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Case 3-PBL Neurotransmitters Dopamine Parkinson´s disease
FIGURE 12-9: Cell-surface receptors utilize four distinct molecular mechanisms for transmembrane signaling. I. Ligand-gated ion channels. II. Receptors which possess intrinsic guanylyl cyclase activity. III. Receptors with intrinsic or associated tyrosine kinase activity. IV. G-protein-coupled receptors, which are linked to the opening/closing of ion channels, modulation of adenylyl cyclase and phosphoinositidespecific phospholipase C activities. SH2, Src homology 2 domain.
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
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FIGURE 12-1: Depolarization opens voltage-sensitive Ca2+ channels in the presynaptic nerve terminal (1). The influx of Ca2+ and the resulting high Ca2+ concentrations at active zones on the plasmalemma trigger (2) the exocytosis of small synaptic vesicles that store neurotransmitter (NT) involved in fast neurotransmission. Released neurotransmitter interacts with receptors in the postsynaptic membrane that either couple directly with ion channels (3) orCopyright act through second messengers, such as (4) G-protein–coupled receptors. © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved. Neurotransmitter receptors, also in the presynaptic nerve terminal membrane (5), either
FIGURE 12-3: Synaptic membrane structure. (A) Entire frog neuromuscular junction (NMJ, left) and longitudinal section through a portion of the nerve terminal (right). Arrows indicate planes of cleavage during freeze-fracture. (B) Three-dimensional view of presynaptic and postsynaptic membranes with active zones and immediately adjacent rows of synaptic vesicles. Plasma membranes are split along planes indicated by the arrows in A to illustrate structures observed by freeze-fracture. The cytoplasmic half of the presynaptic membrane at the active zone shows on its fracture face protruding particles whose Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved. counterparts are seen as pits on the fracture face of the outer membrane leaflet. Vesicles
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FIGURE 12-4: High-magnification (×145,000) view of freezesubstituted neuromuscular junctions in a muscle frozen during the abnormally large burst of acetylcholine release that is provoked by a single nerve stimulus in the presence of 2 mmol/l 4-aminopyridine. The stimulus was delivered 5.1 ms before the muscle was frozen. The section was cut unusually thin (~200Å) to show the fine structure of the presynaptic membrane, which displayed examples of synaptic vesicles apparently caught in the act of exocytosis. In all cases, these open vesicles were found just above the mouths of the postsynaptic folds, hence at the site of the presynaptic active zones. (With permission, Heuser, 1976.)
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
This case; Parkinson´s disease- main symptoms Tremor (at rest)
Hypokinesia Rigidity
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FIGURE 14-1: Biosynthetic pathway for catecholamines.
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
FIGURE 14-2: Schematic diagram of the phosphorylation sites on each of the four 60 kDa subunits of tyrosine hydroxylase (TOHase). Serine residues at the N-terminus of each of the four subunits of TOHase can be phosphorylated by a number of protein kinases. For the kinases underlined, there is reasonable evidence that they phosphorylate the enzyme in situ (Dunkley et al., 2004). Serine-40 can be phosphorylated by protein kinase A (PKA) and protein kinase G (PKG), MAPK-activated protein kinase 2 (MAPKAP2), calcium/calmodulin-dependent protein kinase II (CaM KII), and protein kinase C (PKC). Phosphorylation of serine-40 by PKA results in enzyme activation. Serine-31 can be phosphorylated by MAPK and cyclindependent kinase 5 (Cdk5). Phosphorylation of serine-31 leads to an increase in enzyme activity. Serine-19 is phosphorylated by CaM kinase II and MAPKAP2. Phosphorylation by CaM kinase II will activate the protein but only upon addition of the 14-3-3 protein. There is no evidence that phosphorylation of the serine-8 residue leads to tyrosine hydroxylase activation. Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
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FIGURE 14-3: Schematic of the D2 receptor and dopamine transporter. There is evidence that the D2S autoreceptor and the dopamine transporter bind to each other through the i3 of the D2S receptor and the amino terminal of the dopamine transporter (Lee et al., 2007).
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
FIGURE 14-5: Some catecholaminergic neuronal pathways in the rat brain. Upper. Some dopaminergic neuronal pathways. A9, substantia nigra cell group; A10, ventral tegmental cell group. Lower: noradrenergic neuronal pathways. A6, locus coeruleus; AC, nucleus accumbens; ACC, anterior cingulated cortex; CC, corpus callosum; FC, frontal cortex; HC, hippocampus; HY, hypothalamus; LC, locus coeruleus; ME, median eminence; MFB, median forebrain bundle; OT, olfactory tubercle; SM, striamedullaris; SN, substantia nigra; ST, striatum. (Courtesy of J.T. Coyle and S.H. Snyder).
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
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FIGURE 14-6: Effect of dopamine on intracellular signaling pathways. Stimulation of receptors by agonists can change enzyme activities as well as gene expression. The D1 family of receptors (D1 and D5) are coupled to adenylyl cyclase (AC) via a stimulatory GTP-binding protein (Gs) which consists of G , a and a subunit. The D2 family of receptors (D2, D3 and D4) inhibit adenylyl cyclase activity via coupling to an inhibitory GTP-binding protein (Gi). Activation of adenylyl cyclase leads to formation of cyclic AMP (cAMP) and activation of protein kinase A (PKA). The activated PKA phosphorylates, among other substrates, DARPP-32, which, when phosphorylated, will inhibit protein phosphatase-1. Activation of D1-family receptors will result in activation of mitogen-activated protein kinase (MAPK). A prominent substrate of PKA that alters gene transcription is CREB (cAMP-response element binding protein). In addition to inhibition of AC by G , activation of the D2 family of dopamine receptors results in dissociation of the subunit, which affects numerous activities. When dissociated from the G subunit, the subunit inhibits voltage-sensitive Ca2+ channels and activates voltage-sensitive K+ channels. The subunit will also activate a phospholipase C isozyme, leading to an increase in intracellular Ca2+. The Ca2+ leads to activation of kinases and phosphatases including MAPK, protein kinase C (PKC) and calmodulin (CaM)-stimulated enzymes such as Ca2+/calmodulin–stimulated protein kinases (CaMK), as well as protein phosphatase-2B (PP-2B, calcineurin). One substrate of PP-2B is DARPP-32. Through a mechanism involving -arrestin but independent of cAMP, activation of the D2 family of receptors inhibits Akt activity, leading to an activation of glycogen synthase-kinase 3 (GSK-3) activity, which has direct effects on gene transcription (Beaulieu et al., 2007). Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
TABLE 14-3: Properties of Human Dopamine Receptor Subtypes
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
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Other neurotransmitter systems than dopamine:
FIGURE 13-2: Transport, synthesis and degradative processes in a cholinergic presynaptic nerve terminal and synapse. The choline transport protein (ChT) functions at the nerve ending membrane to transport choline into the cytoplasm, where its acetylation by acetyl CoA is catalyzed by choline acetyltransferase (ChAT) to generate acetylcholine (ACh) in the vicinity of the synaptic vesicle. The vesicular acetylcholine transporter (VAChT) concentrates acetylcholine in the vesicle. ChT is also found on the vesicle but in a functionally inactive state. Upon nerve stimulation, depolarization and Ca2+ entry, AChcontaining vesicles fuse with the membrane and release their contents. The fusion of the membrane results in more ChT being exposed to the synaptic gap, where it becomes active. ACh is hydrolyzed to acetate and choline catalyzed by acetylcholinesterase (AChE), allowing for recapture of much of the choline by ChT. Because of the differing ionic compositions in the extracellular milieu and within the cell, ChT is thought to be active only when situated on the nerve cell membrane. Similarly, the VAChT may only be active when encapsulated in the synaptic vesicle (Ferguson & Blakely, 2004).
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
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FIGURE 13-3: Major cholinergic pathways in the rat brain. The principal source of cholinergic input to the cerebral cortex and hippocampus is the basal forebrain complex (BFC). Cell bodies in the nucleus basalis of Meynert project to the neocortex whereas cell bodies in the horizontal nucleus of the diagonal band and the magnocellular preoptic area project to the olfactory bulb, amygdala and limbic cortex. Cholinergic cell bodies located in the medial septal nucleus and vertical limb of the diagonal band project to the hippocampus and limbic cortex. The pedunculopontine and laterodorsal tegmental areas (PPT and LDT, respectively) preferentially innervate the brain stem and midbrain targets. Cholinergic interneurons predominate in the striatum. VTA, ventral tegmental area, IPN, interpeduncular nucleus. (Adapted with permission from the American College of Neuropsychopharmacology (ACNP), from Neuropsychopharmaclogy: The Fifth Generation of Progress, Picciotto et al., 2002).
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
FIGURE 13-8: Animals that have facilitated nAChR research. Upper panel: The marine ray Torpedo marmorata; a rich source of muscle-type nAChR present in its electric tissues that has allowed detailed structural determinations using electron microscopy. On the right is a ribbon diagram of Torpedo nAChR, viewed parallel with the membrane plane. For clarity, only the front two subunits are highlighted: in red, and in blue. Also shown is the location of trp149 (gold) at the agonistbinding site. The membrane is indicated by horizontal bars; E, extracellular; I, intracellular. From Unwin, 2005. Middle panel: the banded krait Bungarus multicinctus is a source of the potent nAChR antagonist -bungarotoxin, a component of this snake’s venom. The ‘threefinger’ structure of this polypeptide toxin is shown. Lower panel: The freshwater snail Lymnaea stagnalis yielded the novel AChBP. The crystal structure of this soluble protein provided a detailed molecular description of the agonist-binding site and confirmation of models based on other methods. On the right is a ribbon structure of the AChBP viewed from above. Each of the identical subunits is colored differently for clarity. One AChbinding region at the subunit interface is indicated. From Brejc, et al., 2001.
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
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FIGURE 13-11: Heterogeneity of nAChR family of subunits. Phylogenetic relationship of vertebrate nAChR subunits, adapted from Le Novère & Changeux (1995). The subunit composition of native nAChRs is illustrated on the right. Putative agonist-binding sites are indicated by dark circles between principal and complimentary adjacent subunits.
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
FIGURE 13-9: Structural features of the nAChR. Top left: Schematic representation of the sequence of various cys-loop receptor subunits including the AChBP, highlighting key conserved features. Reading from the N terminus, the disulfide-bonded cys loop is common to all these subunits and defines the family. The pair of vicinial cysteines close to the first transmembrane domain is a characteristic of nAChR subunits and the AChBP only. The colored boxes represent the four transmembrane segments, M1, M2, M3 and M4. The intracellular loop between M3 and M4 is variable in length. Top right: Orientation of a nAChR subunit within the membrane. Bottom: schematic of an assembled nAChR, with five subunits arranged to create a central ion channel, lined by M2. The N-terminal ACh-binding site is shown in the insert to be composed of three protein loops from the subunit (principal face) and three loops from the adjacent (complementary) subunit, in this case the subunit of a muscle nAChR. Key amino acid residues involved in ACh binding are indicated. Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
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FIGURE 13-13: Muscarinic cholinergic receptors can be subdivided based upon their G-protein–coupling characteristics and effector mechanisms. M1, M3 and M5 mAChRs preferentially couple to G-proteins of the Gq/G11 family, whereas M2 and M4 receptors typically activate G-proteins of the Gi/Go family. Agonist occupancy of the two groups of mAChRs results in the activation of different downstream effector proteins, as indicated, although some effectors (e.g., mitogen-activated protein kinase) (MAPK) are activated by both groups of receptors. Note that the effects of mAChR activation are mediated by both the and subunits of the G-proteins (see Chap. 21). An increase or decrease in the activity of the effector mechanism is indicated by the direction of the arrow. GIRK, G-protein–activated inwardly rectifying K+ channel; PLC , phosphoinositide-specific phospholipase C. (Figure adapted from Wess et al., 2007).
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
BOX FIGURE 13-1: Emergency workers in the Tokyo attack.
Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
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Glutamate as a aneurotransmitter
FIGURE 11-6: Excitatory and inhibitory neurotransmission have essential interactions with astrocytic metabolism. These processes are illustrated in the simplified schematic representation of key metabolic processes and release and uptake of neurotransmitters in glutamatergic and GABAergic synapses interacting with a surrounding astrocyte. The glutamate–glutamine cycle, including the glutamine synthetase (GS) reaction, is indicated in the glutamatergic neuron–astrocyte interaction. Analogously, the GABA–glutamate–glutamine cycle, including the GABA transaminase (GABA-T), succinate semialdehyde dehydrogenase (SSADH) and glutamate decarboxylase (GAD) reactions, is indicated in the GABAergic neuron–astrocyte interaction. The close association of the neurotransmitters, GABA and glutamate, to TCA cycle metabolism is indicated in all three cells. Glutamate is converted to -ketoglutarate via either glutamate dehydrogenase (GDH) or aspartate aminotransferase (AAT). GLN, glutamine; GLU, glutamate; -KG, -ketoglutarate; PAG, phosphate-activated glutaminase; TCA, tricarboxylic acid. Copyright © 2012, American Society for Neurochemistry. Published by Elsevier Inc. All rights reserved.
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The following powerpoints on clinical Parkinsons disease (PD) are a courtesy by Prof S Aquilonius and Prof H Askmark Uppsala university
Parkinsons sjukdom Degeneration av nigroneostriatala bansystem med dopaminbrist i neostriatum som följd
Cellförlust och förekomst av Lewy bodies i överlevande neuron i substantia nigra
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Parkinsons sjukdom- förekomst
15 per 100 000 (vanligare hos äldre, nära 1 % i pensionärsgruppen)
Medeldebutålder 55 - 60 år
Män och kvinnor drabbas lika ofta
Genetics Most cases appear as ”sporadic”, but first degree relatives have an increased risk
Genetic causes important in those with onset before age 50
Familial PD 12 forms assigned to different chromosome loci ex. PARK 1- alpha-synuclein mutation PARK 2- parkin mutation PARK 8- LRKK2 mutation
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Genetic predisposition
Enviromental factors and/or endogenous neurotoxins
Neurodegenerative process
Apoptosis
Pathogenic mechanisms Failure of the ubiquitin proteosomal system to clear cytotoxic material
Excitotoxicity
protein misfolding
Mitochondrial failure (complex 1)
Oxidative stress
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Psykiatriska symtom
Motoriska symtom: Tremor Akinesi Rigiditet Störd jämviktskontroll svarar på dopaminerg medicinering
Dysautonomi
BHB DOPAMIN L-DOPA AUTORECEPTOR
MAO
COMT DOPAMIN
DOPAMINAGONISTER
D1
D2
D1
D2
D1
DOPAMINRECEPTORER
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KOMPLIKATIONSFAS
TIDIG FAS SYMTOM FÖRBÄTTRING
DYSKINESIER SYMTOMFLUKTUATIONER PSYKISKA SYMTOM
TREMOR RIGIDITET HYPOKINESI
SYMTOMUTVECKLING MED L-DOPA BEHANDLING
3
5
ÅR
SYMTOMUTVECKLING UTAN TERAPI
Hur uppkommer motoriska fluktuationer? ”The storage hypothesis” Reducerat antal nervterminaler
Otillräcklig lagringskapacitet för dopamin bildat från tillfört L-DOPA
”Pulsatile stimulation” av dopaminreceptorerna Postsynaptiska förändringar
L-DOPA Motoriska fluktuationer Accentuerad neuronal skada?
Man eftersträvar i stället ”continuous dopaminergic stimulation”
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L-DOPA Fördelar:
Nackdelar:
mest potenta symtomlindrande läkemedlet
hög frekvens symtomfluktuationer efter några års behandling
förlänger överlevnaden
toxiska metaboliter neurotoxiskt in vivo?
DOPAMINAGONISTER Fördelar: ej beroende av fungerande dopaminerga neuron lägre frekvens motoriska fluktuationer inga toxiska metaboliter
Nackdelar: mindre potenta än L-DOPA biverkningsprofilen / tolereras ofta sämre än L-DOPA
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TERAPIÖVERSIKT MEDIKAMENTELL BEHANDLING
AMANTADIN ANTIKOLINERGIKA COMT-HÄMMARE DOPAMINAGONISTER L-DOPA SELEGILIN
OPERATION
PALLIDOTOMI “DEEP BRAIN STIMULATION” (TRANSPLANTATION)
STEREOTAXISK
FYSIOTERAPI
(TALAMOTOMI)
DIET ECT
Den nya läkemedelspaletten 1990
1970
1960 L-DOPA 1950 antikolinergika
2000
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THANKS FOR LISTENING
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