of the Heart Jean Hardwick Ithaca College Loewi, O. (1921). On the - PDF document

Otto Loewi – “ Vagusstoff” Neural Regulation of the Heart Jean Hardwick Ithaca College Loewi, O. (1921). On the humoral propagation of cardiac nerve action. Pflugers Arch. 189 : 239-242. Control of Heart Rate http://www.studyblue.com/notes/note/n/excitable- cells/deck/6733976 http://humanphysiology2011.wikispaces.com/ 06.+Cardiology 1

http:// humanphysiology2011.wikispaces.co m/06.+Cardiology Cardiac Ganglion Preganglionic neuron Postganglionic neuron Target Target 2

Sensory innervation CNS Preganglionic Neurons Sensory Inputs • BP Sympathetic Postganglionic • pH Fibers • pO 2 Parasympathetic Postganglionic Neurons Cardiac Sensory Neurons Cardiac Target Cells Parasympathetic Cardiac Ganglion Neuropeptides § Neuropeptides § Fast synaptic transmission (ionotropic) § Sensory peptides (sensory neurons from spinal § ACh (nicotinic receptors) cord) § Other signals (metabotropic) § Substance P § CGRP § ACh (muscarinic receptors) § PACAP (neurons from brainstem, neurons within § NE ganglion) § Neuropeptides § Locally-generated signals § Nitric Oxide (NO) § Inflammatory signals 3

Nitric Oxide Nitric Oxide NOS § Three isoforms of nitric oxide synthase Ca ++ § Neuronal NOS (nNOS) § Endothelial NOS (eNOS) NO § Inducible NOS (iNOS) Guanylate Cyclase cGMP Cardiac Mast Cells Parasympathetic Cardiac Ganglion § Found in high density in mammalian heart § Stimulated by: Mast cells Preganglionic Fibers § Antigen exposure Postganglionic Fibers § Sensory neuropeptides § Chemoreceptors Sympathetic § pH changes, low oxygen Postganglionic Fibers § Upon stimulation, release § Histamine § Prostaglandins Sensory Afferents 4

Model System § Guinea pig cardiac ganglion Mawe, et al (1996) Cell Tissue Res 285:281. 5

MAP2 Substance P Histamine PACAP 27 MAP2 MAP2 6

Guinea pig cardiac ganglion Nitric Oxide in the Heart “puffer” containing test substance nNOS MAP2 Neuromodulation § Acute changes § Changes in excitability Preganglionic fiber § Changes in sensitivity to individual chemicals Postganglionic neuron § Changes in synaptic function § Long term changes Phasic Neuron Tonic Neuron § Changes in phenotype 7

Histamine Depolarization Mechanism? Sodium Channels: Ion substitution Membrane Depolarization Amplitude Duration N Control Control 5.6 ± 2.8 46.9 ± 29.4 19 14 Histamine, 12 # # AP Frequency (Hz) 50% NMG 4.0 ± 1.5 54.3 ± 18.4 6 10 # # 8 100% NMG 2.0 ± 1.1 33.9 ± 35.1 9 # 6 # 4 2 0 0.0 0.2 0.4 0.6 Stimulus (nA) 8

Excitability Changes: Ion Channel Inhibitors § Barium § How can you change the firing § Blocks many K channels, including some properties of a neuron? leakage channels and m-current § 4-aminopyridine § What ionic mechanisms could § Blocks A-current (K channel) produce this? § TEA § Blocks some Ca-dependent K channels § Cs § Blocks H-current (hyperpolarization- activated cation channel) Control Cs + Ba 2+ 4-AP 1 mM 4-AP 1 mM Cs + 5 mM TEA 1 mM Ba 2+ TEA 9

Muscarinic Receptors Remove § Preganglionic fibers (from brainstem) external Ca 2+ § ACh - nicotinic (fast) and muscarinic (slow) § Bethanechol – muscarinic agonist Control 200 µ M Cd 2+ Beth Adrenergic Receptors Single Action Potentials § Adrenergic postganglionic fibers § NE – increase excitability Control NE 10

PACAP 11

Synaptic Function Excitability Changes § Histamine § Dependent on influx of extracellular Calcium ions § TRPC channel? § Muscarinic (bethanechol) § TEA-sensitive channels § BK channels? M-current? § Adrenergic Preganglionic fiber § Calcium-dependent § Indirect inhibition of BK channels? Postganglionic neuron § VDCC? § Neuropeptides § PACAP § H channels, Calcium-dependent mechanism Long term changes: Remodeling Synaptic Transmission § Nitric Oxide § Chronic heart disease § Number one cause of death in the United EPSP States Amp (mV) § 2010 data: 595,444 deaths due to heart disease 4.1 + 1.6 Control § ~24% of all deaths (N=6) § Ischemic heart disease (heart attacks) most common form 7.4 + 3.5 * SNP (N=6) How does neuronal control of the heart change with chronic heart * p < 0.02, paired T test disease? 12

Models of Heart Disease Regulation of NOS levels § Myocardial infarction (MI) § Ligate left ventricular coronary artery § 6-9 weeks recovery § Pressure Overload (PO) § Band descending dorsal aorta § Produces left ventricular hypertrophy § 8-10 weeks recovery Control Chronic MI § Sham surgery nNOS Horackova, M. et al. (2004) Am J Physiol Heart Circ Physiol 287: and H1599-H1608 MAP2 Regulation of NOS levels Synaptic Function 5 ¡ qPCR – nNOS mRNA IHC - % nNOS Neurons 4.5 ¡ 25 Rela9ve ¡Change ¡in ¡mRNA ¡Expression ¡ 4 ¡ Control MI # Sham surgery 3.5 ¡ 20 PO # 3 ¡ %nNOS cells 15 2.5 ¡ 2 ¡ 10 1.5 ¡ 1 ¡ Preganglionic fiber 5 0.5 ¡ 0 ¡ 0 Control ¡ Sham ¡ MI ¡ PO ¡ Postganglionic neuron 13

Synaptic Function Synaptic Function • EPSPs • Suprathreshold stimulations • 20 Hz, 2 sec duration CONTROL MI PO FTS 20 Hz RMP (mV) -49.5 ± 7.9 -41.8 ± 5.8 -46.7 ± 9.1 EPSP amplitude (mV) 6.8 ± 0.4 6.6 ± 0.6 5.6 ± 0.8 N 17 19 17 No significant differences What could produce this change in synaptic function? 14

Synaptic Changes § No changes in EPSP amplitudes with chronic disease § No apparent changes in synaptic function in animals with MI § Enhanced synaptic function ONLY in animals with PO § Increased function is not inhibited by atropine (not due to increased sensitivity to muscarinic activity) Drug Treatment Drug Treatment § Implant osmotic pump § NE blocker § Induce heart disease § Timolol § Blocks β -adrenergic § 2 weeks later, implant receptors pump § Total drug treatment period of 6 weeks § Control animals, just drug, no disease 15

Adrenergic Blocker: Timolol Adrenergic Blocker: Timolol MI Time Course MI Time Course § Induce MI § Examine tissue at § 4 Days § 7 Days § 14 Days 16

Student Collaborators Acknowledgements § National Institutes of Health § Heart, Lung, and Blood Institute Shannon Ryan ‘12, Kristen Levin ’12, § Rod Parsons - UVM Natasha Petersen ‘12, Rich Kintzing ‘12 § Jeffrey Ardell – ETSU Chris Palmer ‘11, Samantha Corrado ‘11, Phil Feinberg ‘11 § Marie Southerland, DVM – ETSU Not Pictured: Caitlin Baran ‘09 Lauren Houdek ’09 Stephanie Hinsvark ‘12 Melanie Powers Fraites ‘01, Ally Girasole ‘10 The Heart Nebula…….. 17