Session ID: 1001 June 14, 2012

Transcription

1 It s Not Just Serotonin: Neurosignaling in Mental Illness Barbara J. Limandri, DNSc, APRN, BC Professor of Nursing Linfield College Learning Outcomes Distinguish between metabotropic and ionotropic neuroreceptors Identify the major neuroreceptors and neurotransmitters involved in mental illnesses Describe neurosignaling in the brain in relation to mental illness Discuss new targets for psychiatric drug therapies Disclosure Statement I have no commercial financial conflicts of interest to disclose I may discuss some off label use of medications as examples of treatment options Barbara J. Limandri, DNSc, APRN, BC 1

2 Agenda Synaptic Transmission Signal Transduction in the Brain Neurotransmitters Neuropharmacological Applications Synaptic Transmission Process of firing neurons to move a message between neurons and to different areas of the brain Neuron at rest is polarized by separating intracellular and extracellular ions High extracellular sodium, calcium and chloride High intracellular potassium Passive small amounts of ions flow without affecting the charge Maintains an equilibrium potential Action Potential Elements of the action potential Depolarization Repolarization Hyper polarization Voltage-gated sodium, calcium, and potassium channels generate the electrical signals through action potentials Sodium activates the signal Potassium ends the signal Calcium activates neurotransmitter release Barbara J. Limandri, DNSc, APRN, BC 2

3 Animation of Action Potential /channel.html Neurotransmission Once depolarization occurs, calcium channels open and calcium activates the synaptic vesicle to move to the terminal button and fuse with the neuron membrane This fusion releases the neurotransmitters into the synaptic space to find and bind with a neuroreceptor on the post synaptic neuron Once this occurs the second neuron is activated Animation of Neurotransmission /chp44/4403s.swf Barbara J. Limandri, DNSc, APRN, BC 3

4 Basic Receptor Types Ionotropic Receptors (ligand-gated ion channels) Five protein transmembrane subunits When ligand (neurotransmitter) binds with extracellular site, the subunits quickly open a pore through which ions pass Act quickly to depolarize neuron Metabotropic Receptors (G-protein-coupled) Metabotropic Receptors Seven protein transmembrane subunits without pore Ligand activates conformational change of the receptor causing the G-protein subunits to separate The G-protein replaced by GTP which activates the alpha subunit Alpha subunit undergoes conformation to then activate adenyl cyclase, which is converted to c-amp as a second messenger, which attaches to calcium ion channel to open Act to fire the neuron and then is inactivated by other proteins Animated MetabotropicReceptor fra&feature=related Barbara J. Limandri, DNSc, APRN, BC 4

5 Neurotransmitters Neurotransmitters (NT) Excitatory: can inhibit hyperpolarization, thereby causing additive changes to the membrane potential Inhibitory: inside of the cell becomes more negative causing hyperpolarization, thereby delaying another action potential Neurons can have vesicles containing different NT but in different concentrations Common Neurotransmitters Acetylcholine Dopamine Norepinephrine Epinephrine Serotonin Histamine Glutamate GABA Neuroreceptors The binding units for neurotransmitters There can be multiple subtypes of neuroreceptors Ligands act on neuroreceptors Barbara J. Limandri, DNSc, APRN, BC 5

6 Dopamine Receptors D-1 D-1 & D-2 receptors are synergistic D-2 Target of therapeutic & EPS effects of DA antagonists D-3 Unknown D-4 Target of Serotonin-Dopamine Antagonists D-5 Unknown Adrenergic Receptors α1a, B, D α2a, B, C β1 β2 β3 Antagonists antihypertensive Agonists sedative & antihypertensive Regulation of cardiac function Regulation of bronchial muscle contraction Regulation of adipose tissue function Histamine Receptors H-1 Antagonists produce sedation, weight gain H-2 Antagonists for peptic ulcer disease H-3 Antagonists produce arousal, appetite suppression Barbara J. Limandri, DNSc, APRN, BC 6

7 Serotonin Receptors 5HT-1A 5HT-1B 5HT-1D 5HT-1F 5HT-2A 5HT-2B 5HT-2C Antidepressant action; partial agonist is anxiolytic Possible role in locomotor activity, aggression Target of antimigraine drugs Target of antimigraine drugs Target of hallucinogens, SDAs Regulation of stomach contraction Regulation of appetite, anxiety, seizures; target of hallucinogens Serotonin Receptors Con t 5HT-3 5HT-4 5HT-6 5HT-7 5HT- 1E, 5HT-5a & b Antagonists antiemetic, anxiolytic, cognitive enhancement Modulation of cognition, anxiety Target of hallucinogens, SDAs Possible regulation of circadian rhythms Unknown Glutamate Metabotropic Receptors S Group I Group II Group III Increase NMDA receptor activity, possible agonist for treatment of GAD Decrease NMDA receptor activity, possible agonist to treat schizophrenia Decrease NMDA receptor activity, possible agonist to treat schizophrenia Barbara J. Limandri, DNSc, APRN, BC 7

8 Glutamate Ionotropic Receptors S AMPA NMDA Kainate Antagonists may treat epilepsy, agonists may treat neurodegenerative diseases Antagonists produce positive, negative & cognitive symptoms of schizophrenia Antagonists may have role in treatment of pain, migraine, epilepsy, stroke, & anxiety GABA-A Receptors GABA-A GABA-B Regulate neuronal excitability, responsible for rapid mood changes Mediate slow inhibitory potentials, effects memory and mood and pain response Neuropharmacological Applications Drugs are ligands, therefore they affect neurotransmission and neuroreception Expect to see more multi receptor drugs Drugs may have differential affects on receptor subtypes to produce different effects and adverse responses Newer drugs will target different neurotransmitters and receptors Barbara J. Limandri, DNSc, APRN, BC 8

9 Neuropharmacologic Applications Drugs in the pipeline: Glutamate antagonists for dementia, schizophrenia & addictions GSK Phase II 5HT-6 antagonist for dementia Novartis Agomelatine Phase III 5HT-2 antagonist & agonist for melatonin 1 & 2 for treatment of depression Novartis Emapunil, Phase III selective agonist of BZD receptor site of GABA for treatment of anxiety & panic AstraZeneca Mecamylamine, Phase III neuronal nicotinic modulator to treat depression & anxiety Drugs in the Pipeline AstraZeneca Phase II NMDA channel blocker for treatment resistant depression AstraZeneca Phase II α4β2 nicotinic receptor modulator as adjunct to donepezil for Alzheimer s disease AstraZeneca Phase II histamine 3 antagonist for Alzheimer s disease Drugs in the Pipeline Lilly Pomaglumetad Methionil, Phase III agonist of metabotropic glutamate II/III for treatment of schizophrenia Lilly Edovoxetine, Phase III norepinephrine reuptake inhibitor for treatment of depression and ADD Lilly Solanezumab, Phase III binds to soluable amyloid β for treatment of Alzheimer s Barbara J. Limandri, DNSc, APRN, BC 9

10 Drugs in the Pipeline Merck Suvorexant, Phase III orexin receptor antagonist for treatment of insomnia Roche, Phase II metabotropic glutamate II antagonist for treatment of depression Roche, bitopertin, Phase III glycine reuptake inhibitor to enhance NMDA activity to treat schizophrenia Roche, Phase II metabotropic glutamate receptor 5 modulator for treatment of depression and autism Barbara J. Limandri, DNSc, APRN, BC 10