Neuropharmacology 3202 Serotonin / Noradrenaline
Nicole Jones Department of Pharmacology
UNSW [email protected]
References • Nestler, Hyman & Malenka: Molecular Pharmacology : A foundation for clinical Neuroscience 2nd Edition (chapter 6) • Rang, Dale Ritter & Flower: Pharmacology 7th edition (chapter 33) • Katzung: Basic & clinical pharmacology 7th ed (chapter 21) • Goodman and Gilman’s Pharmacology (chapter 12)
At the end of this lecture you should be able to: • Describe the synthetic / metabolic pathways
for serotonin and noradrenaline • Discuss some of the functions mediated by
these neurotransmitters • Discuss the different classes of drugs affecting
serotonin and noradrenaline neurotransmission (and how these drugs affect function), and provide named examples
Learning Objectives
Serotonin – 5 hydroxytryptamine (5HT)
Tryptophan
5-hydroxytryptophan
5-hydroxytryptamine (5HT)
5-hydroxyindoleacetic acid (5HIAA)
Tryptophan hydroxylase L-Aromatic amino acid decarboxylase Monoamine oxidase Aldehyde dehydrogenase
Serotonergic pathways
CNS roles for 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 • Hallucinations (audio, visual) • Disturbed thought processes • Other hallucinogens – DMT, psilocybin,
mescaline – also act via 5HT2
5HT and Sleep
• Lesion of raphe nucleus deplete 5HT – reduce sleep
• Injection of 5HT into animals can induce sleep
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
• Genetic variation 5HT2a humans – decreased performance in memory task
• Many 5HT drugs can improve memory
5HT receptors • Many receptor subtypes (14 so far). All except
5HT3 – GPCRs
• A lot of drugs affecting 5HT, not really selective, BUT there are many used clinically
“Fundamental Neuroscience” Zigmond, Bloom, Landis, Roberts, Squire; Academic Press, 1999
Ionotropic Metabotropic
5HT neuron
Nestler, Hyman, Malenka 2008– McGraw-Hill
Receptor Agonist Antagonist Brain Localization
5HT1A 8-OH-DPAT, buspirone, gepirone
WAY 100135, Spiperone Methiothepin, Ergotamine
Hippocampus, septum, amygdala, dorsal raphe, cortex
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, MDL900239
Cortex, olfactory tubercle
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, amitriptyline
Striatum, cortex, hippocampus
5HT7 Methiothepin, clozapine, amitriptyline
Hypothalamus, thalamus, cortex, suprachiasmatic nucleus
5HT pharmacology and localization
Adapted from 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
J Nucl Med. 2002;43:678-692. Szabo, et al
SERT radioligand Autoradiography in Baboon brain sections
Drugs affecting SERT • MDMA (3,4-methylenedioxy
methamphetamine - Ecstasy) • Substrate for SERT, can release 5HT from
nerve terminals, and agonist at 5HT2 • Mood elevation, altered perception • Side effects: tachycardia, hyperthermia, panic,
neurotoxicity?
J Nucl Med. 2002;43:678-692. Szabo, et al MDMA (5 mg/kg daily) for 4 d
at 2x intervals prior to imaging
• 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
Other drugs acting at SERT
Interference with the 5HT system
• Activate / block receptors __________________ • Inhibit synthesis: ________________________ • Inhibit neuronal re-uptake: _________________ • Depletion: __________________________ • Inhibit metabolism: ________________________ • Promote release: __________________________
Common therapeutic drugs that affect 5HT system in CNS?
• Sumatriptan: 5-HT1D agonist: migraine • Buspirone: 5-HT1A partial agonist: anxiety • Clozapine: 5HT2A/2C antagonist: antipsychotic • Ondansetron: 5-HT3 antagonist: chemotherapy
induced nausea and vomiting. Also has anxiolytic, memory enhancing actions.
• Fluoxetine: SERT blocker (more 5-HT in synapse). Used to treat depression, OCD, various anxiety disorders with relatively few side effects
Serotonin syndrome • Excess synaptic level of 5-HT due to high intake of
serotonergic drugs, e.g., fluoxetine + other antidepressant
• Overstimulation of 5-HT1A and 5-HT2 receptors. • Symptoms develops within hours. • Mental effects: insomnia, confusion, hallucination,
coma. • Autonomic effects: ↑ or ↓ BP, ↑ HR, diarrhea,
fever. • Neurological effects: tremor, rigidity, hyperreflexia.
5HT in one line
Noradrenaline Synthesis
Tyrosine hydroxylase L-Aromatic amino acid decarboxylase Dopamine β hydroxylase Phenylethanolamine – N-methyltransferase (PNMT)
Tyrosine
Dihydroxyphenylalanine (Dopa)
Dopamine
Noradrenaline
Adrenaline
Noradrenaline Metabolism
Noradrenaline Monoamine oxidase (MAO) Catechol-O-methyl transferase (COMT) •3-methoxy-4-hydroxy-
mandelic acid (VMA) •3-methoxy-4-hydroxy- phenylglycol (MHPG)
Noradrenaline Nestler, Hyman, Malenka 2008 – McGraw-Hill
Noradrenergic pathways in brain
NA-containing Neurons
• Select few brainstem nuclei • Mainly locus coereleus (LC) • Terminals widespread (cortex, hippocampus) • Used by sympathetic neurons of autonomic
nervous system • α, β adrenergic receptors
CNS roles for NA
• Sleep • Attention • Arousal (fear, stress) • Learning, memory • Mood (depression, anxiety) • Blood pressure regulation
NA and fear, stress • LC cells 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
• NA 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 neurones
– Silent while asleep – Increased activity following arousal
Aston-Jones, 2005 Sleep Medicine 6 (Suppl 1) S3-7
Receptor Agonist Antagonist Localization
α1 Phenylephrine Methoxamine
Prazosin Indoramin
Cortex, Hippocampus, Brainstem
α2
Clonidine Yohimbine Rauwolscine Prazosin
Cortex, Brainstem, Midbrain, Spinal cord
β1 Isoproteronol Terbutaline
Alprenolol Betaxolol Propranolol
Olfactory nucleus, cortex, cerebellum, brainstem, spinal cord
β2
Procaterol Zinterol
Propranolol Olfactory bulb, piriform cortex, hippocampus, cerebellum
β3
Pindolol Bupranolol Propranolol
NA pharmacology and localization
Adapted from Nestler, Hyman, Malenka 2008 – McGraw-Hill
NA Neuron
Nestler, Hyman, Malenka 2008– McGraw-Hill
NA transporter (NET)
• Re-uptake of NA from synaptic cleft • Similar structure to SERT, DAT • High levels of protein expression throughout
brain (projections, nerve terminals) • Drugs which inhibit/affect transport – can
promote/prolong NA signalling
• Antidepressants – high affinity for NET – venlafaxine, reboxetine – tricyclic antidepressants (desipramine,
nortryptiline)
• Cocaine – inhibits NET, SERT and DAT – and prevent the reuptake of 5HT, NA, DA
• Amphetamines: are taken up by transporters (NET, SERT, DAT), and then VMAT, leading to leakage of transmitter out of vesicles
Drugs inhibiting NET
Amphetamine actions
Interference with the NA system
• Activate / block receptors __________________ • Inhibit synthesis: ________________________ • Inhibit neuronal re-uptake: _________________ • Depletion: __________________________ • Inhibit metabolism: ________________________ • Promote release: __________________________
Common therapeutic drugs that affect NA in CNS?
• Antidepressants (TCAs, MAO Inhibitors, selective noradrenaline reuptake inhibitors)
• Stimulants – Methylphenidate (ADHD) – Amphetamines (ADHD, narcolepsy)
• NA synthesis inhibitors – Carbidopa (Parkinson’s)
Some adverse effects associated with modulating
NA system??
Summary
After this lecture (and with a bit of studying) you should be familiar with: • Synthetic & metabolic pathways for 5HT, NA • Main 5HT/NA pathways in CNS (to help
explain function) • Their roles in CNS function (normal and
abnormal) • Therapeutic use of drugs affecting 5HT, NA