Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system. Disturbances in glutamate transmission and NMDA receptor hypofunction are associated with schizophrenia. The NMDA receptor hypofunction hypothesis proposes that reduced NMDA receptor activity leads to increased mesolimbic dopamine activity causing positive symptoms and reduced mesocortical dopamine causing negative and cognitive symptoms. Several clinical studies have explored using NMDA agonists and drugs targeting downstream glutamate release as adjunctive treatments for schizophrenia with some success in improving symptoms. Ongoing research continues to develop new glutamatergic drugs for treating schizophrenia.
Lecture 7 from a college level neuropharmacology course taught in the spring 2012 semester by Brian J. Piper, Ph.D. (psy391@gmail.com) at Willamette University.
Lecture 7 from a college level neuropharmacology course taught in the spring 2012 semester by Brian J. Piper, Ph.D. (psy391@gmail.com) at Willamette University.
Neurohumoral transmission in central nervous systemRishabhchalotra
Neurohumoral Transmission in Central Nervous System (Detailed study about Neurotransmitters- Histamine, Serotonin, Dopamine, GABA, Glutamate, and Glycine).
Recent advances in the treatment of psychosesKarun Kumar
This presentation deals with atypical antipsychotics & new drugs in the pipeline (Clozapine, Risperidone, Olanzapine, Quetiapine, Ziprasidone, Aripiprazole, Second generation antipsychotics, atypical antipsychotics, Aspirin, Minocycline, Raloxifene, Estrogen, N-acetylcysteine). Introduction
Major psychiatric disorders Psychoses & affective disorders
Psychoses Disorders in which patients exhibit gross disturbances in their comprehension of reality as evidenced by false perception (hallucinations), false beliefs (delusions) and loss of contact with reality; schizophrenia most common form of psychosis (+ve n –ve symptoms)
Mostly concerned Abt –ve because poor prognosis , more difficult to treat, persist after positive symptoms have resolved
Mesolimbic Dopamine travels from the midbrain tegmental area to the nucleus accumbens. Increased activity in this pathway may cause delusions, hallucinations, and other so-called positive symptoms of schizophrenia.
Mesocortical pathways Decreased activity in the pathway that goes from the midbrain to the prefrontal lobe cortex can cause apathy, withdrawal, lack of motivation and pleasure, and other so-called negative symptoms of schizophrenia. Mesocortical dysfunction also disinhibits the mesolimbic pathway.
Nigrostriatal pathway from the substantia nigra to the striatum is involved in the coordination of body movements. Inhibition of this pathway causes the extrapyramidal side effects of antipsychotic drugs.
Tuberoinfundibular pathway from the hypothalamus to the pituitary inhibits the release of prolactin. Inhibition of this pathway leads to elevated serum prolactin levels.
2nd generation antipsychotics Clozapine, Risperidone, Olanazapine, Quetiapine, Ziprasidone, Aripiprazole (MOA, Dose, Brand name & A/E and receptor affinities)
Why do 1st gen. antipsychotics cause EPS & 2nd gen. do not? “Hit and run” hypothesis
Inflammation & schizophrenia
New drugs in pipeline Aspirin, Minocycline, Raloxifene, Estrogen, N-acetylcysteine (MOA and rationale of use)
Potential future targets of schizophrenia
My presentation on neurotransmitter glutamate. References from Comprehensive textbook of psychiatry 9th edition and Stahl's essential psychopharmacology 4th edition.
Here is an overview of Antipsychotics,starting from basic pathophysiology of Psychosis and Schizophrenia,breifing the Neuropharmacology and lastly introduction of drugs with special reference to side effects and clincal uses.
Via Christi Women's Connection presentation on advance in depression treatment by Matthew Macaluso, DO, medical director of Via Christi Psychiatric Clinic.
Neurohumoral transmission in central nervous systemRishabhchalotra
Neurohumoral Transmission in Central Nervous System (Detailed study about Neurotransmitters- Histamine, Serotonin, Dopamine, GABA, Glutamate, and Glycine).
Recent advances in the treatment of psychosesKarun Kumar
This presentation deals with atypical antipsychotics & new drugs in the pipeline (Clozapine, Risperidone, Olanzapine, Quetiapine, Ziprasidone, Aripiprazole, Second generation antipsychotics, atypical antipsychotics, Aspirin, Minocycline, Raloxifene, Estrogen, N-acetylcysteine). Introduction
Major psychiatric disorders Psychoses & affective disorders
Psychoses Disorders in which patients exhibit gross disturbances in their comprehension of reality as evidenced by false perception (hallucinations), false beliefs (delusions) and loss of contact with reality; schizophrenia most common form of psychosis (+ve n –ve symptoms)
Mostly concerned Abt –ve because poor prognosis , more difficult to treat, persist after positive symptoms have resolved
Mesolimbic Dopamine travels from the midbrain tegmental area to the nucleus accumbens. Increased activity in this pathway may cause delusions, hallucinations, and other so-called positive symptoms of schizophrenia.
Mesocortical pathways Decreased activity in the pathway that goes from the midbrain to the prefrontal lobe cortex can cause apathy, withdrawal, lack of motivation and pleasure, and other so-called negative symptoms of schizophrenia. Mesocortical dysfunction also disinhibits the mesolimbic pathway.
Nigrostriatal pathway from the substantia nigra to the striatum is involved in the coordination of body movements. Inhibition of this pathway causes the extrapyramidal side effects of antipsychotic drugs.
Tuberoinfundibular pathway from the hypothalamus to the pituitary inhibits the release of prolactin. Inhibition of this pathway leads to elevated serum prolactin levels.
2nd generation antipsychotics Clozapine, Risperidone, Olanazapine, Quetiapine, Ziprasidone, Aripiprazole (MOA, Dose, Brand name & A/E and receptor affinities)
Why do 1st gen. antipsychotics cause EPS & 2nd gen. do not? “Hit and run” hypothesis
Inflammation & schizophrenia
New drugs in pipeline Aspirin, Minocycline, Raloxifene, Estrogen, N-acetylcysteine (MOA and rationale of use)
Potential future targets of schizophrenia
My presentation on neurotransmitter glutamate. References from Comprehensive textbook of psychiatry 9th edition and Stahl's essential psychopharmacology 4th edition.
Here is an overview of Antipsychotics,starting from basic pathophysiology of Psychosis and Schizophrenia,breifing the Neuropharmacology and lastly introduction of drugs with special reference to side effects and clincal uses.
Via Christi Women's Connection presentation on advance in depression treatment by Matthew Macaluso, DO, medical director of Via Christi Psychiatric Clinic.
الطّباعة ثلاثيّة الأبعاد هي إحدى تقنيات التصنيع، حيث يتم تصنيع القطع عن طريق تقسيم التصاميم ثلاثية الأبعاد لها إلى طبقات صغيرة جدا باستخدام برامج الحاسوبية ومن ثم يتم تصنيعها باستخدام الطابعات ثلاثية الأبعاد عن طريق طباعة طبقة فوق الأخرى حتى يتكون الشكل النهائي.
تعريف الاقتصاد الرقمي
يعرف الاقتصاد الرقمي بأنه هو النشاط الناتج عن الاتصالات اليومية عبر الإنترنت، كما أن العمود الفقري له هو الارتباط التشعبي، ويعني تزايد الارتباط والترابط بين الأشخاص والمؤسسات والآلات، وتكنولوجيا الهاتف المحمول وإنترنت الأشياء. وهو عموما عبارة عن تصور لقطاع الأنشطة الاقتصادية ذات الصلة بالتقنية الرقمية. وتكون هذه الأنشطة مبنية على النماذج الاقتصادية الكلاسيكية أو الحديثة مثل نماذج الويب
التهديد المستمر المتقدم (Advanced persistent threat): هو مصطلح واسع يستخدم لوصف عملية هجوم يقوم فيها دخيل أو فريق من المتسللين بإنشاء وجود غير قانوني طويل الأمد على الشبكة من أجل استخراج البيانات شديدة الحساسية.
Nutraceutical market, scope and growth: Herbal drug technologyLokesh Patil
As consumer awareness of health and wellness rises, the nutraceutical market—which includes goods like functional meals, drinks, and dietary supplements that provide health advantages beyond basic nutrition—is growing significantly. As healthcare expenses rise, the population ages, and people want natural and preventative health solutions more and more, this industry is increasing quickly. Further driving market expansion are product formulation innovations and the use of cutting-edge technology for customized nutrition. With its worldwide reach, the nutraceutical industry is expected to keep growing and provide significant chances for research and investment in a number of categories, including vitamins, minerals, probiotics, and herbal supplements.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
1. Glutamate & Schizophrenia
Azimatul Karimah
Corresponding address : oe_tjie@yahoo.com
Asian Congress of Schizophrenia Research (ACSR), Bali 2013
2. Glutamate
• the major excitatory transmitter in the mammalian
central nervous system (CNS)
(Collingridge and Singer, 1990; Danysz et al., 1995; Collingridge and Bliss, 1995; Stone, 2011)
• sensitive to glutamate kills neurons through receptor-mediated
depolarization and calcium influx
(Obrenovitch and Urenjak, 1997; Parsons et al., 1998).
Excitotoxicity
(Rothman and Olney, 1987)
-Uci-
6. Glutamatergic Dysfunction
• schizophrenia, anxiety, depression (Danysz et al., 1995; Parsons et al.,
1998)
• associated with long term plastic changes in the CNS
chronic pain, drug tolerance, dependence, addiction,
partial complex seizures and tardive dyskinesia (Danysz et
al., 1995; Trujillo and Akil, 1995; Dickenson, 1997; Parsons et al., 1998).
• NMDA receptors regulate dopamine neurons
• the hypofunction of NMDA receptors abnormal
dopamine activity symptoms of schizophrenia
Stahl, 2007
-Uci-
7. Disturbance of glutamate
Disturbance of glutamate
the neurotoxic potential of endogenous glutamate
- increase in glutamate release,
- malfunctioning of neuronal and glial uptake,
- energy deficits
- neuronal depolarization,
- changes in glutamate receptor properties or expression patterns
- free radical formation,
- the presence of toxic proteins (ß-amyloid and tau in Alzheimer)
-Uci-
8. Glutamate-Dopamine Interaction
Ketamine, PCP
(glutamate antagonist)
Amphetamine
(dopamine agonist)
Positive
symptoms
Negative
symptoms
Cognitive
symptoms
1. Dopaminergic dysregulation may be “downstream” of
a primary deficit in NMDA function ???
2. Cognitive and negative symptoms arise from
abnormalities NMDA receptor ?
-Uci- (Javitt, 2010, Stone, 2011)
9. Hypothesis of Schizophrenia
The NMDA Receptor Hypofunction
• Hypoactivity NMDA in VTA can not inhibit mesolimbic
dopamine neurons positive symptoms
-Uci-
10. Hypothesis of Schizophrenia (2)
The NMDA Receptor Hypofunction
• NMDA receptor hypoactivity lose excitatory drive in mesocortical
dopamine neurons negative, cognitive and affective symptoms
-Uci-
11. Clinical Studies with NMDA Agonist
• 1st Generation : glycine modulatory site of the NMDA
receptor
• 2nd generation : glycine type I (GlyT1) transport
inhibitors (GTIs)
Javitt, 2010
-Uci-
12. Clinical Studies with NMDA Agonist
• Redox-sensitive site modulated by glutathione (GSH) N-acetylcysteine,
GSH precursor
• Pathological glutamate release compounds that inhibit
presynaptic glutamate release may also be therapeutic
Javitt, 2010
(2)
-Uci-
13. Result in Clinical Studies
Clinical trials Full NMDA Agonist (Glycine) + Antipsychotic
(Javitt, 2010)
-Uci-
14. Reduction of downstream
glutamate release
Lamotrigine
• Adjunctive treatment
• reverse positive, negative and cognitive symptoms
associated with ketamine administration in healthy
volunteers [Hosak and Libiger, 2002]
• an add-on medication for patients who are only
partially responsive to clozapine, in modest effect
[Tiihonen et al. 2009].
-Uci-
15. Reduction of downstream
glutamate release (2)
mGlu2/3 receptor agonist (LY2140023)
• Agonist inhibit synaptic glutamate release NMDA
recepor antagonist [Javitt, 2004;Moghaddam, 2004]
- Improvement positive and negative symptoms vs
placebo (Patil et al, 2007)
-Uci-
16. Reduction of downstream
glutamate release (3)
mGlu2/3 receptor agonist (LY2140023)
• Vs Olanzapine 15mg daily, no significant difference of
response to positive and negative symptoms
• No elevated prolactin, weight gain or EPS
• AE : affective lability, mild reduction of body weigh and
BMI, convulsions occurred in 3 out of the 669 patients
recruited [Kinon et al. 2010].
-Uci-
17. Reduction of downstream
glutamate release (4)
mGlu2/3 agonists
• work primarily through dopaminergic mechanisms [Seeman
and Guan, 2009].
• downstream effects reducing D2 High expression [Seeman
et al. 2009].
-Uci-
18. Reduction of downstream
glutamate release (5)
Topiramate
• Adjunctive treatment [Tiihonen et al. 2005]
• AMPA Antagonist by enhancing GABA transmission
• AMPA antagonism only occurs at higher concentrations
[Gibbs et al. 2000].
-Uci-
19. Other Mechanism
Mynocycline
• inhibit the effects of NMDA receptor antagonism on rats
[Levkovitz et al. 2007; Zhang et al. 2007]
• reverse PCP-induced cognitive deficits [Fujita et al. 2008].
• A double-blind, randomized controlled trial as add-on
treatment in early phase schizophrenia (< 5 year)
revealed a significant effect on negative and cognitive
symptoms [Levkovitz et al. 2010].
• Uncertained mechanism, the inhibition of glutamate
excitotoxicity [Pi et al. 2004; Wilkins et al. 2004].
-Uci-
20. Other Mechanism (2)
Canabidiol (CBD)
• a modulatory effect on glutamatergic transmission, [Long
et al. 2006; Moreira and Guimaraes, 2005,[Hallak et al. 2011]
• acute intoxication with cannabis
low CBD = impairments in recall,
high CBD did not induce any cognitive deficits
[Morgan et al. 2010]
• Effective as an antipsychotic in patients with
schizophrenia, no additional beneficial effect in a
small open-label study of clozapine-resistant patients
[Zuardi et al. 2006]
-Uci-
22. Conclussion
• Glutamatergic pathway is known as one mechanism on
developing psychopathology of schizophrenia
• The mechanism associates indirectly with other
neurotransmitter systems such as dopamine and GABA
• Until now, there are many studies of developing
glutamatergic agent for treating schizophrenia that
would be promising in the future
-Uci-
Editor's Notes
Reseptor ini terkait dengan kanal ion bagi ion Na dan Ca
memiliki afinitas terhadap ion Mg++ Akibatnya ion Mg++ dapat
mengikat reseptor NMDA dan memblokade kanal yang sedianya
akan dilewati oleh ion Na+ atau Ca++.
Tetapi jika terjadi depolarisasi, afinitas Mg++ dengan reseptor
tersebut menjadi berkurang Mg++ akan terlepas dan kanal tidak
lagi terblokade Karena itu, aktivitas reseptor NMDA memerlukan
reseptor lain untuk menginisiasi aktivasinya, yaitu reseptor glutamat
non-NMDA
An important descending glutamatergic pathway projects from cortical pyramidal neurons to dopamine neurons in the ventral tegemental area (Figure 3A, left panel). This descending cortico-brainstem glutamate pathway normally acts as a brake on the mesolimbic dopamine pathway. It does this by communicating with these dopamine neurons through an inhibitory γ-aminobutyric acid interneuron in the ventral tegmental area (VTA) (Figure 3A, left panel). This normally results in tonic inhibition of dopamine release from the mesolimbic pathway. However, if NMDA receptors in the VTA are hypoactive in untreated schizophrenia, and thus cannot do their job of tonically inhibiting mesolimbic dopamine neurons, this would cause mesolimbic dopamine hyperactivity and the positive symptoms of psychosis
cortico-brainstem glutamate neurons synapse directly upon those dopamine neurons in the VTA that project to the cortex, those so-called mesocortical dopamine neurons (Figure 4A, left panel). This means that cortico-brainstem glutamate neurons normally function as accelerators of these mesocortical dopamine neurons and, therefore, they tonically excite them (Figure 4A, left panel). The consequence of this neuronal circuitry is that when cortico-brainstem projections to mesocortical dopamine neurons have NMDA receptor hypoactivity, they lose their excitatory drive and become hypoactive, as shown in Figure 4B (right panel). This could hypothetically explain why mesocortical dopamine neurons are hypoactive. Thus, their link to the cognitive, negative, and affective symptoms of schizophrenia shown in Figure 4B (right panel).
An important descending glutamatergic pathway projects from cortical pyramidal neurons to dopamine neurons in the ventral tegemental area (Figure 3A, left panel). This descending cortico-brainstem glutamate pathway normally acts as a brake on the mesolimbic dopamine pathway. It does this by communicating with these dopamine neurons through an inhibitory γ-aminobutyric acid interneuron in the ventral tegmental area (VTA) (Figure 3A, left panel). This normally results in tonic inhibition of dopamine release from the mesolimbic pathway. However, if NMDA receptors in the VTA are hypoactive in untreated schizophrenia, and thus cannot do their job of tonically inhibiting mesolimbic dopamine neurons, this would cause mesolimbic dopamine hyperactivity and the positive symptoms of psychosis
Studies with naturally occurring compounds to date have primarily used glycine, administered at a dose of up to 800 mg/kg (approx. 60 g/d) (109-112); D-serine, administered at a dose of 30 mg/kg (approx. 2.1 g/d) or D-alanine administered at a dose of 100 mg/kg; and sarcosine, administered at a dose of
30 mg/kg (approx. 2.1 g/d). For glycine, this represents the highest practical dose because of the quantity of amino acid needed to significantly increase
brain glycine levels. For other compounds, formal dose findings studies have not been performed, and maximum tolerated doses are presently unknown
Summary of clinical trials performed to date with
full NMDA agonists combined with antipsychotics other than
clozapine. Studies were conducted using the amino acid glycine
at doses of 0.4-0.8 g/kg (30-60 g/d) unless otherwise indicated.
Further details about individual studies are provided in (83).
CONSIST refers to The Cognitive and Negative Symptoms in
Schizophrenia Trial (132). Statistics were calculated as weighted
average of % change scores for negative symptoms, across trials.
Second, based upon the observation that NMDA blockade leads to rebound increases in glutamate release that may themselves be pathological (96), it has been proposed that compounds that inhibit presynaptic glutamate release may also be therapeutic. Examples of such compounds include the anti-epilepsy drug lamotrigine and agonists of metabotropic glutamate type 2/3 (mGluR2/3) receptors, which are localized to presynaptic glutamate terminals in prefrontal cortex. mGluR2/3 agonists have been shown to be effective in reversing behavioral effects of NMDA antagonists in rodent models (98), supporting the potential efficacy of these compounds as novel antipsychotic agents. In addition, both lamotrigine and mGluR 2/3 agonists have also been shown to reverse clinical effects of ketamine during acute challenge in normal volunteers, further supporting the applicability of basic models to humans. In general, therefore, as the NMDA model reaches its second decade, the base of treatment development based upon glutamatergic theories continues to increase.
Glutamate mGlu 2/3 receptors are presynaptic
autoreceptors [Kew and Kemp, 2005]. Agonists
inhibit synaptic glutamate release (Figure 6), and
have been shown to reduce the effects of NMDA
receptor antagonists, and amphetamine in both
animal and human studies [Javitt, 2004;
Moghaddam, 2004]. A recent phase II trial of an
mGlu2/3 receptor agonist (LY2140023, an oral
prodrug of LY404039), in a sample of patients
with chronic schizophrenia, reported significant
improvement in positive and negative symptoms
compared with placebo [Patil et al. 2007].
Second, based upon the observation that NMDA blockade leads to rebound increases in glutamate release that may themselves be pathological (96), it has been proposed that compounds that inhibit presynaptic glutamate release may also be therapeutic. Examples of such compounds include the anti-epilepsy drug lamotrigine and agonists of metabotropic glutamate type 2/3 (mGluR2/3) receptors, which are localized to presynaptic glutamate terminals in prefrontal cortex. mGluR2/3 agonists have been shown to be effective in reversing behavioral effects of NMDA antagonists in rodent models (98), supporting the potential efficacy of these compounds as novel antipsychotic agents. In addition, both lamotrigine and mGluR 2/3 agonists have also been shown to reverse clinical effects of ketamine during acute challenge in normal volunteers, further supporting the applicability of basic models to humans. In general, therefore, as the NMDA model reaches its second decade, the base of treatment development based upon glutamatergic theories continues to increase.
Glutamate mGlu 2/3 receptors are presynaptic
autoreceptors [Kew and Kemp, 2005]. Agonists
inhibit synaptic glutamate release (Figure 6), and
have been shown to reduce the effects of NMDA
receptor antagonists, and amphetamine in both
animal and human studies [Javitt, 2004;
Moghaddam, 2004]. A recent phase II trial of an
mGlu2/3 receptor agonist (LY2140023, an oral
prodrug of LY404039), in a sample of patients
with chronic schizophrenia, reported significant
improvement in positive and negative symptoms
compared with placebo [Patil et al. 2007].
Other metabotropic ligands, including mGluR5
(101, 102) and mGluR8 (103) agonists, have also
been proposed as potential treatments for schizophrenia,
based upon their ability to modulate NMDA
receptor-mediated neurotransmission (104). Finally,
N-acetylaspartylglutamate (NAAG) may be an endogenous
ligand for mGlu2/3 receptors in CNS. NAAG is
broken down by NAAG peptidase (glutamate carboxypeptidase
II) (105). Compounds that inhibit NAAG
peptidase, such as an experimental inhibitor termed
ZJ43, would therefore lead to increased mGlu2/3 occupancy.
This compound has been tested preclinically and
shown to inhibit PCP- and MK-801-induced behaviors
in animals, consistent with an effect on NMDA receptor-
mediated neurotransmission (106, 107).
Finally, some authors have suggested that NMDA
antagonists may be beneficial, based upon concepts
that cognitive deficits in schizophrenia may result from
hyper-glutamatergic neurotoxicity (13). Examples of
compounds that have been considered based upon
this hypothesis are AMPA antagonists and the anti-
Alzheimers disease drug memantine. To date, however,
clinical experience with NMDA antagonists has not
been encouraging (108).
Other metabotropic ligands, including mGluR5
(101, 102) and mGluR8 (103) agonists, have also
been proposed as potential treatments for schizophrenia,
based upon their ability to modulate NMDA
receptor-mediated neurotransmission (104). Finally,
N-acetylaspartylglutamate (NAAG) may be an endogenous
ligand for mGlu2/3 receptors in CNS. NAAG is
broken down by NAAG peptidase (glutamate carboxypeptidase
II) (105). Compounds that inhibit NAAG
peptidase, such as an experimental inhibitor termed
ZJ43, would therefore lead to increased mGlu2/3 occupancy.
This compound has been tested preclinically and
shown to inhibit PCP- and MK-801-induced behaviors
in animals, consistent with an effect on NMDA receptor-
mediated neurotransmission (106, 107).
Finally, some authors have suggested that NMDA
antagonists may be beneficial, based upon concepts
that cognitive deficits in schizophrenia may result from
hyper-glutamatergic neurotoxicity (13). Examples of
compounds that have been considered based upon
this hypothesis are AMPA antagonists and the anti-
Alzheimers disease drug memantine. To date, however,
clinical experience with NMDA antagonists has not
been encouraging (108).
Studies of other mechanisms also show suggestive findings. Thus, one study of N-acetylcysteine, a precursor of glutathione, produced significant improvement in PANSS total and negative symptoms in schizophrenia , along with improvement in generation of MMN, which may serve as a biomarker of NMDA dysfunction . Two small studies with lamotrigine showed suggestive results, although a subsequent multicenter double-blind study was negative. To date, one phase II study with the oral mGluR2/3 agonist prodrug LY2140023, used as monotherapy in acutely relapsing subjects, showed clinical efficacy similar to that of olanzapine with markedly reduced incidence of metabolic side effects. Although this study requires replication, it is encouraging with regard to overall efficacy of glutamatergic
approaches.