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The physiology of N -methyl- d -aspartate (NMDA) receptors is fundamental to brain development and function. NMDA receptors are ionotropic glutamate receptors that function as heterotetramers composed mainly of GluN1 and GluN2 subunits. Activation of NMDA receptors requires binding of neurotransmitter agonists to a ligand-binding domain (LBD) and structural rearrangement of an amino-terminal domain (ATD). Recent crystal structures of GluN1–GluN2B NMDA receptors bound to agonists and an allosteric inhibitor, ifenprodil, represent the allosterically inhibited state. However, how the ATD and LBD move to activate the NMDA receptor ion channel remains unclear. Here we applied X-ray crystallography, single-particle electron cryomicroscopy and electrophysiology to rat NMDA receptors to show that, in the absence of ifenprodil, the bi-lobed structure of GluN2 ATD adopts an open conformation accompanied by rearrangement of the GluN1–GluN2 ATD heterodimeric interface, altering subunit orientation in the ATD and LBD and forming an active receptor conformation that gates the ion channel. X-ray crystallography, single-particle electron cryomicroscopy and electrophysiology were used to study the conformational changes that take place during the activation and inhibition of a mammalian GluN1b–GluN2B N -methyl- d -aspartate receptor. Conformational alterations of NMDA receptor activation NMDA ( N -methyl- D -aspartate) receptors are ionotropic glutamate receptors that are involved in brain development and function, including learning and memory formation, and dysfunctional NMDA receptors are associated with various neurological diseases and disorders. These membrane proteins are heterotetramers, comprising two copies each of the GluN1 and GluN2 subunits, which bind glycine and L -glutamate, respectively. Hiro Furukawa and colleagues use X-ray crystallography, single-particle electron cryomicroscopy and electrophysiology to study the conformational changes that take place during the activation and inhibition of rat NMDA receptors. In the absence of the allosteric inhibitor ifenprodil, the bi-lobed structure of GluN2 amino-terminal domain adopts an open conformation accompanied by rearrangement of the GluN1–GluN2 amino-terminal domain heterodimeric interface, altering subunit orientation in the ligand-binding and amino-terminal domains to form an active receptor conformation that gates the ion channel.

Ketamine is a non-competitive channel blocker of N -methyl- d -aspartate (NMDA) receptors 1 . A single sub-anaesthetic dose of ketamine produces rapid (within hours) and long-lasting antidepressant effects in patients who are resistant to other antidepressants 2 , 3 . Ketamine is a racemic mixture containing equal parts of ( R )- and ( S )-ketamine, with the ( S )-enantiomer having greater affinity for the NMDA receptor 4 . Here we describe the cryo-electron microscope structures of human GluN1–GluN2A and GluN1–GluN2B NMDA receptors in complex with S -ketamine, glycine and glutamate. Both electron density maps uncovered the binding pocket for S -ketamine in the central vestibule between the channel gate and selectivity filter. Molecular dynamics simulation showed that S -ketamine moves between two distinct locations within the binding pocket. Two amino acids—leucine 642 on GluN2A (homologous to leucine 643 on GluN2B) and asparagine 616 on GluN1—were identified as key residues that form hydrophobic and hydrogen-bond interactions with ketamine, and mutations at these residues reduced the potency of ketamine in blocking NMDA receptor channel activity. These findings show structurally how ketamine binds to and acts on human NMDA receptors, and pave the way for the future development of ketamine-based antidepressants. Structures of ketamine bound to human NMDA receptors show how ketamine inhibits receptor activity.

Astrocytes control brain activity via both metabolic processes and gliotransmission, but the physiological links between these functions are scantly known. Here we show that endogenous activation of astrocyte type-1 cannabinoid (CB1) receptors determines a shift of glycolysis towards the lactate-dependent production of D-serine, thereby gating synaptic and cognitive functions in male mice. Mutant mice lacking the CB1 receptor gene in astrocytes (GFAP-CB1-KO) are impaired in novel object recognition (NOR) memory. This phenotype is rescued by the gliotransmitter D-serine, by its precursor L-serine, and also by lactate and 3,5-DHBA, an agonist of the lactate receptor HCAR1. Such lactate-dependent effect is abolished when the astrocyte-specific phosphorylated-pathway (PP), which diverts glycolysis towards L-serine synthesis, is blocked. Consistently, lactate and 3,5-DHBA promoted the co-agonist binding site occupancy of CA1 post-synaptic NMDA receptors in hippocampal slices in a PP-dependent manner. Thus, a tight cross-talk between astrocytic energy metabolism and gliotransmission determines synaptic and cognitive processes.

Anti-NMDA receptor (NMDAR) encephalitis is an autoimmune disorder in which the use of immunotherapy and the long-term outcome have not been defined. We aimed to assess the presentation of the disease, the spectrum of symptoms, immunotherapies used, timing of improvement, and long-term outcome. In this multi-institutional observational study, we tested for the presence of NMDAR antibodies in serum or CSF samples of patients with encephalitis between Jan 1, 2007, and Jan 1, 2012. All patients who tested positive for NMDAR antibodies were included in the study; patients were assessed at symptom onset and at months 4, 8, 12, 18, and 24, by use of the modified Rankin scale (mRS). Treatment included first-line immunotherapy (steroids, intravenous immunoglobulin, plasmapheresis), second-line immunotherapy (rituximab, cyclophosphamide), and tumour removal. Predictors of outcome were determined at the Universities of Pennsylvania (PA, USA) and Barcelona (Spain) by use of a generalised linear mixed model with binary distribution. We enrolled 577 patients (median age 21 years, range 8 months to 85 years), 211 of whom were children (<18 years). Treatment effects and outcome were assessable in 501 (median follow-up 24 months, range 4–186): 472 (94%) underwent first-line immunotherapy or tumour removal, resulting in improvement within 4 weeks in 251 (53%). Of 221 patients who did not improve with first-line treatment, 125 (57%) received second-line immunotherapy that resulted in a better outcome (mRS 0–2) than those who did not (odds ratio [OR] 2·69, CI 1·24–5·80; p=0·012). During the first 24 months, 394 of 501 patients achieved a good outcome (mRS 0–2; median 6 months, IQR 2–12) and 30 died. At 24 months’ follow-up, 203 (81%) of 252 patients had good outcome. Outcomes continued to improve for up to 18 months after symptom onset. Predictors of good outcome were early treatment (0·62, 0·50–0·76; p<0·0001) and no admission to an intensive care unit (0·12, 0·06–0·22; p<0·0001). 45 patients had one or multiple relapses (representing a 12% risk within 2 years); 46 (67%) of 69 relapses were less severe than initial episodes (p<0·0001). In 177 children, predictors of good outcome and the magnitude of effect of second-line immunotherapy were similar to those of the entire cohort. Most patients with anti-NMDAR encephalitis respond to immunotherapy. Second-line immunotherapy is usually effective when first-line treatments fail. In this cohort, the recovery of some patients took up to 18 months. The Dutch Cancer Society, the National Institutes of Health, the McKnight Neuroscience of Brain Disorders award, The Fondo de Investigaciones Sanitarias, and Fundació la Marató de TV3.

Ketamine, an N -methyl- D -aspartate receptor (NMDAR) channel blocker, has been found to induce rapid and robust antidepressant-like effects in rodent models and in treatment-refractory depressed patients. However, the marked acute psychological side effects of ketamine complicate the interpretation of both preclinical and clinical data. Moreover, the lack of controlled data demonstrating the ability of ketamine to sustain the antidepressant response with repeated administration leaves the potential clinical utility of this class of drugs in question. Using quantitative electroencephalography (qEEG) to objectively align doses of a low-trapping NMDA channel blocker, AZD6765 (lanicemine), to that of ketamine, we demonstrate the potential for NMDA channel blockers to produce antidepressant efficacy without psychotomimetic and dissociative side effects. Furthermore, using placebo-controlled data, we show that the antidepressant response to NMDA channel blockers can be maintained with repeated and intermittent drug administration. Together, these data provide a path for the development of novel glutamatergic-based therapeutics for treatment-refractory mood disorders.

Abstract Background Dopamine (DA) modulates long-term potentiation (LTP)-like neuroplasticity. While particularly D1 and D2 receptors are thought to influence neuroplasticity through glutamatergic N-methyl-D-aspartate (NMDA) receptor and gamma-aminobutyric acid (GABA) modulation, the exact mechanisms are not completely clarified. Objective We aimed to explore the relevance of NMDA receptor activity for DAergic modulation of focal LTP-like plasticity induced by excitatory paired associative stimulation (ePAS). Methods In a double-blinded, randomized, and placebo-controlled design, 17 healthy participants received DAergic agents (100 mg L-Dopa for general DAergic enhancement, 10 mg bromocriptine for selective D2 receptor activation, or placebo) with different doses of the partial NMDA receptor agonist D-cycloserine (CYC; 50, 100, 200 mg, or placebo) and underwent ePAS. Cortical excitability was monitored via motor-evoked potentials induced by TMS over the left motor cortex for up to 2 hours post-stimulation. Results We did not find significant interactions between DAergic agents, CYC, and time across the entire sample, but significant group differences depending on sensitivity to ePAS. In high-sensitivity, but not low-sensitivity participants, ePAS induced LTP-like effects. CYC produced nonlinear, dose-dependent effects on plasticity in both groups. In the high-sensitivity group, LTP-like effects persisted under both DAergic agents, but were significantly reduced under bromocriptine. CYC had a nonlinear effect when combined with bromocriptine. In the low-sensitivity group, ePAS under DAergic agents did not induce LTP-like effects, and only additional intervention with medium-dose CYC restored facilitatory effects under L-Dopa. Conclusions These findings suggest that optimal NMDA receptor activation is necessary for ePAS-induced neuroplasticity and that D2 receptor activity may reduce LTP-like effects by downregulating NMDA receptor function.

Anti-N-methyl-d-aspartate (NMDA) receptor encephalitis is a severe but treatable autoimmune disorder which diagnosis depends on sensitive and specific antibody testing. We aimed to assess the sensitivity and specificity of serum and CSF antibody testing in patients with anti-NMDA receptor encephalitis, and the relation between titres, relapses, outcome, and epitope repertoire. In this observational study, we used rat brain immunohistochemistry and cell-based assays (CBA) with fixed or live NMDA receptor-expressing cells to determine the sensitivity and specificity of antibody testing in paired serum and CSF samples. Samples were obtained at diagnosis from patients with anti-NMDA receptor encephalitis and from control participants worldwide. We deemed a patient to be antibody positive if their serum, their CSF, or both tested positive with both immunohistochemistry and CBA techniques; we determined titres with serial sample dilution using brain immunohistochemistry. We examined samples from 45 patients (25 with good outcome [modified Rankin Scale, mRS 0–2], ten with poor outcome [mRS 3–6], and ten with relapses) at three or more timepoints. We determined the epitope repertoire in the samples of 23 patients with CBA expressing GluN1-NMDA receptor mutants. We analysed samples from 250 patients with anti-NMDA receptor encephalitis and 100 control participants. All 250 patients had NMDA receptor antibodies in CSF but only 214 had antibodies in serum (sensitivity 100·0% [98·5–100·0%] vs 85·6% [80·7–89·4%], p<0·0001). Serum immunohistochemistry testing was more often in agreement with CBA with fixed cells (77 [71%] of 108) than with CBA with live cells (63 [58%] of 108, p=0·0056). In multivariable analysis, CSF and serum titres were higher in patients with poor outcome than in those with good outcome (CSF dilution 340 vs 129, difference 211, [95% CI 1–421], p=0·049; serum dilution 7370 vs 1243, difference 6127 [2369–9885], p=0·0025), and in patients with teratoma than in those without teratoma (CSF 395 vs 110, difference 285 [134–437], p=0·0079; serum 5515 vs 1644, difference 3870 [548–7193], p=0·024). Over time there was a decrease of antibody titres in the 35 patients with good or poor outcome and samples followed at three timepoints regardless of outcome (from diagnosis to last follow-up: CSF 614 to 76, difference 538 [288–788]; serum 5460 to 1564, difference 3896 [2428–5362]; both p<0·0001). Relapses were associated with a change in titre more often in CSF than in serum (14 of 19 vs seven of 16, p=0·037). After recovery, 24 of 28 CSF samples and 17 of 23 serum samples from patients remained antibody positive. Patients' antibodies targeted a main epitope region at GluN1 aminoacid 369; the epitope repertoire did not differ between patients with different outcomes, and did not change during relapses. The sensitivity of NMDA receptor antibody testing is higher in CSF than in serum. Antibody titres in CSF and serum were higher in patients with poor outcome or teratoma than in patients with good outcome or no tumour. The titre change in CSF was more closely related with relapses than was that in serum. These findings emphasise the importance of including CSF in antibody studies, and that antibody titres can complement clinical assessments. Dutch Cancer Society, National Institutes of Health, McKnight Neuroscience of Brain Disorders award, the Fondo de Investigaciones Sanitarias, ErasmusMC fellowship, and Fundació la Marató de TV3.

The NMDA ( N -methyl- d -aspartate) receptor transduces the binding of glutamate and glycine, coupling it to the opening of a calcium-permeable ion channel 1 . Owing to the lack of high-resolution structural studies of the NMDA receptor, the mechanism by which ion-channel blockers occlude ion permeation is not well understood. Here we show that removal of the amino-terminal domains from the GluN1–GluN2B NMDA receptor yields a functional receptor and crystals with good diffraction properties, allowing us to map the binding site of the NMDA receptor blocker, MK-801. This crystal structure, together with long-timescale molecular dynamics simulations, shows how MK-801 and memantine (a drug approved for the treatment of Alzheimer’s disease) bind within the vestibule of the ion channel, promote closure of the ion channel gate and lodge between the M3-helix-bundle crossing and the M2-pore loops, physically blocking ion permeation. A high-resolution X-ray structure and molecular dynamics simulations of the N -methyl- d -aspartate receptor in complexes with channel-blocking ligands reveals the molecular basis of the ligand binding and channel block.

Abstract Rationale Encephalitis caused by anti–N-methyl-d-aspartate receptor (NMDAR) antibodies is the leading cause of immune-mediated encephalitis. There are limited data on intensive care unit (ICU) management of these patients. Objectives To identify prognostic factors of good neurologic outcome in patients admitted to an ICU with anti-NMDAR encephalitis. Methods This was an observational multicenter study of all consecutive adult patients diagnosed with anti-NMDAR encephalitis at the French National Reference Centre, admitted to an ICU between 2008 and 2014. The primary outcome was a good neurologic outcome at 6 months after ICU admission, defined by a modified Rankin Scale score of 0–2. Measurements and Main Results Seventy-seven patients were included from 52 ICUs. First-line immunotherapy consisted of steroids (n = 61/74; 82%), intravenous immunoglobulins (n = 71/74; 96%), and plasmapheresis (n = 17/74; 23%). Forty-five (61%) patients received second-line immunotherapy (cyclophosphamide, rituximab, or both). At 6 months, 57% of patients had a good neurologic outcome. Independent factors of good neurologic outcome were early (≤8 d after ICU admission) immunotherapy (odds ratio, 16.16; 95% confidence interval, 3.32–78.64; for combined first-line immunotherapy with steroids and intravenous immunoglobulins vs. late immunotherapy), and a low white blood cell count on the first cerebrospinal examination (odds ratio, 9.83 for <5 vs. >50 cells/mm3; 95% confidence interval, 1.07–90.65). Presence of nonneurologic organ failures at ICU admission and occurrence of status epilepticus during ICU stay were not associated with neurologic outcome. Conclusions The prognosis of adult patients with anti-NMDAR encephalitis requiring intensive care is good, especially when immunotherapy is initiated early, advocating for prompt diagnosis and early aggressive treatment.

Metastasis—the disseminated growth of tumours in distant organs—underlies cancer mortality. Breast-to-brain metastasis (B2BM) is a common and disruptive form of cancer and is prevalent in the aggressive basal-like subtype, but is also found at varying frequencies in all cancer subtypes. Previous studies revealed parameters of breast cancer metastasis to the brain, but its preference for this site remains an enigma. Here we show that B2BM cells co-opt a neuronal signalling pathway that was recently implicated in invasive tumour growth, involving activation by glutamate ligands of N -methyl- d -aspartate receptors (NMDARs), which is key in model systems for metastatic colonization of the brain and is associated with poor prognosis. Whereas NMDAR activation is autocrine in some primary tumour types, human and mouse B2BM cells express receptors but secrete insufficient glutamate to induce signalling, which is instead achieved by the formation of pseudo-tripartite synapses between cancer cells and glutamatergic neurons, presenting a rationale for brain metastasis. Breast-to-brain metastasis is enabled by activation of an N -methyl- d -aspartate receptor, which is achieved via the formation of pseudo-tripartite synapses between cancer cells and glutamatergic neurons.