, significantly reduce the level of p-eEF2, as assessed by t-test (*, P<0.05). Right panel: application of 1μM, 5μM or 50μM ketamine causes dose-dependent decreases in p-eEF2, as assessed by t-test (*, P<0.05). c, Representative traces of NMDAR spontaneous activity after application of 1μM, 5μM or 50μM ketamine. d, Quantification of charge transfer (10s) reveals significant effects, as assessed by t-test, for all ketamine concentrations compared to controls (n = 6–16; *, P<0.05). e, Field-potential (FP) slopes are plotted as a function of time. Representative field-potential traces (average 2min) are shown during baseline (1) and at 45min (2). The asterisk refers to significantly different field-potential values (*, P<0.05). For statistical analysis, we used two-way repeated ANOVA with Bonferroni post hoc analysis. The drug–time interaction was significant (F(143,1430) = 6.723, P<0.001).

  4. Figure 4: Rapid antidepressant-like behaviour is mediated by decreased p-eEF2 and increased BDNF translation.

    a, Images of CA1 pyramidal and stratum radiatum layers after acute treatment with vehicle, ketamine or MK-801. Scale bar, 100μm; red, p-eEF2; blue, DAPI. b, Magnification of stratum radiatum; scale bar, 20μm. c, ImageJ analysis of average fluorescence intensity (a.u., arbitrary units). ANOVA on cell layer, F(2,23) = 13.13, P = 0.0002 for treatment; ANOVA on dendrites, F(2,23) = 14.06, P = 0.0001 for treatment (n = 4 per group; *, P<0.05). d, Densitometric analysis of p-eEF2 normalized to total eEF2 in the hippocampus after treatment with NMDAR antagonists. ANOVA F(2,23) = 3.183, P = 0.03 for treatment (n = 8 per group). eh, Densitometric analyses of BDNF and p-eEF2. Significant increases are seen in hippocampal BDNF protein levels (normalized to GAPDH) with rottlerin (5mgkg−1) versus vehicle (e), and with NH125 (5mgkg−1) versus vehicle (g) (t-tests, *, P<0.05). Significant decreases are seen in p-eEF2 (normalized to total eEF2) with rottlerin versus vehicle (f) and NH125 versus vehicle (h) (t-tests, *, P<0.05). i, Immobility in FST of wild-type mice given acute rottlerin (5mgkg−1) or NH125 (5mgkg−1). ANOVA F(3,44) = 8.13, P = 0.0002 for treatment; Bonferroni post hoc analysis shows significance with rottlerin or NH125 versus vehicle (*, P<0.05), but not with the MAPK inhibitor SL327 (10mgkg−1). j, Immobility of Bdnf-knockout mice or littermate controls given acute rottlerin (5mgkg−1) and tested 30min later in FST. ANOVA F(1,19) = 5.77, P = 0.0267 for treatment; Bonferroni post hoc analysis for rottlerin versus vehicle-treated controls (*, P<0.05; n = 5–7 per group).

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