Neuropharmacology PHAR3202 Lecture Notes PDF

Neuropharmacology PHAR3202 A brief introduction to neurochemical transmission & neuromodulation Dr Natasha Kumar [email protected]  Objectives The lecture will explore: Cellular and molecular sites of drug action in CN...

Neuropharmacology PHAR3202 A brief introduction to neurochemical transmission & neuromodulation Dr Natasha Kumar [email protected]  Objectives The lecture will explore: Cellular and molecular sites of drug action in CNS The diversity of transmitters, and implications for drug action The process of neurotransmission Challenges of drug development for CNS diseases  Sites of drug action in the central nervous system (CNS) Examples of CNS Acting Drugs: Receptors - Dopamine agonists – Parkinson’s Disease - Dopamine antagonists – Schizophrenia Ion channels - Sodium channel blockers – epilepsy Enzymes - Acetylcholinesterase Inhibitor – Alzheimer’s Disease Transporter - Selective serotonin reuptake inhibitor – depression / anxiety Figure 3.1 - Rang and Dale’s Pharmacology, 9th Edition  Types of receptors in CNS Figure 3.2- Rang and Dale’s Pharmacology, 9th Edition  Neuropharmacology – general principles Drugs can act via regulating transmitter release, reuptake, metabolism or can act directly on neurotransmitter receptors Many commonly used CNS drugs can interfere with neurotransmission In many cases, the precise mechanism of action of many therapeutically useful CNS drugs is unknown Each stage of neurotransmission is a potential site of drug action 1. Action potential in presynaptic nerve 2. Synthesis of transmitter (increase, decrease or enhance) 3. Storage 4. Metabolism 5. Release 6. Reuptake (nerve or glia) 7. Degradation 8. Receptor binding (activation, enhance or inhibit activation) 9. Receptor-induced increase or decrease in ionic conductance 10. Retrograde signalling Chemical transmission occurs at CNS synapses Criteria for transmitter: Transmitter made/stored in vesicles Transmitter released upon nerve stimulation Action is terminated in some way Exogenous application mimics effects of nerve stimulation  CNS Neurotransmitters - a diverse range of chemicals Biogenic Amines - serotonin, dopamine, noradrenaline & adrenaline - acetylcholine Serotonin Dopamine Amino acids - GABA, glutamate GABA Peptides Acetylcholine - opioids (endorphin), tachykinins (substance P), Adrenaline Noradrenaline neuropeptide Y (NPY) Glutamate Purines - ATP, adenosine ATP Diffusible mediators Endorphins Substance P Nitric Oxide - nitric oxide, carbon monoxide An example of the complexity of a neuronal terminal  Chemical transmission in the CNS Critical features – release of transmitter Activation of receptor (s) Breakdown (enzyme) or removal of transmitter from the synapse – may involve specific transporters Note – there is much redundancy in transmitter functions – many neurotransmitters may serve similar function…….. Anatomic specificity – particular circuits have specific neurotransmitters GLUTAMATE  Some key markers of neurotransmission TRANSMITTER PROTEIN MARKERS Amino acids γ-Aminobutyric acid (GABA) Glutamic acid decarboxylase Glutamate Enzymes operating general metabolism Monoamines Dopamine Tyrosine hydroxylase Noradrenaline Tyrosine hydroxylase & dopamine β-hydroxylase Adrenaline Tyrosine hydroxylase, dopamine β-hydroxylase, PNMT Serotonin Tryptophan hydroxylase Acetylcholine Choline acetyltransferase Nitric Oxide Neuronal nitric oxide synthase Neuropeptides Respective peptide Choline acetyltransferase galanin AMPA Receptor Tyrosine hydroxylase Brain cell types  Neuropharmacology – drug classification 1. Classify according to transmitter system that the drug acts upon (e.g. Dopamine or Acetylcholine etc...) 2. Drugs acting in the CNS are also classified according to application or indication (e.g. Antidepressant drugs are used to treat depression, antipsychotics are used to treat schizophrenia, anxiolytics are used to treat anxiety etc...)  Centrally acting drugs….…. Can produce dependence with prolonged use Used for social purposes as well as a range of therapeutic uses In order to exert an effect, the drug must access the brain (needs to cross the BBB) Major implications for drug development  Summary Neurochemical transmission Molecular and cellular targets of transmitters Transmitter localisation and function Receptor localisation and function Drug treatment strategies for CNS conditions Neuronal survival / death Implications for drug development see you at the Q&A   Exam-style revision question A) What are the THREE major mechanisms for termination of neurotransmitter action (3 marks), and how do they differ in their efficiency and speed (3 marks)? B) Provide ONE example of a neurotransmitter that is terminated by each mechanism (3 marks). To be discussed during the Q&A  Neuropharmacology PHAR3202: Acetylcholine / Dopamine Nicole Jones Department of Pharmacology [email protected] References: Nestler, Hyman, Holtzman & Malenka: Molecular Pharmacology : A foundation or clinical Neuroscience 3nd Edition (chapter 6) Rang, Dale Ritter & Flower: Pharmacology 7th edition (chapter 13, 38) Katzung: Basic & clinical pharmacology 15th ed (chapter 21)  Learning Objectives At the end of this lecture you should be able to: Describe the synthetic / metabolic pathways for acetylcholine and dopamine Discuss some of the functions mediated by these neurotransmitters Discuss the different classes of drugs affecting cholinergic and dopaminergic neurotransmission (and how these drugs affect function) Acetylcholine (ACh) synthesis and metabolism Choline + Acetyl coenzyme A Choline acetyl transferase (ChAT) Acetylcholine + Coenzyme A Acetylcholinesterase (AChE) Choline + Acetate Adapted from Nestler, Hyman, Malenka 2008 – McGraw-Hill  Acetylcholinesterase (AChE) Untreated neuron Acetylcholinesterase (AChE) hydrolyses ACh into choline and acetate AchE is located in cytoplasm and outer cell membrane and can metabolise intra/extracellular ACh Blocking AChE – leads to accumulation of released ACh Question: why would an accumulation of ACh be helpful / or harmful? Come to the Q&A to discuss this question further  Cholinergic pathways Abbreviations Am – Amygdala Hip – Hippocampus Hyp – Hypothalamus C – Cerebellum Str – Corpus striatum Th – Thalamus Sep – Septum SN – Substantial nigra  CNS roles for ACh Memory Attention Movement Arecoline – cholinergic agonist Addiction Hyoscine – muscarinic antagonist Mood Alzheimer’s disease patients – loss of memory related to degeneration of cholinergic neurons Scopolamine (muscarinic antagonist) – induces memory deficits, reversed using donepezil (Acetylcholinesterase inhibitor)  Cholinergic Receptors Nicotinic Receptors Muscarinic Receptors Ligand-gated ion Channels (LGICs) G protein-coupled receptors (GPCRs) Nicotinic receptors are pentameric (5) proteins. Made up of combinations of α,β,γ,δ and ε subunits Muscle-types (N1 or NM) are formed with α,β,γ,δ,ε Neuronal-types (N1 orNN) are formed with α or α & β subunits. ε α1 α1 δ β1 Muscle α7 β2 α7 α7 α4 α4 α7 α7 β2 β2 Neuronal Neuronal Santiago and Abrol Int. J. Mol. Sci. 2019, 20, 5290 Kandel ER, Schwartz JH: Principles of Neural Science, 4th ed. New York, Elsevier, 2000  Muscarinic ACh receptors G-protein coupled receptors 5 subtypes – ALL expressed in brain Receptor Brain Localization M1 Cortex, Hippocampus, striatum M2 Basal forebrain, thalamus M3 Cortex, hippocampus, thalamus M4 Cortex, striatum, hippocampus Moran et al., (2019) TiPS 40(12):1006-1020 M5 Substantia nigra * Not many selective drugs at all – and hardly any used clinically (as yet) for CNS disorders!! Adapted from Nestler, Hyman, Malenka 2008 – McGraw-Hill  Nicotinic ACh receptors Nicotinic acetylcholine receptor subtypes are broadly distributed in the brain Nature Reviews Drug Discovery 8, 733-750 (September 2009) | doi:10.1038/nrd2927 Nicotinic receptors: allosteric transitions and therapeutic targets in the nervous system Antoine Taly1, Pierre-Jean Corringer2, Denis Guedin3, Pierre Lestage3 & Jean-Pierre Changeux4  Sites of action of drugs that modulate the function of Acetylcholine Storage Release Synthesis Receptor Metabolism Receptor Nestler, Hyman, Malenka 2008 – McGraw-Hill  Drugs Targeting Muscarinic ACh Receptors Agonists – none used to clinically to treat CNS conditions – a lack of selectivity across the 5 subtypes leads to side effects Positive allosteric modulators show better sub-type selectivity. Clinical trials for Alzheimer's Disease (M1- selective), Schizophrenia (M1/M4 selective) are currently being conducted  Antagonists –scopolamine, benzotropine Benzotropine – adjunct to Parkinson’s Disease therapy Scopolamine – motion sickness Negative allosteric modulators selective for M5, being investigated in pre-clinical models of Parkinson’s disease Some tricyclic antidepressants and antipsychotic drugs (chlorpromazine) have muscarinic antagonist activity – which contributes to their side effect profile. Question: What are the peripheral and CNS side effects we would predict from off-target muscarinic receptor inhibition? Come to the Q&A to discuss this question further  CNS effects of nicotine Nicotine is a nAChR agonist Generally delivered via smoking tobacco or transdermal patches, gum. Crosses the blood brain barrier easily Involved in pleasure, reward and addiction Stimulates release of dopamine in nucleus accumbens (pleasure centre in brain) Regular nicotine exposure – changes in receptor numbers and sensitivity of receptors (desensitisation) Reinforcing properties of nicotine Self-administration of nicotine – blocked with β2 nAChR subunit blocker Mice with β2 nAChR subunit knockout – do not self-administer nicotine – but do administer cocaine Laviolette & van der Kooy, 2004 Nature Rev Neuroscience 5 : 55-65  Nicotine – it’s not all bad....?? Nicotine Smoking reduces incidence of Parkinson’s Disease Direct neuroprotective actions in cultured neurons Can reduce some behavioural symptoms in Tourette’s syndrome patients Replacement therapy for smoking cessation (patches, gum)  Drugs Targeting nAChRs VERY FEW neuronal nAChR drugs used clinically for CNS disorders!! Curare – blocks muscle and neuronal nAChRs – paralysis Succinylcholine – paralysis during anaesthesia Hexamethonium, mecamylamine – block nAChRs in sympathetic/parasympathetic ganglia in autonomic nervous system Varenicline – partial agonist at nAChRs a treatment for smoking sensation. High affinity for the α4 β2 nAChR. http://news.bbc.co.uk/2/hi/health/7115696.stm 1. Nicotine from a cigarette stimulates the release of dopamine from nucleus accumbens 2. When a smoker quits, the lack of nicotine leads to reduced levels of dopamine, causing feelings of craving and withdrawal 3. As a partial agonist varenicline both blocks nicotine binding to nACh receptors and activates moderate dopamine release to alleviate withdrawal symptoms  Drugs inhibiting AChE Therapeutic advantage – when there is a deficit in cholinergic signalling Centrally acting AChE inhibitors – donepezil, galantamine and rivastigmine –delay cognitive deficits in Alzheimer’s patients indicated for the treatment of AD from the mild stages onwards Parsons et al., Neurotox Res (2013) 24:358–369 AChE inhibitors aim to boost ACh levels and alleviate disease symptoms associated with the progressive loss of cholinergic function in Alzheimer's disease  Common therapeutic drugs that affect ACh system in CNS? Alzheimer’s Disease (AD): AChE inhibitors – e.g. Donepezil, rivastigmine and galantamine – AChE Inhibitors – effective in slowing down cognitive deficits in AD patients Parkinson’s Disease (PD): Muscarinic antagonist e.g. benzotropine – adjunct to PD therapy Smoking cessation: nicotinic agonists - nicotine (patches, gum), partial agonist (e.g Varenicline)  Dopamine (DA) Nobel prize for medicine 2000 (2/3 – related to dopamine) “for their discoveries concerning signal transduction in the nervous system“ Arvid Carlsson (Sweden) – work 50 years ago Dopamine is a transmitter in the brain Important for movement Dopamine antagonists – effective in schizophrenia Paul Greengard (USA) Slow signalling by DA receptors (2nd messengers) Regulatory protein DARPP-32 Dopamine synthesis Tyrosine Tyrosine hydroxylase Dihydroxyphenylalanine (Dopa) L-Aromatic amino acid decarboxylase Dopamine Dopamine metabolism  Dopaminergic pathways Mesolimbic/Mesocortical pathways – ventral tegmental area – project to limbic (amygdala, nucleus accumbens) and cortical (frontal) structures Nigrostriatal pathway – substantia nigra – project to striatum Tuberoinfundibular (or tuberohypophyseal) pathway – arcuate nucleus (hypothalamus) – projections to pituitary Others in retina, olfactory system Abbreviations Am – Amygdala Hip – Hippocampus Ac – Nucleus Hyp – Hypothalamus accumbens C – Cerebellum P – Pituitary Str – Corpus striatum Th – Thalamus Sep – Septum SN – Substantial nigra  Dopaminergic roles Movement Memory Mood Reward Addiction Vomiting  Dopamine and Movement Ablation of substantia nigra in rats – causes catalepsy Lesions using 6-hydroxydopamine – causes selective death of catecholaminergic neurones Circling behaviour toward lesion when animals exposed to amphetamine – imbalance of dopamine Nestler, Hyman, Malenka 2001 – McGraw-Hill D2 knockout mice reduces spontaneous motor activity  Dopamine and Movement Involving mesolimbic and mesocortical systems Amphetamine – reduces “normal” behaviours, and causes “stereotypical” behaviours Reduced by DA antagonists, not by drugs blocking NA, also prevented in animals with lesions of DA neurones (6-OH-dopamine) Stereotypy relates to hyperactive nigrostriatal pathway Parkinson’s disease – degeneration of dopaminergic neurones in nigrostriatal pathway – dopamine deficiency Decreased motor control Antipsychotic drugs – D2 antagonists Motor dysfunction is major side effect Blocking D2 receptors in nigrostriatal pathway  Dopamine and Reward Reward = making things better Consumption of reward (nice food, wine, sex, addictive drug) – causes pleasure Learning process, using cues to predict Nucleus accumbens is pleasure centre of brain Cocaine and amphetamine activate this reward pathway D1 receptor mediated – D1 knockout mice unmotivated – don’t want to eat, insensitive to amphetamine, cocaine Dopamine and Reward Wise, Nature Neuroscience Reviews (2004) 5: 1-12  Sites of action of drugs that modulate the function of dopamine Storage Synthesis Metabolism Release / Re-uptake Receptor Receptor Metabolism Nestler, Hyman, Malenka 2008– McGraw-Hill  Dopamine Receptors All are G-protein coupled receptors D1 family (D1, D5) – Gs coupled – increase AC D2 family (D2, D3, D4) – Gi coupled – decrease AC Receptor Agonist Antagonist Brain Localization Neostriatum, cortex, D1 SKF82958 haloperidol nucleus accumbens, olfactory tubercle Raclopride, Neostriatum, nucleus Bromocriptin D2 sulpiride, accumbens, olfactory e haloperidol tubercle Quinporole. D3 raclopride Nucleus accumbens 7-OH-DPAT D4 Clozapine Midbrain, amygdala Hippocampus, D5 SKF38393 SCH23390 hypothalamus Adapted from Nestler, Hyman, Malenka 2008 – McGraw-Hill  Dopamine Receptor Drug Classes Agonists – dopamine, apomorphine Antagonists – chlorpromazine, haloperidol, spiperone, sulpiride, clozapine, aripiprazole Mainly used as antipsychotic medications Affecting dopamine reuptake – inhibition (cocaine), substrate / release (amphetamine) - indirectly Question: Can you think of some of the potential side effects of drugs affecting dopamine neurotransmission (too much / not enough) given its roles in normal brain function? Come to the Q&A to discuss this question further  Common therapeutic drugs that affect DA system in CNS? Parkinson’s Disease (PD): dopamine precursor (L-dopa), prevent metabolism in periphery and brain (DDC, MAO, COMT inhibitors), dopamine agonists Antipsychotics: dopamine antagonists  Learning Objectives At the end of this lecture you should be able to: Describe the synthetic / metabolic pathways for acetylcholine and dopamine Discuss some of the functions mediated by these neurotransmitters Discuss the different classes of drugs affecting cholinergic and dopaminergic neurotransmission (and how these drugs affect function)  Revision Questions 1. Discuss the following stages of acetylcholine / dopamine neurotransmission: location and mechanism of synthesis, location and mechanism of metabolism and sites of action. 2. Discuss TWO therapeutic drug classes acting at different targets of the cholinergic / dopaminergic system in CNS. In you answer include the condition being treated, the receptor/enzyme being targeted, the action of the drug at the target. 3. Identify some of the side effects (CNS and peripheral) that might occur when acetylcholine / dopamine levels are too high (or too low) – or if the systems are over / under stimulated Come along to the Q&A to discuss further Neuropharmacology PHAR3202: Serotonin / Noradrenaline Nicole Jones Department of Pharmacology [email protected] References: Nestler, Hyman, Holtzman & Malenka: Molecular Pharmacology : A foundation or clinical Neuroscience 3nd Edition (chapter 6) Rang, Dale Ritter & Flower: Pharmacology 7th edition (chapter 14, 38) Katzung: Basic & clinical pharmacology 15th ed (chapter 21)  Learning Objectives At the end of this lecture you should be able to: Describe the synthetic / metabolic pathways for serotonin / noradrenaline Discuss some of the functions mediated by serotonin / noradrenaline Discuss the different classes of drugs affecting serotonin/ noradrenaline neurotransmission and how these drug classes affect function Serotonin / 5 hydroxytryptamine (5HT) Synthesis Tryptophan Tryptophan hydroxylase 5-hydroxytryptophan L-Aromatic amino acid decarboxylase 5-hydroxytryptamine (5HT) Serotonin / 5 hydroxytryptamine (5HT) Metabolism 5-hydroxytryptamine (5HT) Monoamine oxidase 5-hydroxyindole acetaldehyde Aldehyde dehydrogenase 5-hydroxyindole acetic acid (5-HIAA) Note: 5HT is also metabolised in the liver by this pathway  Serotonergic pathways in the CNS Abbreviations Am – Amygdala Hip – Hippocampus Hyp – Hypothalamus C – Cerebellum Str – Corpus striatum Th – Thalamus Sep – Septum SN – Substantial nigra  CNS roles for Serotonin / 5HT Hallucinations Behaviour Sleep Mood, emotion Memory Autonomic control Migraine  5HT and Hallucinations LSD (Lysergic acid diethylamide) – 5HT analogue (5HT2 agonist) Decrease in firing of 5HT brainstem neurones “Psychadelic” drug – popular in 60’s, 70’s Cause hallucinations (audio, visual) and disturbed thought processes Other hallucinogens – DMT, psilocybin, mescaline – also act via 5HT2 Simply increasing 5HT levels does not necessarily result in hallucinations (because 5HT also acts at other 5HT receptor subtypes)  5HT and Sleep Lesion of raphe nucleus (deplete 5HT levels) – can reduce sleep Injection of 5HT into animals can induce sleep Preventing serotonin production reduces sleep in rodents and zebrafish Tryptophan hydroxylase (tph) knockout zebrafish are more active and sleep less Oikonomou et al., (2019) Neuron 103(4):686-701. However – in humans 5HT precursors (tryptophan, 5-hydroxytryptophan) – do not induce sleep in people with insomnia  5HT and Memory 5HT receptor localization in brain areas involved in memory (hippocampus, amygdala, cortex) Alzheimer’s and schizophrenic patients – decreased 5HT levels correlate with cognitive impairments Many 5HT drugs can improve memory Genetic variation 5HT2a humans – decreased performance in memory task  5HT receptors 14 receptor subtypes. All GPCRs, except 5HT3 which is a ligand-gated ion channel (LGIC) A lot of drugs affecting 5HT receptors, most do not have good selective, BUT there are many used clinically Receptor Gα Signalling response 5HT3 LGIC (iontropic) GPCR (metabotropic) Subtype 5HT1A/1B/1D/1E/1F Gi Decreases cAMP levels 5HT2A/2B/2C Gq Increase intracellular calcium 5HT4 Gs Increase cAMP levels 5HT5 ? 5HT6 Gs Increase cAMP levels 5HT7 Gs Increase cAMP levels Question: Why is subtype selectivity an important quality for a therapeutic drug to have? Come to the Q&A to discuss this question further “Fundamental Neuroscience” Zigmond, Bloom, Landis, Roberts, Squire; Academic Press, 1999 5HT pharmacology and localization Receptor Agonist Antagonist Brain Localization 5HT1A 8-OH-DPAT, buspirone, WAY 100135, Spiperone Hippocampus, septum, amygdala, dorsal raphe, cortex gepirone Methiothepin, Ergotamine 5HT1B 5-CT Methiothepin Substantia nigra, basal ganglia 5HT1D Sumatriptan GR 127935 Substantia nigra, striatum, hippocampus 5HT1E ?? 5HT1F Dorsal raphe, hippocampus, cortex 5HT2A DMT, LSD, psychadelics Ketanserin, cinanserin, Cortex, olfactory tubercle MDL900239 5HT2B DMT NOT IN BRAIN 5HT2C DMT, MCPP Mesulergine, fluoxetine Basal ganglia, choroid plexus, substantia nigra 5HT3 Ondansetron, granisetron Spinal cord, cortex, hippocampus, brain stem nuclei 5HT4 Metoclopramide; GR113808 Hippocampus, nucleus accumbens, striatum, substantia nigra 5HT5A Methiothepin Cortex, hippocampus, cerebelum 5HT5B Methiothepin Habenula, CA1 hippocampus 5HT6 Methiothepin, clozapine, Striatum, cortex, hippocampus amitriptyline 5HT7 Methiothepin, clozapine, Hypothalamus, thalamus, cortex, suprachiasmatic amitriptyline nucleus Adapted from Nestler, Hyman, Malenka 2008– McGraw-Hill  Sites of action of drugs that modulate the function of 5HT Synthesis Storage Receptor Re-uptake Metabolism Receptor Receptor Receptor Nestler, Hyman, Malenka 2008– McGraw-Hill  5HT transporter (SERT) Re-uptake of 5HT from synaptic cleft Similar structure to noradrenaline / dopamine transporters (NET/DAT) High levels of protein expression throughout brain (projections, nerve terminals) Drugs which inhibit/affect transport – can promote/prolong 5HT signalling SERT radioligand autoradiography in Baboon brain sections Szabo, et al Caron & Gether. Nature 532, 320–321 (2016). J Nucl Med. 2002;43:678-692.  Drugs affecting SERT MDMA (3,4-methylenedioxy methamphetamine - Ecstasy) Substrate for SERT, can release 5HT from nerve terminals, and agonist at 5HT2 MDMA (5 mg/kg daily) for 4 d at 2x intervals prior to imaging Mood elevation, altered perception Side effects: tachycardia, hyperthermia, panic, neurotoxicity? MDMA is taken up into the nerve terminal via SERT and enters the synaptic vesicles via VMAT. These transporters are usually uni-directional but MDMA Szabo, et al alters their function converting them into J Nucl Med. 2002;43:678-692. bidirectional/exchange transporters leading to the removal of serotonin from the vesicle and then release from the synapse and its accumulation in the synaptic cleft activating post synaptic receptors.  Other drugs acting at SERT Antidepressants – high affinity for SERT Selective serotonin reuptake inhibitors (SSRIs – e.g. fluoxetine, sertraline) tricyclic antidepressants (clomiprimine) Cocaine – inhibits SERT, NET and DAT – prevents reuptake 5HT, NA, DA, so levels of these neurotransmitters in the synapse remain high  Common therapeutic drugs that affect 5HT system in CNS? Migraine: e.g. Triptans, 5-HT1D agonist Anxiolytic: 5-HT1A partial agonist Antipsychotics: many of these have 5HT2A/2C antagonist activity Nausea and vomiting: 5-HT3 antagonists (e.g. ondansetron) used for chemotherapy induced nausea and vomiting. Also anxiolytic, memory enhancing actions observed Antidepressants: e.g. SSRIs - SERT inhibitor (more 5-HT in synapse). Used to treat depression, OCD, various anxiety disorders with relatively few side effects  Serotonin syndrome – when there is too much Excess synaptic level of 5HT due to high intake of serotonergic drugs, e.g., SSRI + another antidepressant can lead to serotonin syndrome Overstimulation of 5HT1A and 5HT2 receptors. Symptoms develops within hours. CNS effects: insomnia, confusion, hallucination, coma, tremor, rigidity, hyperreflexia. Autonomic effects: ↑ or ↓ BP, ↑ HR, diarrhea, fever. Noradrenaline (NA) Synthesis Tyrosine Tyrosine hydroxylase Dihydroxyphenylalanine (Dopa) L-Aromatic amino acid decarboxylase Dopamine Dopamine β hydroxylase Noradrenaline Phenylethanolamine – N- methyltransferase (PNMT) Adrenaline  Noradrenaline Metabolism Metabolism in Nerve Terminals Noradrenaline Adrenaline Monoamine oxidase (MAO) 3,4 Dihydroxymandelic acid Catechol-o-methyltransferase (COMT) Vanillylmandelic acid Note: noradrenaline is metabolised in the liver first by COMT and then MAO Noradrenergic pathways in brain Select few brainstem nuclei Mainly locus coeruleus (LC) Terminals widespread (cortex, hippocampus) Used by sympathetic neurons of autonomic nervous system α, β adrenergic receptors Abbreviations Am – Amygdala LC – Locus coeruleus Hip – Hippocampus NTS - Nucleus tractus solitarius Hyp – Hypothalamus MFB – Medial forebrain bundle C – Cerebellum Str – Corpus striatum Th – Thalamus Sep – Septum SN – Substantial nigra CNS roles for NA Sleep Attention Arousal (fear, stress) Learning, memory Mood (depression, anxiety) Blood pressure regulation  NA and fear, stress LC neurons respond to stressful stimuli Yohimbine (α2 antagonist) – increase firing of LC neurones, induces fear/anxiety. Khoshbouei, H., et al., 2002. Pharmacol. Biochem. Behav. 71, 407– 417. NA - fear, stress & memory  NA and memory Increasing NA levels enhances memory β antagonist – Propranolol – reduces memory performance Emotional memory in humans involves central β adrenoreceptors (possible use in PTSD?) Van Stegeren 2008, Acta Psychologica 127; 532-541  NA and sleep/arousal Recordings from LC neurons in rats during the sleep-wake-cycle Silent while asleep Increased activity following arousal Aston-Jones, 2005 Sleep Medicine 6 (Suppl 1) S3-7 NA pharmacology and receptor localization Receptor Agonist Antagonist Localization α1 Phenylephrine Prazosin Cortex, Hippocampus, Methoxamine Indoramin Brainstem α2 Clonidine Yohimbine Cortex, Brainstem, Rauwolscine Midbrain, Spinal cord Prazosin β1 Isoproteronol Alprenolol Olfactory nucleus, cortex, Terbutaline Betaxolol cerebellum, brainstem, Propranolol spinal cord β2 Procaterol Propranolol Olfactory bulb, piriform Zinterol cortex, hippocampus, cerebellum β3 Pindolol Bupranolol Propranolol Adapted from Nestler, Hyman, Malenka 2008 – McGraw-Hill  Sites of action of drugs that modulate the function of noradrenaline Storage Synthesis Metabolism Re-uptake Receptor Receptor Metabolism Receptor Receptor Nestler, Hyman, Malenka 2008– McGraw-Hill  Uptake 1 / NA transporter (NET) Re-uptake of NA from synaptic cleft Similar structure to SERT, DAT (serotonin / dopamine transporters) High levels of protein expression throughout brain (projections, nerve terminals) Drugs which inhibit/affect transport – can promote/prolong NA signalling Shannon et al., (2000) N Engl J Med; 342:541-549  Uptake 1/Noradrenaline Transporter (NET) Inhibitors Mechanism of Action Block the uptake of noradrenaline into the nerve terminal, increasing the duration of action of the released noradrenaline Tricyclic antidepressants Cocaine (TCAs) Actions and Uses Increased NA in synapse Inhibits NET, SERT and DAT – and Used to treat depression prevent the reuptake of 5HT, NA, DA Used as local anaesthetic/drug of abuse Adverse Effects Postural hypotension (α1-AR antagonist), Hypertension, excitement, sedation (Histamine H1-R antagonist ), dry convulsions, dependence mouth, blurred vision, constipation (Muscarinic-R antagonist) Contraindications Monoamine oxidase inhibitors Question: Can you explain why MAO inhibitors are contraindicated when taking TCAs? Come to the Q&A to discuss this question further  Amphetamine actions Amphetamine Amphetamine is taken up into the nerve terminal via NET-1 and enter the synaptic vesicles via VMAT. Both these transporters are usually uni-directional but amphetamine alters their function converting them into bidirectional/exchange transporters leading to the removal of noradrenaline from the vesicle and then the synapse and its accumulation in the synaptic cleft activating post synaptic receptors. Indications CNS stimulant in narcolepsy, ADHD, appetite suppressant, VMAT=Vesicular monoamine transporter nasal decongestion (ephedrine) Uptake1 = Norepinephrine transporter (NET1) Rang, Dale, Ritter, Moore “Pharmacology” 7th edition,  Monoamine Oxidase Inhibitors: Moclobemide Mechanism of action: Decreased metabolism of noradrenaline. Blocks the enzyme that degrades noradrenaline – Monoamine oxidase (MAO) leading to increased noradrenaline levels Moclobemide Indication Depression Adverse Effects sleep disturbances, dizziness, nausea, headache, anxiety and “cheese effect” which is a hypertensive crisis when foods containing tyramine are eaten (liver, red wine, cheese & vegemite) Contraindications Other antidepressants, drugs affecting catecholamines  Common therapeutic drugs that affect NA in CNS? Depression: Antidepressants (TCAs, MAO Inhibitors, selective noradrenaline reuptake inhibitors) ADHD: Stimulants Methylphenidate (ADHD) Amphetamines (ADHD, narcolepsy) Parkinson’s Disease: NA synthesis inhibitors Carbidopa (Parkinson’s) Can you think of some adverse effects associated with modulating NA system (too much/too little)??  Learning Objectives At the end of this lecture you should be able to: Describe the synthetic / metabolic pathways for serotonin / noradrenaline Discuss some of the functions mediated by serotonin / noradrenaline Discuss the different classes of drugs affecting serotonin/ noradrenaline neurotransmission and how these drug classes affect function  Revision Questions 1. Discuss the following stages of serotonin / noradrenaline neurotransmission: location and mechanism of synthesis, location and mechanism of metabolism and sites of action. 2. Discuss TWO therapeutic drug classes acting at different targets of the serotoninergic/noradrenergic system in CNS. In you answer include the condition being treated, the receptor being targeted, the action of the drug at the target. 3. Identify some of the side effects (CNS and peripheral) that might occur when serotonin / noradrenaline levels are too high (or too low) – or if the systems are over / under stimulated Come along to the Q&A to discuss further