Methoctramine Synthesis Essay
Initial Ca2+-dependent contraction of the intestinal smooth muscle mediated by Gq-coupled receptors is attenuated by RGS4 (regulator of G-protein signalling 4). Treatment of colonic muscle cells with IL-1β (interleukin-1β) inhibits acetylcholine-stimulated initial contraction through increasing the expression of RGS4. NF-κB (nuclear factor κB) signalling is the dominant pathway activated by IL-1β. In the present study we show that RGS4 is a new target gene regulated by IL-1β/NF-κB signalling. Exposure of cultured rabbit colonic muscle cells to IL-1β induced a rapid increase in RGS4 mRNA expression, which was abolished by pretreatment with a transcription inhibitor, actinomycin D, implying a transcription-dependent mechanism. Existence of the canonical IKK2 [IκB (inhibitor of NF-κB) kinase 2]/IκBα pathway of NF-κB activation induced by IL-1β in rabbit colonic muscle cells was validated with multiple approaches, including the induction of reporter luciferase activity and endogenous NF-κB-target gene expression, NF-κB-DNA binding activity, p65 nuclear translocation, IκBα degradation and the phosphorylation of IKK2 at Ser177/181 and p65 at Ser536. RGS4 up-regulation by IL-1β was blocked by selective inhibitors of IKK2, IκBα or NF-κB activation, by effective siRNA (small interfering RNA) of IKK2, and in cells expressing either the kinase-inactive IKK2 mutant (K44A) or the phosphorylation-deficient IκBα mutant (S32A/S36A). An IKK2-specific inhibitor or effective siRNA prevented IL-1β-induced inhibition of acetylcholine-stimulated PLC-β (phopsholipase C-β) activation. These results suggest that the canonical IKK2/IκBα pathway of NF-κB activation mediates the up-regulation of RGS4 expression in response to IL-1β and contributes to the inhibitory effect of IL-1β on acetylcholine-stimulated PLC-β-dependent initial contraction in rabbit colonic smooth muscle.
Abbreviations: ACh, acetylcholine; APQ, 6-amino-4-(4-phenoxyphenylethylamino)quinazoline; COX-2, cyclo-oxygenase 2; EGFP, enhanced green fluorescent protein; EMSA, electrophoretic mobility-shift assay; FBS, foetal bovine serum; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HA, haemagglutinin; IBD, inflammatory bowel disease; ICAM, intercellular adhesion molecule; IκB, inhibitor of nuclear factor κB; IKK, IκB kinase; IKK2-IV, IKK2 inhibitor IV; IL, interleukin; LPS, lipopolysaccharide; MG132, carbobenzoxy-L-leucyl-L-leucyl-L-leucinal Z-LLL-CHO; MMP, matrix metalloproteinase; NF-κB, nuclear factor κB; PLC, phospholipase C; RGS, regulator of G-protein signalling; RT, reverse transcription; siRNA, small interfering RNA; TNFα, tumour necrosis factor α
- © The Authors Journal compilation © 2008 Biochemical Society
Presentation on theme: "Introduction to CNS pharmacology"— Presentation transcript:
1 Introduction to CNS pharmacology
ByS.Bohlooli, PhDSchool of Medicine, Ardabil University of Medical Sciences
2 Ion channels & neurotransmitter receptors
Voltage gated channelsLigand gated channelsIonotropic receptorsMetabotropic receptorsMembrane delimitedDiffusible second messenger
3 Figure Types of ion channels and neurotransmitter receptors in the CNS. A shows a voltage-gated channel in which a voltage sensor component of the protein controls the gating (broken arrow) of the channel. B shows a ligand-gated channel in which the binding of the neurotransmitter to the ionotropic channel receptor controls the gating (broken arrow) of the channel. C shows a G protein-coupled (metabotropic) receptor, which when bound, activates a G protein that then interacts directly with an ion channel. D shows a G protein-coupled receptor, which when bound, activates a G protein that then activates an enzyme. The activated enzyme generates a diffusible second messenger, eg, cAMP, which interacts with an ion channel.
4 Nicotinic acetylcholine receptor
Figure The adult nicotinic acetylcholine receptor (nAChR) is an intrinsic membrane protein with five distinct subunits (a2bdg) A: Cartoon of the one of five subunits of the AChR in the end plate surface of adult mammalian muscle. Each subunit contains four helical domains labeled M1 to M4. The M2 domains line the channel pore. B: Cartoon of the full AChR. The N termini of two subunits cooperate to form two distinct binding pockets for acetylcholine (ACh). These pockets occur at the a-b and the d-a subunit interfaces.
5 The synapse & synaptic potentials
ExcitatoryExcitatory post-synaptic potential (EPSP)Ionotropic receptorInhibitoryInhibitory post-synaptic potential (IPSP)Presynaptic inhibition
6 (+/-) Show / Hide Bibliography
Table Some toxins used to characterize ion channels.Channel TypesMode of Toxin ActionSourceVoltage-gatedSodium channelsTetrodotoxin (TTX)Blocks channel from outsidePuffer fishBatrachotoxin (BTX)Slows inactivation, shifts activationColombian frogPotassium channelsApaminBlocks "small Ca-activated" K channelHoneybeeCharybdotoxinBlocks "big Ca-activated" K channelScorpionCalcium channelsOmega conotoxin (w-CTX-GVIA)Blocks N-type channelPacific cone snailAgatoxin (w-AGA-IVA)Blocks P-type channelFunnel web spiderLigand-gatedNicotinic ACh receptora-BungarotoxinIrreversible antagonistMarine snakeGABAA receptorPicrotoxinBlocks channelSouth Pacific plantGlycine receptorStrychnineCompetitive antagonistIndian plantAMPA receptorPhilanthotoxinWaspCopyright © 2007 by The McGraw-Hill Companies, Inc. All rights reserved.(+/-) Show / Hide BibliographySend Feedback Customer ServiceTitle Updates User Responsibilities Training Center What's NewTeton Server (4.5.0) - ©2006 Teton Data Systems Send Us Your Comments
7 Figure 21-2. Excitatory synaptic potentials and spike generation
Figure Excitatory synaptic potentials and spike generation. The figure shows entry of a microelectrode into a postsynaptic cell and subsequent recording of a resting membrane potential of -70 mV. Stimulation of an excitatory pathway (E) generates transient depolarization. Increasing the stimulus strength (second E) increases the size of the depolarization, so that the threshold for spike generation is reached.
8 Figure 21-3. Interaction of excitatory and inhibitory synapses
Figure Interaction of excitatory and inhibitory synapses. On the left, a suprathreshold stimulus is given to an excitatory pathway (E) and an action potential is evoked. On the right, this same stimulus is given shortly after activating an inhibitory pathway (I), which results in an inhibitory postsynaptic potential (IPSP) that prevents the excitatory potential from reaching threshold.
9 Site of drug actionFigure Sites of drug action. Schematic drawing of steps at which drugs can alter synaptic transmission. (1) Action potential in presynaptic fiber; (2) synthesis of transmitter; (3) storage; (4) metabolism; (5) release; (6) reuptake; (7) degradation; (8) receptor for the transmitter; (9) receptor-induced increase or decrease in ionic conductance.
10 Identification of central neurotransmitters
More difficult for CNSAnatomic complexityLimitation of available techniques
11 Criteria for neurotransmitter identification
LocalizationMicrocytochemicalimmonocytochemicalReleaseSimulation of Brain slicesCalcium dependency of releaseSynaptic mimicryMicroiontophoresisPhysiological viewPharmacological view
12 Cellular organization of the brain
Hierarchical systemsSensory perception, motor controlPhasic information, delineated pathwaysTwo types of neuronsProjection or relayLocal circuit neuronsLimited number of transmittersNonspecific or diffuse neuronal systemsAffecting global function of CNSSmall number of neurons, projections to wide area of CNS
13 Figure 21-5. Pathways in the central nervous system
Figure Pathways in the central nervous system. A shows parts of three relay neurons (color) and two types of inhibitory pathways, recurrent and feed-forward. The inhibitory neurons are shown in gray. B shows the pathway responsible for presynaptic inhibition in which the axon of an inhibitory neuron (gray) synapses on the axon terminal of an excitatory fiber (color).
14 Central neurotransmitters
Amino acidsNeutral amino acidsAcidic amino acidsAcetylcholineMonoaminesDopamineNorepinephrine5-hydroxytryptaminePeptidesNitric oxideendocananbiniods
15 Receptor Subtypes and Preferred Agonists
Table Summary of neurotransmitter pharmacology in the central nervous system. (Many other central transmitters have been identified [see text].)TransmitterAnatomyReceptor Subtypes and Preferred AgonistsReceptor AntagonistsMechanismsAcetylcholineCell bodies at all levels; long and short connectionsMuscarinic (M1): muscarinePirenzepine, atropineExcitatory: ¯ in K+ conductance; ↑ IP3, DAGMuscarinic (M2): muscarine, bethanecholAtropine, methoctramineInhibitory: ↑ K+ conductance; ¯ cAMPMotoneuron-Renshaw cell synapseNicotinic: nicotineDihydro-b-erythroidine, a-bungarotoxinExcitatory: ↑ cation conductance
16 TransmitterAnatomyReceptor Subtypes and Preferred AgonistsReceptor AntagonistsMechanismsDopamineCell bodies at all levels; short, medium, and long connectionsD1 PhenothiazinesInhibitory (?): cAMPD2: bromocriptine Phenothiazines, butyrophenonesInhibitory (presynaptic): Ca2+; Inhibitory (postsynaptic): in K+ conductance, cAMP GABASupraspinal and spinal interneurons involved in pre- and postsynaptic inhibitionGABAA: muscimol Bicuculline, picrotoxinInhibitory: Cl–conductance GABAB: baclofen 2-OH saclofenInhibitory (presynaptic): Ca2+ conductance; Inhibitory (postsynaptic): K+ conductance
17 TransmitterAnatomyReceptor Subtypes and Preferred AgonistsReceptor AntagonistsMechanismsGlutamateRelay neurons at all levels and some interneuronsN-Methyl-D-aspartate (NMDA): NMDA 2-Amino-5-phosphonovalerate, dizocilpineExcitatory: cation conductance, particularly Ca2+ AMPA: AMPACNQXExcitatory: cation conductanceKainate: kainic acid, domoic acidMetabotropic: ACPD, quisqualateMCPGInhibitory (presynaptic): Ca2+ conductance cAMP; Excitatory: K+ conductance, IP3, DAG GlycineSpinal interneurons and some brain stem interneuronsTaurine, -alanineStrychnineInhibitory: Cl–conductance
18 TransmitterAnatomyReceptor Subtypes and Preferred AgonistsReceptor AntagonistsMechanisms5-Hydroxytryptamine (serotonin)Cell bodies in midbrain and pons project to all levels5-HT1A: LSD Metergoline, spiperoneInhibitory: K+ conductance, cAMP 5-HT2A: LSD KetanserinExcitatory: K+ conductance, IP3, DAG 5-HT3: 2-methyl-5-HT OndansetronExcitatory: cation conductance5-HT4 Excitatory: K+ conductance
19 TransmitterAnatomyReceptor Subtypes and Preferred AgonistsReceptor AntagonistsMechanismsNorepinephrineCell bodies in pons and brain stem project to all levels1: phenylephrine PrazosinExcitatory: K+ conductance, IP3, DAG 2: clonidine YohimbineInhibitory (presynaptic): Ca2+ conductance; Inhibitory: K+ conductance, cAMP 1: isoproterenol, dobutamine Atenolol, practololExcitatory: K+ conductance, cAMP 2: albuterol ButoxamineInhibitory: may involve in electrogenic sodium pump; cAMP
20 TransmitterAnatomyReceptor Subtypes and Preferred AgonistsReceptor AntagonistsMechanismsHistamineCells in ventral posterior hypothalamusH1: 2(m-fluorophenyl)-histamine MepyramineExcitatory: K+ conductance, IP3, DAG H2: dimaprit RanitidineExcitatory: K+ conductance, cAMP H3: R--methyl-histamine ThioperamideInhibitory autoreceptors
21 TransmitterAnatomyReceptor Subtypes and Preferred AgonistsReceptor AntagonistsMechanismsOpioid peptidesCell bodies at all levels; long and short connectionsMu: bendorphinNaloxoneInhibitory (presynaptic): Ca2+ conductance, cAMP Delta: enkephalinInhibitory (postsynaptic): K+ conductance, cAMP Kappa: dynorphinTachykinins Primary sensory neurons, cell bodies at all levels; long and short connectionsNK1: Substance P methylester, aprepitantAprepitant Excitatory: K+ conductance, IP3, DAG NK2NK3EndocannabinoidsWidely distributedCB1: Anandamide, 2-arachidonyglycerolRimonabant
22 Schematic diagram of a glutamate synapse
Schematic diagram of a glutamate synapse. Glutamine is imported into the glutamatergic neuron (A) and converted into glutamate by glutaminase. The glutamate is then concentrated in vesicles by the vesicular glutamate transporter. Upon release into the synapse, glutamate can interact with AMPA and NMDA ionotropic receptor channels (AMPAR, NMDAR) in the postsynaptic density (PSD) and with metabotropic receptors (MGluR) on the postsynaptic cell (B). Synaptic transmission is terminated by active transport of the glutamate into a neighboring glial cell (C) by a glutamate transporter. It is synthesized into glutamine by glutamine synthetase and exported into the glutamatergic axon. (D) shows a model NMDA receptor channel complex consisting of a tetrameric protein that becomes permeable to Na+ and Ca2+ when it binds a glutamate molecule.