logging in or signing up a bunty_jagiwala Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 437 Category: Science & Tech.. License: All Rights Reserved Like it (4) Dislike it (0) Added: October 10, 2009 This Presentation is Public Favorites: 2 Presentation Description No description available. Comments Posting comment... By: nayira (18 month(s) ago) This presentation is very informative. Please make it in a downloaded form or please send it to me Saving..... Post Reply Close Saving..... Edit Comment Close By: Meghapatel106 (18 month(s) ago) please send this to me..its very much informative Saving..... Post Reply Close Saving..... Edit Comment Close By: lamieess (19 month(s) ago) please i need this presentation please download it to me Saving..... Post Reply Close Saving..... Edit Comment Close By: raj_patel (23 month(s) ago) Hi this presentation is very informative. Please make it downloaded form. Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript MOLECULAR PHARMACOLOGYA SEMINAR ON NMDA RECEPTORS(NMDA=N-methyl D-aspartate) : MOLECULAR PHARMACOLOGYA SEMINAR ON NMDA RECEPTORS(NMDA=N-methyl D-aspartate) GUIDED BY:- PRESENTED BY:- Mrs. Versha J. Galani Biren H. Shah M.Pharm (Ph.’cology) 09PLY02 (SEM.-1) INTRODUCTION : INTRODUCTION What is receptor? it is defined as a specific binding site with functional correlate(s). what is neurotransmitter? It is a substance released by a neuron, acting rapidly, briefly and at short range on the membrane of adjacent neuron, producing a change in conductance which either increase or decreases the excitability of the post syneptic cell. NEUROTRANSMITTERS IN CNS : NEUROTRANSMITTERS IN CNS Noradrenaline Dopamine Serotonin Acetylcholine AMINO ACID TRANSMITTERS GABA Glutamate Aspartate Glycine TYPES OF AMINO ACID TRANSMITTERS : TYPES OF AMINO ACID TRANSMITTERS EXCITATORY AMINO-ACIDS AS CNS TRANSMITTERS : EXCITATORY AMINO-ACIDS AS CNS TRANSMITTERS Unravelling some of the complexities of amino acids reeptors and signalling mechanisms has thrown considerable light on their role in brain function and their likely involvement in CNS disease. L-Glutamate is the principal and ubiquitous excitatory transmitter in the CNS. Aspartate Plays excitatory role in certain brain regions and homocysteate. This role of aspartate is controversial. Function of glutamate : Function of glutamate Is the most prominent neurotrnsmitter in the body being present in over 50% of the nervous tissues. Glutamate was initially discovered to be a neurotransmitter following insect studies in the early1960s. The primary glutamae receptor is specifically sensitive to NMDA,which cause direct action of the central pore of the receptor,an ion channel, to drive the neuron to depolarize. Depolarization will trigger the primary firing or actio potential of the neuron,therefore NMDA is excitation. METABOLISM OF TRANSMITTER AMINO ACIDS IN THE BRAIN.Transmitter substances are marked with green boxes.gaba-t=gaba transaminase,gad=glutamic acid decarboxylase : METABOLISM OF TRANSMITTER AMINO ACIDS IN THE BRAIN.Transmitter substances are marked with green boxes.gaba-t=gaba transaminase,gad=glutamic acid decarboxylase METABOLISM & release of AMINO ACIDS IN THE BRAIN : METABOLISM & release of AMINO ACIDS IN THE BRAIN Glutamate is widely & fairly uniformly distributed in the CNS. Glutamate in the CNS comes mainly from eiher glucose,via the crebs cycle,or glutamine, which is synthesized by glial cells & taken up by the neurons. The metabolic & neurotransmitter pools being linked by transaminase enzyme that catalyze the interconversion of glutamate & α-oxoglutarate There is interconnection between the pathways for the synthesis of EEAs & inhibitory amino acids (GABA &Glycine).s Transport of glutamate (glu)and glutamine(gln) by neurons and astrocytes.Eaat=excitatory amino acid transporter,GlnT=glutamine transporter : Transport of glutamate (glu)and glutamine(gln) by neurons and astrocytes.Eaat=excitatory amino acid transporter,GlnT=glutamine transporter Transport & release of glutamate &glycine : Transport & release of glutamate &glycine Glutamate is stored in synaptic vesicles and released by Ca+2 dependent exocytosis. specific transporter proteins account for its uptake by neurons and other cells. Released glutamate is taken up by cells in exchange for Na and transported driven by the proton gradient across the vesicles membrane. Many drugs(not in clinical use)are known that interfere specifically with glutamate. The action of glutamate is terminated mainly by carrier-mediated reuptake into the nerve terminals and neighboring astrocytes. This transport can, under some circumstances operate in reverse and constitute a source of glutamate release, a process that may occur under pathological condition such as brain ischemia. Function of glutamate : Function of glutamate Is the most prominent neurotrnsmitter in the body being present in over 50% of the nervous tissues. Glutamate was initially discovered to be a neurotransmitter following insect studies in the early1960s. The primary glutamae receptor is specifically sensitive to NMDA,which cause direct action of the central pore of the receptor,an ion channel, to drive the neuron to depolarize. Depolarization will trigger the primary firing or actio potential of the neuron,therefore NMDA is excitation. Slide 12: The NMDA receptor (NMDAR), a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function. The NMDAR is a specific type of ionotropic glutamate receptor. NMDA (N-methyl D-aspartate) is the name of a selective agonist that binds to NMDA receptors but not to other glutamate receptors. Activation of NMDA receptors results in the opening of an ion channel that is nonselective to cations. A unique property of the NMDA receptor is its voltage-dependent activation, a result of ion channel block by extracellular Mg2+ ions. This allows voltage-dependent flow of Na+ and small amounts of Ca2+ ions intoThe NMDA receptor (NMDAR), a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function Slide 13: The NMDAR is a specific type of ionotropic glutamate receptor. NMDA (N-methyl D-aspartate) is the name of a selective agonist that binds to NMDA receptors but not to other the cell and K+ out of the cell. Calcium flux through NMDARs is thought to play a critical role in synaptic plasticity, a cellular mechanism for learning and memory. The NMDA receptor is distinct in two ways: First, it is both ligand-gated and voltage-dependent; second, it requires co-activation by two ligands - glutamate and glycine. Types of glutamate receptors : Types of glutamate receptors Can be divided in to two groups according to the mechanism by which their activation gives rise to a postsynaptic current. Ionotropic glutamate receptors from the ion channel pore that activates when glutamate binds to the receptor. Metabotropic glutamate receptors indirectly activate ion-channels on the plasma membrane through a signaling cascade that involves G-protein. Pharmacology of nmda receptors : Pharmacology of nmda receptors Slide 17: Molecular Biology Two major subunit families designated NR1, NR2 as well as a modulatory subunit designated NR3 have been cloned. Most functional receptors in the mammalian CNS are formed by combination of NR1 and NR2 subunits which express the glycine and glutamate recognition sites respectively. NR1 Subunits Alternative splicing generates eight isoforms for the NR1 subfamily . The variants arise from splicing at three exons one encodes a 21-amino acid insert in the N-terminal domain (N1, exon 5), and two encode adjacent sequences of 37 and 38 amino acids in the C-terminal domain (C1, exon 21 and C2, exon 22). NR1 variants are sometimes denoted by the presence or absence of these three alternatively spliced exons (from N to C1 to C2). NR1111 has all three exons, NR1000 has none, and NR1100 has only the N-terminal exon. The variants from NR1000 to NR1111 are alternatively denoted as NMDAR1E, C, D, A, G, F, “H” and B respectively or NMDAR1-4a,-2a,-3a,-1a,-4b,-2b,-3b and-1b respectively, but the more frequent terminology using non-capitalized suffices for the most common splice variants is NR1a (NR1011 or NMDAR1A) and NR1b (NR1100 or NMDARIG). MRNA for double splice variants in the C1/C2 regions such as NR1011 (NR1a) show an almost complementary pattern to those lacking both of these inserts such as as Nr2 subunite : Nr2 subunite Slide 19: NR2 Subunits The NR2 subfamily consists of four individual subunits, NR2A to NR2D. Various heteromeric NMDA receptor channels formed by combinations of NR1 and NR2 subunits are known to differ in gating properties, Mg2+ sensitivity and pharmacological profile (Sucher et al., 1996). The heteromeric assembly of NR1 and NR2C subunits for instance, has a lower sensitivity to Mg2+ but increased sensitivity to glycine and a very restricted distribution in the brain. In situ hybridization has revealed overlapping but different expression for NR2 mRNA e.g. NR2A mRNA is distributed ubiquitously like NR1 with highest densities occurring in hippocampal regions and NR2B is expressed predominantly in forebrain but not in cerebellum where NR2C predominates. The spinal cord expresses high levels of NR2C and NR2D (Tolle et al., 1993) and these may form heteroligomeric receptors with NR1 plus NR2A which would provide a basis for the development of drugs selectively aimed at spinal cord disorders(Sundstrom et al., 1997). NMDA receptors cloned from murine CNS have a different terminology to those in the rat: z1 remains the terminology for the mouse equivalent of NR1 and e1 to e4 represent NR2A to 2D subunits respectively. Slide 20: NR3 Subunits NR3 (NRL or Chi-1) is expressed predominantly in the developing CNS and does not seem to form functional homomeric glutamate-activated channels but co-expression of NR3 with NR1 plus NR2 subunits decreases response magnitude (Sucher et al., 1995; Kinsley et al., 1999; Matsuda et al., 2002). However, NR3A or NR3B do co-assemble with NR1 alone in Xenopus oocytes to form excitatory glycine receptors that are unaffected by glutamate or NMDA, Ca2+-impermeable, resistant to blockade by Mg2+ uncompetitive and competitive antagonists and actually inhibited by the glycine co-agonist D-serine. (Chatterton et al., 2002) Special features of nmda receptors : Special features of nmda receptors They are highly permeable to ca,as well as to other cations,so activation of NMDA receptors is particularly effctivein promoting ca entry. They are readily blocked by Mg,and this block shows marked voltage dependence.it occures at physiological Mg concentration if the cell is depoarised. Aaaactivation of NMDA receptors requires glycine as well as glutamate.the binding site for glycine is distinct from the glutamate binding site,and both have to be occupied for the channel to open. Facillation of Nmda by glycine : Facillation of Nmda by glycine Slide 23: Agonists Activation of NMDA receptors requires binding of glutamate or aspartate (aspartate does not stimulate the receptors as strongly). In addition, NMDARs also require the binding of the co-agonist glycine for the efficient opening of the ion channel, which is a part of this receptor. D-serine has also been found to co-agonize the NMDA receptor with even greater potency than glycine. D-serine is produced by serine racemase, and is enriched in the same areas as NMDA receptors. Removal of D-serine can block NMDA-mediated excitatory neurotransmission in many areas. Recently, it has been shown that D-serine is synthesized mostly by neurons, indicating a role for neuron-derived D-serine in NMDA receptor regulation. Main site of drug action nmda : Main site of drug action nmda Mechanism of action : Mechanism of action The NMDA receptor is an ionotropic receptor that allows for the transfer of electrical signals between neurons in the brain and in the spinal column. For electrical signals to pass, the NMDA receptor must be open. To remain open, an NMDA receptor must bind to glutamate and to glycine. An NMDA receptor that is bound to glycine and glutamate and has an open ion channel is called "activated." Chemicals that deactivate the NMDA receptor are called antagonists. NMDAR antagonists fall into four categories: Competitive antagonists, which bind to and block the binding site of the neurotransmitter glutamate; glycine antagonists, which bind to and block the glycine site; noncompetitive antagonists, which inhibit NMDARs by binding to allosteric sites; and uncompetitive antagonists, which block the ion channel by binding to a site within it. examples : examples Competitive antagonists AP5P (APV, R-2-amino-5-phosphonopentanoate) AP7 (2-amino-7-phosphonoheptanoic acid) CPPene (3-[(R)-2-carboxypiperazin-4-yl]-prop-2-enyl-1-phosphonic acid) Uncompetitive channel blockers Amantadine: used for treating Parkinson's diseases and influenza and Alzhiemer's. Dextromethorphan: a common antitussive found in cough medicines. Dextrorphan: active metabolite of dextromethorphan. Schedule I in the US. Ibogaine: a Schedule I controlled substance in the United States. Ketamine: an animal and human anesthetic and recreational drug. Slide 28: Memantine: moderate affinity, voltage-dependent uncompetitive antagonist. Approved in the U.S. by the Food and Drug Administration for the treatment of Alzheimer's disease. Nitrous oxide: used for anesthesia, particularly in dentistry. Phencyclidine: a Schedule II controlled substance in the United States. Riluzole: used to treat amyotrophic lateral sclerosis. Tiletamine: an animal anesthetic. Non-competitive antagonists Aptiganel (Cerestat, CNS-1102): binds the Mg2+ binding site within the channel of the NMDA receptor. Dizocilpine (MK-801): an experimental drug. HU-211: an enantiomer of the potent cannabinoid HU-210 which lacks cannabinoid effects and instead acts as a potent non-competitive NMDA antagonist. Remacemide: principle metabolite is an uncompetitive antagonist with a low affinity for the binding site. Glycine antagonists These drugs act at the glycine binding site: 1-Aminocyclopropanecarboxylic acid (ACPC) 7-Chlorokynurenate DCKA (5,7-dichlorokynurenic acid) Kynurenic acid: a naturally occurring antagonist Lacosamide: an investigational drug for the treatment of epilepsy and diabetic neuropathic pain. Mechanism of long term potentiation : Mechanism of long term potentiation A With infrequent synaptic activity, glutamate activates mainly AMPA-receptors. There is insufficient glutamate to activate metabotropic (met) receptors, and NMDA-receptor channels are blocked by Mg2+. B After a conditioning train of stimuli, enough glutamate is released to activate metabotropic receptors, and NMDA channels are unblocked by the sustained depolarisation. The resulting increase in [Ca2+]i activates PKC and NOS. PKC phosphorylates various proteins, including AMPA-receptors (causing facilitation of transmitter action) and other signal transduction molecules controlling gene transcription (not shown) in the postsynaptic cell. Release of NO facilitates glutamate release (retrograde signalling, otherwise known as NO turning back). (G, glutamate; NMDA, N-methyl-d-aspartate; AMPA, α-amino-3-hydroxy-5-methylisoxazole; PI, phosphatidylinositol; IP3, inositol 1,4,5-trisphosphate; DAG, diacylglycerol; PKC, protein kinase; NO, nitric oxide; NOS, nitric oxide synthase.) Slide 32: NMDA antagonists prevent LTP, without affecting normal, non-potentiated transmission (which depends on AMPA-receptors). Disruption of the gene for the NMDA-receptor has the same effect. LTP occurs only if the postsynaptic cell is depolarised at the time when the conditioning burst of stimulation is delivered. Blocking AMPA-receptors prevents this and prevents LTP. Antagonists at metabotropic glutamate receptors reduce the duration of LTP; LTP is also impaired in transgenic mice lacking the mGluR1 receptor. Calcium entry into the postsynaptic cell is required, and there is evidence that activation of protein kinase C , resulting in phosphorylation of AMPA-receptors, is involved in the mechanism of potentiation. LTP is reduced by agents that block the synthesis or effects of nitric oxide or arachidonic acid. One or both of these mediators may be the hitherto elusive 'retrograde messenger' through which events in the postsynaptic cell are able to influence the presynaptic nerve terminal Alzheimer's disease Misprocessing of amyloid precursor protein (APP) in Alzheimer's disease disrupts LTP and is thought to lead to early cognitive decline in individuals with the disease. LTP has received much attention among those who study Alzheimer's disease (AD), a neurodegenerative disease that causes marked cognitive decline and dementia. Much of this deterioration occurs in association with degenerative changes in the hippocampus and other medial temporal lobe structures. Because of the hippocampus' well established role in LTP, some have suggested that the cognitive decline seen in individuals with AD may result from impaired LTP. Glutamate excitotoxicity : Glutamate excitotoxicity Slide 34: Glutamate Excitotoxicity High concentrations of glutamate produce neuronal cell death . Initially, the cascade of events leading to neuronal death was thought to be triggered exclusively by excessive activation of NMDA or AMPA/kainate receptors, allowing significant influx of Ca2+ into the neurons. Such glutamate neurotoxicity was thought to underlie the damage that occurs after ischemia or hypoglycemia in the brain, during which a massive release and impaired reuptake of glutamate in the synapse would lead to excess stimulation of glutamate receptors and subsequent cell death. Although NMDA receptor antagonists can attenuate neuronal cell death induced by activation of these receptors , even the most potent antagonists cannot prevent all such damage, causing additional efforts to salvage the therapeutic potential for glutamate antagonists as neuroprotectants. More recent studies implicate both local depletion of Na+ and K+, as well as small but significant elevations of extracellular Zn2+ as factors that can activate both necrotic and pro-apoptotic cascades, leading to neuronal death. Because of the widespread distribution of glutamate receptors in the CNS, they have become targets for diverse therapeutic interventions. For example, a role for disordered glutamatergic transmission in the etiology of chronic neurodegenerative diseases and in schizophrenia has been postulated. Uses and effects : Uses and effects NMDA receptor antagonists induce a state called dissociative anesthesia, marked by catalepsy, amnesia and analgesia. Ketamine and other NMDA receptor antagonists are most frequently used in conjunction with diazepam as anesthesia in cosmetic or reconstructive plastic surgery and in the treatment of burn victims. Ketamine is a favored anesthetic for emergency patients with unknown medical history because it depresses breathing and circulation less than other anesthetics. The NMDA receptor antagonist dextromethorphan is one of the most commonly used cough suppressants in the world. Slide 36: Depressed NMDA receptor function is associated with an array of negative symptoms. For example, NMDA receptor hypofunction that occurs as the brain ages may be partially responsible for memory deficits associated with aging. Schizophrenia may also have to do with irregular NMDA receptor function (the "glutamate hypothesis" of schizophrenia). Increased levels of another NMDA antagonist, kynurenic acid, may aggravate the symptoms of schizophrenia, according to the "kynurenic hypothesis". NMDA receptor antagonists can mimic these problems; they sometimes induce "psychotomimetic" side effects, symptoms resembling psychosis. Such side effects caused by NMDA receptor inhibitors include hallucinations, paranoid delusions, confusion, difficulty concentrating, agitation, alterations in mood, nightmares, catatonia, ataxia, anaesthesia, and learning and memory deficits. Because of these psychotomimetic effects, NMDA receptor antagonists, especially phencyclidine, ketamine, and dextromethorphan, are used as recreational drugs. At subanesthetic doses, these drugs have mild stimulant effects, and at higher doses, begin inducing dissociation and hallucinations. Most NMDA receptor antagonists are metabolized in the liver. Frequent administration of most NMDA receptor antagonists can lead to tolerance, whereby the liver will more quickly eliminate NMDA receptor antagonists from the bloodstream. Role of nmda antagonists in treatment of alzheimer’s disease : Role of nmda antagonists in treatment of alzheimer’s disease Memantine is the first in a novel class of Alzheimer's disease medications acting on the glutamatergic system by blocking NMDA glutamate receptors. Memantine is marketed under the brands Axura and Akatinol by Merz, Namenda by Forest, Ebixa and Abixa by Lundbeck and Memox by Unipharm. Adverse effects Memantine is generally well-tolerated .Common adverse drug reactions (≥1% of patients) include: confusion, dizziness, drowsiness, headache, insomnia, agitation, and/or hallucinations. Less common adverse effects include: vomiting, anxiety, hypertonia, cystitis, and increased libido. On the other hand; it has been reported to induce reversible neurological impairment in multiple sclerosis, that led to stop an ongoing clinical trial. Though exceedingly rare, extrapyramidal side effects (such as dystonic reactions, etc) may occur, particularly in the younger population. Slide 38: Pharmacology Glutamatergic (NMDA receptor) A dysfunction of glutamatergic neurotransmission, manifested as neuronal excitotoxicity, is hypothesized to be involved in the etiology of Alzheimer's disease. Targeting the glutamatergic system, specifically NMDA receptors, offers a novel approach to treatment in view of the limited efficacy of existing drugs targeting the cholinergic system. Memantine is a low-affinity voltage-dependent uncompetitive antagonist at glutamatergic NMDA receptors. By binding to the NMDA receptor with a higher affinity than Mg2+ions, memantine is able to inhibit the prolonged influx of Ca2+ ions which forms the basis of neuronal excitotoxicity. The low affinity and rapid off-rate kinetics of memantine at the level of the NMDA receptor-channel, however, preserves the physiological function of the receptor as it can still be activated by the relatively high concentrations of glutamate released following depolarization of the presynaptic neuron. The interaction of memantine with NMDA receptors plays a major role in the symptomatic improvement the drug produces in Alzheimer's disease. Moreover, there is no evidence as yet that the ability of memantine to protect against NMDA receptor-mediated excitotoxicity has a disease modifying effect in Alzheimer's, although this has been suggested in animal models. NMDA receptor antagonists ketamine and PCP have direct effects on the dopamine D2 and serotonin 5-HT2receptors¾implications for models of schizophrenia : NMDA receptor antagonists ketamine and PCP have direct effects on the dopamine D2 and serotonin 5-HT2receptors¾implications for models of schizophrenia Ketamine and PCP are commonly used as selective NMDA receptor antagonists to model the putative hypoglutamate state of schizophrenia and to test new antipsychotics. Recent findings question the NMDA receptor selectivity of these agents. To examine this further, we measured the affinity of ketamine and PCP for the high-affinity states of the dopamine D2 and serotonin 5-HT2 receptor and found that ketamine shows very similar affinity at the NMDA receptor and D2 sites with a slightly lower affinity for 5-HT2 (0.5 M, 0.5 M and 15 M respectively), while PCP shows similar affinity for the NMDA and 5-HT2 sites, with a slightly lower affinity for the D2 site (2 M, 5 M and 37 M respectively). Further, ketamine and PCP in clinically relevant doses caused a significant increase in the incorporation of [35S]GTP--S binding in CHO-cells expressing D2 receptors, which was prevented by raclopride, suggesting a partial agonist effect at the D2 receptor. Thus, ketamine and PCP may not produce a selective hypoglutamate state, but more likely produce a non-selective multi-system neurochemical perturbation via direct and indirect effects. These findings confound the inferences one can draw from the ketamine/PCP models of schizophrenia. NMDA receptor antagonists and limbic status epilepticus: a comparison with stand : NMDA receptor antagonists and limbic status epilepticus: a comparison with stand Status epilepticus (SE) evolves through several stages when untreated. The later stages of SE are less responsive to standard anticonvulsants and may require general anesthesia to suppress seizures. Antagonists acting at the N-methyl-D-aspartate (NMDA) subclass of glutamate (excitatory) receptors have been demonstrated to exert antiepileptic activity in some seizure models. We report experiments performed to determine if NMDA receptor antagonists are effective in stopping seizures in the late stages of SE. A model of limbic SE induced by 90 min of 'continuous' electrical stimulation of the hippocampus in rats was employed. Three NMDA receptor antagonists, one 'competitive' (CPP) and two 'non-competitive' (ketamine and MK-801), were compared to 3 standard antiepileptic drugs (diazepam, phenobarbital, and phenytoin) for their ability to suppress seizures at a physiologically defined stage of SE. All NMDA receptor antagonists, diazepam and phenobarbital were effective in suppressing behavioral and electrographic seizures for varying periods of time. Phenytoin had no effect on SE. Ketamine and MK-801 induced a paradoxical enhancement of electrographic seizures that preceded SE suppression. We believe that NMDA-receptor antagonists offer a novel approach for treating the late stages of SE. references : references RANG AND DALE’S PHARMACOLOGY; H P RANG,M M DALE,J M RITTER,R J FLOWER; SIXTH EDITION; CHURCHILL LIVINGSTONE ELSEVIER 2007; 479-492. GOODMAN & GILMAN’S THE PHARMACOLOGICAL BASIS OF THERAPEUTICS; J G HARDMAN,L E LIMBIRD;ELEVENTH EDITION;McGRAW-HILL 2006;308-309 You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
a bunty_jagiwala Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 437 Category: Science & Tech.. License: All Rights Reserved Like it (4) Dislike it (0) Added: October 10, 2009 This Presentation is Public Favorites: 2 Presentation Description No description available. Comments Posting comment... By: nayira (18 month(s) ago) This presentation is very informative. Please make it in a downloaded form or please send it to me Saving..... Post Reply Close Saving..... Edit Comment Close By: Meghapatel106 (18 month(s) ago) please send this to me..its very much informative Saving..... Post Reply Close Saving..... Edit Comment Close By: lamieess (19 month(s) ago) please i need this presentation please download it to me Saving..... Post Reply Close Saving..... Edit Comment Close By: raj_patel (23 month(s) ago) Hi this presentation is very informative. Please make it downloaded form. Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript MOLECULAR PHARMACOLOGYA SEMINAR ON NMDA RECEPTORS(NMDA=N-methyl D-aspartate) : MOLECULAR PHARMACOLOGYA SEMINAR ON NMDA RECEPTORS(NMDA=N-methyl D-aspartate) GUIDED BY:- PRESENTED BY:- Mrs. Versha J. Galani Biren H. Shah M.Pharm (Ph.’cology) 09PLY02 (SEM.-1) INTRODUCTION : INTRODUCTION What is receptor? it is defined as a specific binding site with functional correlate(s). what is neurotransmitter? It is a substance released by a neuron, acting rapidly, briefly and at short range on the membrane of adjacent neuron, producing a change in conductance which either increase or decreases the excitability of the post syneptic cell. NEUROTRANSMITTERS IN CNS : NEUROTRANSMITTERS IN CNS Noradrenaline Dopamine Serotonin Acetylcholine AMINO ACID TRANSMITTERS GABA Glutamate Aspartate Glycine TYPES OF AMINO ACID TRANSMITTERS : TYPES OF AMINO ACID TRANSMITTERS EXCITATORY AMINO-ACIDS AS CNS TRANSMITTERS : EXCITATORY AMINO-ACIDS AS CNS TRANSMITTERS Unravelling some of the complexities of amino acids reeptors and signalling mechanisms has thrown considerable light on their role in brain function and their likely involvement in CNS disease. L-Glutamate is the principal and ubiquitous excitatory transmitter in the CNS. Aspartate Plays excitatory role in certain brain regions and homocysteate. This role of aspartate is controversial. Function of glutamate : Function of glutamate Is the most prominent neurotrnsmitter in the body being present in over 50% of the nervous tissues. Glutamate was initially discovered to be a neurotransmitter following insect studies in the early1960s. The primary glutamae receptor is specifically sensitive to NMDA,which cause direct action of the central pore of the receptor,an ion channel, to drive the neuron to depolarize. Depolarization will trigger the primary firing or actio potential of the neuron,therefore NMDA is excitation. METABOLISM OF TRANSMITTER AMINO ACIDS IN THE BRAIN.Transmitter substances are marked with green boxes.gaba-t=gaba transaminase,gad=glutamic acid decarboxylase : METABOLISM OF TRANSMITTER AMINO ACIDS IN THE BRAIN.Transmitter substances are marked with green boxes.gaba-t=gaba transaminase,gad=glutamic acid decarboxylase METABOLISM & release of AMINO ACIDS IN THE BRAIN : METABOLISM & release of AMINO ACIDS IN THE BRAIN Glutamate is widely & fairly uniformly distributed in the CNS. Glutamate in the CNS comes mainly from eiher glucose,via the crebs cycle,or glutamine, which is synthesized by glial cells & taken up by the neurons. The metabolic & neurotransmitter pools being linked by transaminase enzyme that catalyze the interconversion of glutamate & α-oxoglutarate There is interconnection between the pathways for the synthesis of EEAs & inhibitory amino acids (GABA &Glycine).s Transport of glutamate (glu)and glutamine(gln) by neurons and astrocytes.Eaat=excitatory amino acid transporter,GlnT=glutamine transporter : Transport of glutamate (glu)and glutamine(gln) by neurons and astrocytes.Eaat=excitatory amino acid transporter,GlnT=glutamine transporter Transport & release of glutamate &glycine : Transport & release of glutamate &glycine Glutamate is stored in synaptic vesicles and released by Ca+2 dependent exocytosis. specific transporter proteins account for its uptake by neurons and other cells. Released glutamate is taken up by cells in exchange for Na and transported driven by the proton gradient across the vesicles membrane. Many drugs(not in clinical use)are known that interfere specifically with glutamate. The action of glutamate is terminated mainly by carrier-mediated reuptake into the nerve terminals and neighboring astrocytes. This transport can, under some circumstances operate in reverse and constitute a source of glutamate release, a process that may occur under pathological condition such as brain ischemia. Function of glutamate : Function of glutamate Is the most prominent neurotrnsmitter in the body being present in over 50% of the nervous tissues. Glutamate was initially discovered to be a neurotransmitter following insect studies in the early1960s. The primary glutamae receptor is specifically sensitive to NMDA,which cause direct action of the central pore of the receptor,an ion channel, to drive the neuron to depolarize. Depolarization will trigger the primary firing or actio potential of the neuron,therefore NMDA is excitation. Slide 12: The NMDA receptor (NMDAR), a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function. The NMDAR is a specific type of ionotropic glutamate receptor. NMDA (N-methyl D-aspartate) is the name of a selective agonist that binds to NMDA receptors but not to other glutamate receptors. Activation of NMDA receptors results in the opening of an ion channel that is nonselective to cations. A unique property of the NMDA receptor is its voltage-dependent activation, a result of ion channel block by extracellular Mg2+ ions. This allows voltage-dependent flow of Na+ and small amounts of Ca2+ ions intoThe NMDA receptor (NMDAR), a glutamate receptor, is the predominant molecular device for controlling synaptic plasticity and memory function Slide 13: The NMDAR is a specific type of ionotropic glutamate receptor. NMDA (N-methyl D-aspartate) is the name of a selective agonist that binds to NMDA receptors but not to other the cell and K+ out of the cell. Calcium flux through NMDARs is thought to play a critical role in synaptic plasticity, a cellular mechanism for learning and memory. The NMDA receptor is distinct in two ways: First, it is both ligand-gated and voltage-dependent; second, it requires co-activation by two ligands - glutamate and glycine. Types of glutamate receptors : Types of glutamate receptors Can be divided in to two groups according to the mechanism by which their activation gives rise to a postsynaptic current. Ionotropic glutamate receptors from the ion channel pore that activates when glutamate binds to the receptor. Metabotropic glutamate receptors indirectly activate ion-channels on the plasma membrane through a signaling cascade that involves G-protein. Pharmacology of nmda receptors : Pharmacology of nmda receptors Slide 17: Molecular Biology Two major subunit families designated NR1, NR2 as well as a modulatory subunit designated NR3 have been cloned. Most functional receptors in the mammalian CNS are formed by combination of NR1 and NR2 subunits which express the glycine and glutamate recognition sites respectively. NR1 Subunits Alternative splicing generates eight isoforms for the NR1 subfamily . The variants arise from splicing at three exons one encodes a 21-amino acid insert in the N-terminal domain (N1, exon 5), and two encode adjacent sequences of 37 and 38 amino acids in the C-terminal domain (C1, exon 21 and C2, exon 22). NR1 variants are sometimes denoted by the presence or absence of these three alternatively spliced exons (from N to C1 to C2). NR1111 has all three exons, NR1000 has none, and NR1100 has only the N-terminal exon. The variants from NR1000 to NR1111 are alternatively denoted as NMDAR1E, C, D, A, G, F, “H” and B respectively or NMDAR1-4a,-2a,-3a,-1a,-4b,-2b,-3b and-1b respectively, but the more frequent terminology using non-capitalized suffices for the most common splice variants is NR1a (NR1011 or NMDAR1A) and NR1b (NR1100 or NMDARIG). MRNA for double splice variants in the C1/C2 regions such as NR1011 (NR1a) show an almost complementary pattern to those lacking both of these inserts such as as Nr2 subunite : Nr2 subunite Slide 19: NR2 Subunits The NR2 subfamily consists of four individual subunits, NR2A to NR2D. Various heteromeric NMDA receptor channels formed by combinations of NR1 and NR2 subunits are known to differ in gating properties, Mg2+ sensitivity and pharmacological profile (Sucher et al., 1996). The heteromeric assembly of NR1 and NR2C subunits for instance, has a lower sensitivity to Mg2+ but increased sensitivity to glycine and a very restricted distribution in the brain. In situ hybridization has revealed overlapping but different expression for NR2 mRNA e.g. NR2A mRNA is distributed ubiquitously like NR1 with highest densities occurring in hippocampal regions and NR2B is expressed predominantly in forebrain but not in cerebellum where NR2C predominates. The spinal cord expresses high levels of NR2C and NR2D (Tolle et al., 1993) and these may form heteroligomeric receptors with NR1 plus NR2A which would provide a basis for the development of drugs selectively aimed at spinal cord disorders(Sundstrom et al., 1997). NMDA receptors cloned from murine CNS have a different terminology to those in the rat: z1 remains the terminology for the mouse equivalent of NR1 and e1 to e4 represent NR2A to 2D subunits respectively. Slide 20: NR3 Subunits NR3 (NRL or Chi-1) is expressed predominantly in the developing CNS and does not seem to form functional homomeric glutamate-activated channels but co-expression of NR3 with NR1 plus NR2 subunits decreases response magnitude (Sucher et al., 1995; Kinsley et al., 1999; Matsuda et al., 2002). However, NR3A or NR3B do co-assemble with NR1 alone in Xenopus oocytes to form excitatory glycine receptors that are unaffected by glutamate or NMDA, Ca2+-impermeable, resistant to blockade by Mg2+ uncompetitive and competitive antagonists and actually inhibited by the glycine co-agonist D-serine. (Chatterton et al., 2002) Special features of nmda receptors : Special features of nmda receptors They are highly permeable to ca,as well as to other cations,so activation of NMDA receptors is particularly effctivein promoting ca entry. They are readily blocked by Mg,and this block shows marked voltage dependence.it occures at physiological Mg concentration if the cell is depoarised. Aaaactivation of NMDA receptors requires glycine as well as glutamate.the binding site for glycine is distinct from the glutamate binding site,and both have to be occupied for the channel to open. Facillation of Nmda by glycine : Facillation of Nmda by glycine Slide 23: Agonists Activation of NMDA receptors requires binding of glutamate or aspartate (aspartate does not stimulate the receptors as strongly). In addition, NMDARs also require the binding of the co-agonist glycine for the efficient opening of the ion channel, which is a part of this receptor. D-serine has also been found to co-agonize the NMDA receptor with even greater potency than glycine. D-serine is produced by serine racemase, and is enriched in the same areas as NMDA receptors. Removal of D-serine can block NMDA-mediated excitatory neurotransmission in many areas. Recently, it has been shown that D-serine is synthesized mostly by neurons, indicating a role for neuron-derived D-serine in NMDA receptor regulation. Main site of drug action nmda : Main site of drug action nmda Mechanism of action : Mechanism of action The NMDA receptor is an ionotropic receptor that allows for the transfer of electrical signals between neurons in the brain and in the spinal column. For electrical signals to pass, the NMDA receptor must be open. To remain open, an NMDA receptor must bind to glutamate and to glycine. An NMDA receptor that is bound to glycine and glutamate and has an open ion channel is called "activated." Chemicals that deactivate the NMDA receptor are called antagonists. NMDAR antagonists fall into four categories: Competitive antagonists, which bind to and block the binding site of the neurotransmitter glutamate; glycine antagonists, which bind to and block the glycine site; noncompetitive antagonists, which inhibit NMDARs by binding to allosteric sites; and uncompetitive antagonists, which block the ion channel by binding to a site within it. examples : examples Competitive antagonists AP5P (APV, R-2-amino-5-phosphonopentanoate) AP7 (2-amino-7-phosphonoheptanoic acid) CPPene (3-[(R)-2-carboxypiperazin-4-yl]-prop-2-enyl-1-phosphonic acid) Uncompetitive channel blockers Amantadine: used for treating Parkinson's diseases and influenza and Alzhiemer's. Dextromethorphan: a common antitussive found in cough medicines. Dextrorphan: active metabolite of dextromethorphan. Schedule I in the US. Ibogaine: a Schedule I controlled substance in the United States. Ketamine: an animal and human anesthetic and recreational drug. Slide 28: Memantine: moderate affinity, voltage-dependent uncompetitive antagonist. Approved in the U.S. by the Food and Drug Administration for the treatment of Alzheimer's disease. Nitrous oxide: used for anesthesia, particularly in dentistry. Phencyclidine: a Schedule II controlled substance in the United States. Riluzole: used to treat amyotrophic lateral sclerosis. Tiletamine: an animal anesthetic. Non-competitive antagonists Aptiganel (Cerestat, CNS-1102): binds the Mg2+ binding site within the channel of the NMDA receptor. Dizocilpine (MK-801): an experimental drug. HU-211: an enantiomer of the potent cannabinoid HU-210 which lacks cannabinoid effects and instead acts as a potent non-competitive NMDA antagonist. Remacemide: principle metabolite is an uncompetitive antagonist with a low affinity for the binding site. Glycine antagonists These drugs act at the glycine binding site: 1-Aminocyclopropanecarboxylic acid (ACPC) 7-Chlorokynurenate DCKA (5,7-dichlorokynurenic acid) Kynurenic acid: a naturally occurring antagonist Lacosamide: an investigational drug for the treatment of epilepsy and diabetic neuropathic pain. Mechanism of long term potentiation : Mechanism of long term potentiation A With infrequent synaptic activity, glutamate activates mainly AMPA-receptors. There is insufficient glutamate to activate metabotropic (met) receptors, and NMDA-receptor channels are blocked by Mg2+. B After a conditioning train of stimuli, enough glutamate is released to activate metabotropic receptors, and NMDA channels are unblocked by the sustained depolarisation. The resulting increase in [Ca2+]i activates PKC and NOS. PKC phosphorylates various proteins, including AMPA-receptors (causing facilitation of transmitter action) and other signal transduction molecules controlling gene transcription (not shown) in the postsynaptic cell. Release of NO facilitates glutamate release (retrograde signalling, otherwise known as NO turning back). (G, glutamate; NMDA, N-methyl-d-aspartate; AMPA, α-amino-3-hydroxy-5-methylisoxazole; PI, phosphatidylinositol; IP3, inositol 1,4,5-trisphosphate; DAG, diacylglycerol; PKC, protein kinase; NO, nitric oxide; NOS, nitric oxide synthase.) Slide 32: NMDA antagonists prevent LTP, without affecting normal, non-potentiated transmission (which depends on AMPA-receptors). Disruption of the gene for the NMDA-receptor has the same effect. LTP occurs only if the postsynaptic cell is depolarised at the time when the conditioning burst of stimulation is delivered. Blocking AMPA-receptors prevents this and prevents LTP. Antagonists at metabotropic glutamate receptors reduce the duration of LTP; LTP is also impaired in transgenic mice lacking the mGluR1 receptor. Calcium entry into the postsynaptic cell is required, and there is evidence that activation of protein kinase C , resulting in phosphorylation of AMPA-receptors, is involved in the mechanism of potentiation. LTP is reduced by agents that block the synthesis or effects of nitric oxide or arachidonic acid. One or both of these mediators may be the hitherto elusive 'retrograde messenger' through which events in the postsynaptic cell are able to influence the presynaptic nerve terminal Alzheimer's disease Misprocessing of amyloid precursor protein (APP) in Alzheimer's disease disrupts LTP and is thought to lead to early cognitive decline in individuals with the disease. LTP has received much attention among those who study Alzheimer's disease (AD), a neurodegenerative disease that causes marked cognitive decline and dementia. Much of this deterioration occurs in association with degenerative changes in the hippocampus and other medial temporal lobe structures. Because of the hippocampus' well established role in LTP, some have suggested that the cognitive decline seen in individuals with AD may result from impaired LTP. Glutamate excitotoxicity : Glutamate excitotoxicity Slide 34: Glutamate Excitotoxicity High concentrations of glutamate produce neuronal cell death . Initially, the cascade of events leading to neuronal death was thought to be triggered exclusively by excessive activation of NMDA or AMPA/kainate receptors, allowing significant influx of Ca2+ into the neurons. Such glutamate neurotoxicity was thought to underlie the damage that occurs after ischemia or hypoglycemia in the brain, during which a massive release and impaired reuptake of glutamate in the synapse would lead to excess stimulation of glutamate receptors and subsequent cell death. Although NMDA receptor antagonists can attenuate neuronal cell death induced by activation of these receptors , even the most potent antagonists cannot prevent all such damage, causing additional efforts to salvage the therapeutic potential for glutamate antagonists as neuroprotectants. More recent studies implicate both local depletion of Na+ and K+, as well as small but significant elevations of extracellular Zn2+ as factors that can activate both necrotic and pro-apoptotic cascades, leading to neuronal death. Because of the widespread distribution of glutamate receptors in the CNS, they have become targets for diverse therapeutic interventions. For example, a role for disordered glutamatergic transmission in the etiology of chronic neurodegenerative diseases and in schizophrenia has been postulated. Uses and effects : Uses and effects NMDA receptor antagonists induce a state called dissociative anesthesia, marked by catalepsy, amnesia and analgesia. Ketamine and other NMDA receptor antagonists are most frequently used in conjunction with diazepam as anesthesia in cosmetic or reconstructive plastic surgery and in the treatment of burn victims. Ketamine is a favored anesthetic for emergency patients with unknown medical history because it depresses breathing and circulation less than other anesthetics. The NMDA receptor antagonist dextromethorphan is one of the most commonly used cough suppressants in the world. Slide 36: Depressed NMDA receptor function is associated with an array of negative symptoms. For example, NMDA receptor hypofunction that occurs as the brain ages may be partially responsible for memory deficits associated with aging. Schizophrenia may also have to do with irregular NMDA receptor function (the "glutamate hypothesis" of schizophrenia). Increased levels of another NMDA antagonist, kynurenic acid, may aggravate the symptoms of schizophrenia, according to the "kynurenic hypothesis". NMDA receptor antagonists can mimic these problems; they sometimes induce "psychotomimetic" side effects, symptoms resembling psychosis. Such side effects caused by NMDA receptor inhibitors include hallucinations, paranoid delusions, confusion, difficulty concentrating, agitation, alterations in mood, nightmares, catatonia, ataxia, anaesthesia, and learning and memory deficits. Because of these psychotomimetic effects, NMDA receptor antagonists, especially phencyclidine, ketamine, and dextromethorphan, are used as recreational drugs. At subanesthetic doses, these drugs have mild stimulant effects, and at higher doses, begin inducing dissociation and hallucinations. Most NMDA receptor antagonists are metabolized in the liver. Frequent administration of most NMDA receptor antagonists can lead to tolerance, whereby the liver will more quickly eliminate NMDA receptor antagonists from the bloodstream. Role of nmda antagonists in treatment of alzheimer’s disease : Role of nmda antagonists in treatment of alzheimer’s disease Memantine is the first in a novel class of Alzheimer's disease medications acting on the glutamatergic system by blocking NMDA glutamate receptors. Memantine is marketed under the brands Axura and Akatinol by Merz, Namenda by Forest, Ebixa and Abixa by Lundbeck and Memox by Unipharm. Adverse effects Memantine is generally well-tolerated .Common adverse drug reactions (≥1% of patients) include: confusion, dizziness, drowsiness, headache, insomnia, agitation, and/or hallucinations. Less common adverse effects include: vomiting, anxiety, hypertonia, cystitis, and increased libido. On the other hand; it has been reported to induce reversible neurological impairment in multiple sclerosis, that led to stop an ongoing clinical trial. Though exceedingly rare, extrapyramidal side effects (such as dystonic reactions, etc) may occur, particularly in the younger population. Slide 38: Pharmacology Glutamatergic (NMDA receptor) A dysfunction of glutamatergic neurotransmission, manifested as neuronal excitotoxicity, is hypothesized to be involved in the etiology of Alzheimer's disease. Targeting the glutamatergic system, specifically NMDA receptors, offers a novel approach to treatment in view of the limited efficacy of existing drugs targeting the cholinergic system. Memantine is a low-affinity voltage-dependent uncompetitive antagonist at glutamatergic NMDA receptors. By binding to the NMDA receptor with a higher affinity than Mg2+ions, memantine is able to inhibit the prolonged influx of Ca2+ ions which forms the basis of neuronal excitotoxicity. The low affinity and rapid off-rate kinetics of memantine at the level of the NMDA receptor-channel, however, preserves the physiological function of the receptor as it can still be activated by the relatively high concentrations of glutamate released following depolarization of the presynaptic neuron. The interaction of memantine with NMDA receptors plays a major role in the symptomatic improvement the drug produces in Alzheimer's disease. Moreover, there is no evidence as yet that the ability of memantine to protect against NMDA receptor-mediated excitotoxicity has a disease modifying effect in Alzheimer's, although this has been suggested in animal models. NMDA receptor antagonists ketamine and PCP have direct effects on the dopamine D2 and serotonin 5-HT2receptors¾implications for models of schizophrenia : NMDA receptor antagonists ketamine and PCP have direct effects on the dopamine D2 and serotonin 5-HT2receptors¾implications for models of schizophrenia Ketamine and PCP are commonly used as selective NMDA receptor antagonists to model the putative hypoglutamate state of schizophrenia and to test new antipsychotics. Recent findings question the NMDA receptor selectivity of these agents. To examine this further, we measured the affinity of ketamine and PCP for the high-affinity states of the dopamine D2 and serotonin 5-HT2 receptor and found that ketamine shows very similar affinity at the NMDA receptor and D2 sites with a slightly lower affinity for 5-HT2 (0.5 M, 0.5 M and 15 M respectively), while PCP shows similar affinity for the NMDA and 5-HT2 sites, with a slightly lower affinity for the D2 site (2 M, 5 M and 37 M respectively). Further, ketamine and PCP in clinically relevant doses caused a significant increase in the incorporation of [35S]GTP--S binding in CHO-cells expressing D2 receptors, which was prevented by raclopride, suggesting a partial agonist effect at the D2 receptor. Thus, ketamine and PCP may not produce a selective hypoglutamate state, but more likely produce a non-selective multi-system neurochemical perturbation via direct and indirect effects. These findings confound the inferences one can draw from the ketamine/PCP models of schizophrenia. NMDA receptor antagonists and limbic status epilepticus: a comparison with stand : NMDA receptor antagonists and limbic status epilepticus: a comparison with stand Status epilepticus (SE) evolves through several stages when untreated. The later stages of SE are less responsive to standard anticonvulsants and may require general anesthesia to suppress seizures. Antagonists acting at the N-methyl-D-aspartate (NMDA) subclass of glutamate (excitatory) receptors have been demonstrated to exert antiepileptic activity in some seizure models. We report experiments performed to determine if NMDA receptor antagonists are effective in stopping seizures in the late stages of SE. A model of limbic SE induced by 90 min of 'continuous' electrical stimulation of the hippocampus in rats was employed. Three NMDA receptor antagonists, one 'competitive' (CPP) and two 'non-competitive' (ketamine and MK-801), were compared to 3 standard antiepileptic drugs (diazepam, phenobarbital, and phenytoin) for their ability to suppress seizures at a physiologically defined stage of SE. All NMDA receptor antagonists, diazepam and phenobarbital were effective in suppressing behavioral and electrographic seizures for varying periods of time. Phenytoin had no effect on SE. Ketamine and MK-801 induced a paradoxical enhancement of electrographic seizures that preceded SE suppression. We believe that NMDA-receptor antagonists offer a novel approach for treating the late stages of SE. references : references RANG AND DALE’S PHARMACOLOGY; H P RANG,M M DALE,J M RITTER,R J FLOWER; SIXTH EDITION; CHURCHILL LIVINGSTONE ELSEVIER 2007; 479-492. GOODMAN & GILMAN’S THE PHARMACOLOGICAL BASIS OF THERAPEUTICS; J G HARDMAN,L E LIMBIRD;ELEVENTH EDITION;McGRAW-HILL 2006;308-309