Sensitivity to MK-801 in phospholipase C-β1 knockout mice reveals a specific NMDA receptor deficit

Phospholipase C-β1 (PLC-β1) is a critical component of multiple signalling pathways downstream of neurotransmitter receptors. Mice lacking this enzyme display a striking behavioural phenotype with relevance to human psychiatric disease. Glutamatergic dysfunction is strongly associated with several abnormal behavioural states and may underlie part of the phenotype of the phospholipase C-β1 knockout (KO) mouse. A heightened response to glutamatergic psychotomimetic drugs is a critical psychosis-related endophenotype, and in this study it was employed as a correlate of glutamatergic dysfunction. Control (n=8) and PLC-β1 KO mice (n=6) were treated with MK-801, a NMDA receptor (NMDAR) antagonist, following either standard housing or environmental enrichment, and the motor function and locomotor activity thus evoked was assessed. In addition, MK-801 binding to the NMDAR was evaluated through radioligand autoradiography in post-mortem tissue (on a drug-naive cohort). We have demonstrated a significantly increased sensitivity to the effects of the NMDA antagonist MK-801 in the PLC-β1 KO mouse. In addition, we found that this mouse line displays reduced hippocampal NMDAR expression, as measured by radioligand binding. We previously documented a reversal of specific phenotypes in this mouse line following housing in an enriched environment. Enrichment did not alter this heightened MK-801 response, nor NMDAR expression, indicating that this therapeutic intervention works on specific pathways only. These findings demonstrate the critical role of the glutamatergic system in the phenotype of the PLC-β1 KO mouse and highlight the role of these interconnected signalling pathways in schizophrenia-like behavioural disruption. These results also shed further light on the capacity of environmental factors to modulate subsets of these phenotypes.

Clozapine reverses schizophrenia-related behaviours in the metabotropic glutamate receptor 5 knockout mouse: association with N-methyl-d-aspartic acid receptor up-regulation

Abnormalities in glutamatergic signalling are proposed in schizophrenia in light of the schizophreniform psychosis elicited by NMDA antagonists. The metabotropic glutamate receptor 5 (mGluR5) interacts closely with the NMDA receptor and is implicated in several behavioural endophenotypes of schizophrenia. We have demonstrated that mice lacking mGluR5 have increased sensitivity to the hyperlocomotive effects of the NMDA antagonist MK-801. Mice lacking mGluR5 also show abnormal locomotor patterns, reduced prepulse inhibition (PPI), and deficits on performance of a short-term spatial memory task on the Y-maze. Chronic administration of the antipsychotic drug clozapine ameliorated the locomotor disruption and reversed the PPI deficit, but did not improve Y-maze performance. Chronic clozapine increased NMDA receptor binding ([3H]MK-801) but did not alter dopamine D2 ([3H]YM-09151), 5-HT2A ([3H]ketanserin), or muscarinic M1/M4 receptor ([3H]pirenzepine), binding in these mice. These results demonstrate behavioural abnormalities that are relevant to schizophrenia in the mGluR5 knockout mouse and a reversal of behaviours with clozapine treatment. These results highlight both the interactions between mGluR5 and NMDA receptors in the determination of schizophreniform behaviours and the potential for the effects of clozapine to be mediated by NMDA receptor regulation.
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Functional (GT)n polymorphisms in promoter region of N-methyl-d-aspartate receptor 2A subunit (GRIN2A) gene affect hippocampal and amygdala volumes

The glutamate system including N-methyl-d-aspartate (NMDA) affects synaptic formation, plasticity and maintenance. Recent studies have shown a variable (GT)n polymorphism in the promoter region of the NMDA subunit gene (GRIN2A) and a length-dependent inhibition of transcriptional activity by the (GT)n repeat. In the present study, we examined whether the GRIN2A polymorphism is associated with regional brain volume especially in medial temporal lobe structures, in which the NMDA-dependent synaptic processes have been most extensively studied. Gray matter regions of interest (ROIs) for the bilateral amygdala and hippocampus were outlined manually on the magnetic resonance images of 144 healthy individuals. In addition, voxel-based morphometry (VBM) was conducted to explore the association of genotype with regional gray matter volume from everywhere in the brain in the same sample. The manually measured hippocampal and amygdala volumes were significantly larger in subjects with short allele carriers (n = 89) than in those with homozygous long alleles (n = 55) when individual differences in intracranial volume were accounted for. The VBM showed no significant association between the genotype and regional gray matter volume in any brain region. These findings suggest that the functional GRIN2A (GT)n polymorphism could weakly but significantly impact on human medial temporal lobe volume in a length-dependent manner, providing in vivo evidence of the role of the NMDA receptor in human brain development.

Metabotropic glutamate receptors as targets for novel antipsychotic treatments

In recent years metabotropic glutamate receptors have emerged as key targets for the design of new antipsychotic medications for schizophrenia, in particular mGluR5 and mGluR2/3. These receptors exhibit diverse interactions with other neurotransmitter receptors and critical elements of intracellular signalling cascades known to be important to the pharmacotherapy of schizophrenia. In addition, mGluR5 and mGluR2/3 are intimately involved in behavioural domains related to the symptoms of this disorder. Both animal and clinical studies using novel drugs targeting these receptors have provided encouraging results. The number of patents registered for drugs targeting metabotropic glutamate receptors has grown dramatically, and positive allosteric modulators for both receptors show particular promise.

Anti-inflammatory immunotherapy for multiple sclerosis/experimental autoimmune encephalomyelitis (EAE) disease

Multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), are inflammatory diseases of the central nervous system (CNS) characterized by localized areas with demyelination. Disease is believed to be an autoimmune disorder mediated by activated immune cells such as T- and B-lymphocytes and macrophages/microglia. Lymphocytes are primed in the peripheral tissues by antigens, and clonally expanded cells infiltrate the CNS. They produce large amounts of inflammatory cytokines, nitric oxide (NO) that lead to demyelination and axonal degeneration. Although several studies have shown that oligodendrocytes (OLGs), the myelin-forming glial cells in the CNS, are sensitive to cell death stimuli, such as cytotoxic cytokines, anti-myelin antibodies, NO, and oxidative stress, in vitro, the mechanisms underlying injury to the OLGs in MS/EAE remain unclear. The central role of glutamate receptors in mediating excitotoxic neuronal death in stroke, epilepsy, trauma and MS has been well established. Glutamate is the major excitatory amino acid transmitter within the CNS and it's signaling is mediated by a number of postsynaptic ionotropic and metabotropic receptors. Inflammation can be blocked with anti-cell adhesion molecules MAb, simultaneously protected oligodendrocytes and neurons against glutamate-mediated damage with the AMPA/kainate antagonist NBQX, and the NMDA receptor antagonist GPE, could thus be effective therapies for multiple sclerosis.

Future directions for pharmacotherapies for treatment-resistant bipolar disorder

Current pharmacological treatments for bipolar disorder (BD) are limited and efficacy has historically been discovered through serendipity. There is now scope for new drug development, focused on the underlying biology of BD that is not targeted by current therapies. The need for novel treatments is urgent when considering treatment resistant BD, where current therapies have failed. While established drugs targeting the monoamine systems continue to be worthwhile, new biological targets including inflammatory and oxidative an nitrosative pathways, apoptotic and neurotrophic pathways, mitochondrial pathways, the N-methyl-Daspartate (NMDA)-receptor complex, the purinergic system, neuropeptide system, cholinergic system and melatonin pathways are all being identified as potential anchors for the discovery of new agents. Many agents are experimental and efficacy data is limited, however further investigation may provide a new line for drug discovery, previously stalled by lack of corporate interest.

Peripheral proinflammatory markers associated with ketamine response in a preclinical model of antidepressant-resistance

© 2015 Elsevier B.V. Ketamine, N-methyl- d-aspartate (NMDA) receptor antagonist and anti-inflammatory agent, has rapid therapeutic effects in a subset of patients with more intractable forms of depression. Irregular proinflammatory cytokine and acute-reactive protein levels have been reported in clinical and preclinical depression research. We explored the association between the rapid antidepressant-like effects of ketamine and peripheral proinflammatory profile in a model of antidepressant-resistance. Male Wistar rats were pre-treated with ACTH-(1-24) 100. μg/d or saline (0.9%) for 14. d. Antidepressant-like effects were assessed with the forced swim test (FST). Ketamine (10. mg/kg) significantly reduced immobility duration in saline-pretreated control animals. In contrast, a divergent response was observed in ACTH-pretreated antidepressant resistant animals, with 50% responders and 50% non-responders. Plasma samples were analyzed via enzyme-linked immunosorbent assay (ELISA) for interleukin 6 (IL-6), tumour necrosis factor alpha (TNFα) and C-reactive protein (CRP). Levels of CRP and TNFα differentiated ketamine responders and non-responders.

The specificity of platelet glutamate receptor supersensitivity in psychotic disorders.

Hypoglutamatergic function is implicated in the pathogenesis of schizophrenia, and supersensitivity of platelet NMDA receptors has been reported in schizophrenia. The aim of this study was to examine the platelet glutamate receptor sensitivity in patients with schizophrenia (n=12), mania with psychotic features (n=10) and depression with psychotic features (n=10) and matched controls (n=12) in order to assess if this is a marker of schizophrenia or occurs in other psychotic conditions. Glutamate receptor sensitivity was assessed using the intracellular calcium response to glutamate measured with spectrofluorometry. The percentage response of the schizophrenic and depressed psychotic subjects to glutamate stimulation was significantly greater than control subjects (p<0.005). The mania with psychotic features group was not significantly different to controls. This data suggests that platelet glutamate receptors may be supersensitive in schizophrenia and depression with psychotic features. Furthermore, the platelet may be a possible peripheral marker of glutamate function in schizophrenia and depression with psychotic features.

Gene profiling reveals hydrogen sulphide recruits death signaling via the N-methyl-D-aspartate receptor identifying commonalities with excitotoxicity

Recently the role of hydrogen sulphide (H₂S) as a gasotransmitter stimulated wide interest owing to its involvement in Alzheimer's disease and ischemic stroke. Previously we demonstrated the importance of functional ionotropic glutamate receptors (GluRs) by neurons is critical for H₂S-mediated dose- and time-dependent injury. Moreover N-methyl-D-aspartate receptor (NMDAR) antagonists abolished the consequences of H₂S-induced neuronal death. This study focuses on deciphering the downstream effects activation of NMDAR on H₂S-mediated neuronal injury by analyzing the time-course of global gene profiling (5, 15, and 24 h) to provide a comprehensive description of the recruitment of NMDAR-mediated signaling. Microarray analyses were performed on RNA from cultured mouse primary cortical neurons treated with 200 µM sodium hydrosulphide (NaHS) or NMDA over a time-course of 5–24 h. Data were validated via real-time PCR, western blotting, and global proteomic analysis. A substantial overlap of 1649 genes, accounting for over 80% of NMDA global gene profile present in that of H₂S and over 50% vice versa, was observed. Within these commonly occurring genes, the percentage of transcriptional consistency at each time-point ranged from 81 to 97%. Gene families involved included those related to cell death, endoplasmic reticulum stress, calcium homeostasis, cell cycle, heat shock proteins, and chaperones. Examination of genes exclusive to H₂S-mediated injury (43%) revealed extensive dysfunction of the ubiquitin-proteasome system. These data form a foundation for the development of screening platforms and define targets for intervention in H₂S neuropathologies where NMDAR-activated signaling cascades played a substantial role. J. Cell. Physiol. 226: 1308–1322, 2011.

Platelet glutamate receptor supersensitivity in major depressive disorder.

Dysregulation of glutamate has been described in depression, and supersensitivity of platelet glutamate receptors has been found in both psychotic major depression and schizophrenia. The aim of this study was to examine the platelet glutamate receptor sensitivity in patients with nonpsychotic, unipolar major depression to assess whether this is a marker of depression or of psychosis. Glutamate receptor sensitivity was assessed using the platelet intracellular calcium response to glutamate (0-100 micromol) measured by spectrofluorometry. The depression group showed a significantly greater platelet intracellular calcium response to glutamate stimulation than the control group, both in terms of absolute values (p = 0.007) and percentage of response from baseline (p = 0.030). These data suggest that platelet glutamate receptors may be supersensitive in depression and that the platelet may be a possible peripheral marker of glutamate function in depression.

Supersensitive platelet glutamate receptors as a possible peripheral marker in schizophrenia.

Hypoglutamatergic function is implicated in the pathogenesis of schizophrenia. The aim of this study was to examine the platelet intracellular calcium response to glutamate using spectroflourometry in 15 schizophrenic patients and 15 matched control individuals as an index of platelet glutamate receptor sensitivity. Patients with schizophrenia had significantly lower baseline intracellular calcium levels than matched control individuals (P = 0.03). The percentage response of the schizophrenic individuals to glutamate stimulation was significantly greater than control individuals (P < 0.001). These data suggest that platelet glutamate receptors may be supersensitive in schizophrenia. Furthermore, the platelet may be a possible peripheral marker of glutamate function in schizophrenia.