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 1

Cardiac Ganglion Preganglionic neuron Postganglionic neuron Target Target 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  PACAP38, PACAP27  Locally-generated signals PACAP 1-27 28-38  Nitric Oxide (NO)  Inflammatory signals 2

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 Model System  Guinea pig cardiac ganglion Mawe, et al (1996) Cell Tissue Res 285:281. 3

MAP2 Substance P Histamine PACAP 27 MAP2 MAP2 4

Guinea pig cardiac ganglion Nitric Oxide in the Heart “puffer” containing test substance 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 Histamine Depolarization Mechanism? 5

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) 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 6

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 PACAP 7

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? 8

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 ¡ IHC - % nNOS Neurons qPCR – nNOS mRNA 4.5 ¡ 25 Control Rela9ve ¡Change ¡in ¡mRNA ¡Expression ¡ 4 ¡ MI # Sham surgery 20 3.5 ¡ 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 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 9

What could produce this change in synaptic function? 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 10

Adrenergic Blocker: Timolol Adrenergic Blocker: Timolol MI Time Course MI Time Course  Induce MI  Examine tissue at  4 Days  7 Days  14 Days 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 11

The Heart Nebula…….. 12