Towards a clearer view of sympathetic innervation of cardiac and skeletal muscles

doi:10.1016/j.pbiomolbio.2019.07.003

Progress in Biophysics and Molecular Biology

Volume 154, August 2020, Pages 80-93

https://doi.org/10.1016/j.pbiomolbio.2019.07.003 Get rights and content

Abstract

It is well appreciated that autonomic neurons have a central role in the homeostatic regulation of organs and systems and participate to the pathogenesis of several disease conditions. As such, the function and signalling pathways activated by sympathetic neurons (SNs) in different cell types and organs have become a matter of intense investigation throughout the years of modern biomedical research. This review is focused on the methods used to address sympathetic innervation of cardiac and skeletal muscles which, quite surprisingly, has remained incompletely understood, mainly due to the technical limitations of the traditional methodologies. The current review provides a summary of the existing literature and, putting together the results obtained with different methodological approaches, provides a comprehensive view of the complexity of the SN network in striated muscles.

Introduction

The autonomic nervous system (ANS) finely regulates a large spectrum of involuntary body functions, including heart rate (HR) and contraction, as well as respiratory rate and, vasomotor activity. As part of the peripheral nervous system, the ANS includes two anatomically distinct branches, namely: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PSN), which commonly operate opposite effects in the target organs (Karemaker, 2017). In fact, the main function of the PSN, which in humans is dominant at rest, is to maintain organ homeostasis. On the contrary, the SNS, which will be the object of this review, is central for the organism adaptation to stresses, and its maximal activation is well described by the series of effects elicited in various organs and systems during the ‘fight-or-flight’ response. From an anatomic point of view, the ANS contains afferent fibers, which relay external (environmental) and internal (physiologic parameters, organ function) inputs, as well as efferent fibers, which actuate the adequate response to either type of sensory stimuli. The efferent part of the ANS is made by two-neuron series (pre-ganglionic neuron and post-ganglionic neuron). The cell bodies of pre-ganglionic neurons are located in specific regions of the central nervous system (CNS), and their terminal portions synapse with post-ganglionic neurons, whose cell bodies, for the SNS, organize in paravertebral ganglia, adjacent to the spinal column. These include: 3 cervical (superior, middle, and inferior), 12 thoracic, 4 lumbar and 5 sacral ganglia (Waxenbaum and Varacallo, 2019). The sympathetic axons that originate from these stations, once reached the target organs, ramify in multiple processes which run through the interstitium, displaying the typical ‘pearl-necklace’ morphology, characterized by regularly distributed varicosities, where neurotransmitter-containing vesicles are stored. The SNS acts mainly through the release of noradrenaline (NE) and neuropeptide Y (NPY), and the consequent activation of α-/β-adrenoceptors (ARs) or NPY-receptors (NPY-Rs), expressed by target cells (Ciccarelli et al., 2013a; De Angelis et al., 2019; Smolen, 1988). As stated above, the SNS is known, to the entire scientific community, as an alarm and defence system, allowing the organism to react rapidly and efficiently to intrinsic (e.g. hemorrage) or extrinsic (e.g. life-threatening events) stresses. When this happens, the SNS activates a number of well-orchestrated actions, including vasoconstriction, increase in cardiac frequency and contractile force, enhanced blood flow to muscles and metabolic energy availability. However, the SNS is in constant operation also in non-stressful situations, as it modulates, e.g. HR on a beat-to-beat basis, and regulates the normal respiratory cycle (Franzoso et al., 2016). Due to its widespread functions, sympathetic neurons (SNs) are present in every tissue in the body, making the SNS the most abundant component of the ANS (Waxenbaum and Varacallo, 2019). This review will focus on the SNS innervating the cardiac and skeletal muscles.

Section snippets

Overview of the cardiac sympathetic nervous system

The post-ganglionic SNs innervating the heart originate mainly from the cervical, stellate and, the first thoracic ganglia. Their axons reach the heart surface (i.e. epicardium), at several different sites, and penetrate the myocardial interstitium, using blood vessels as topographic cues (Franzoso et al., 2016). It is understood that SNs are highly represented in the sino-atrial node (SAN) where NE, discharged during stress, leads to an increase in HR (i.e. positive chronotropic effect). SNs

The pioneering studies of heart innervation

The earliest studies, that addressed heart innervation, used bright-field microscopy, and allowed demonstrate the presence of nerve processes inside the myocardium in frogs and other vertebrates (Miller and Kasahara, 1964; Woollard, 1926) (Fig. 1A). These results stimulated researches to better define the gross anatomy of cardiac SNS, which was investigated in hearts processed with Methylene blue, which allowed for the identification of neurons and their cytoplasmic ramifications (Barbosa and

The elusive sympathetic innervation of skeletal muscle

It is well-accepted that acetylcholine (ACh), released by motor neurons (MNs) at the neuro-muscular junction (NMJ) interacts with nicotinic receptors, triggering skeletal myocyte contraction, and mediates, in the long term, transcriptional effects (Liu et al., 2005; Schiaffino, 2010). A body of evidence indicates that, in parallel, signalling depending on muscular β2-ARs plays a key role in the maintenance of muscle homeostasis, by modulating myocyte force generation (Arreola et al., 1987;

Conclusions

In this manuscript, we presented an overview of different studies, which in time, aimed at characterizing the topology and structural organization of the SNS innervating two striated muscles: the heart and skeletal muscle. While in the heart, the overall role of SNs in the regulation of contractile function and rate was somewhat clear from the early studies, skeletal muscle sympathetic innervation is still object of investigation. What can be extrapolated from the literature is that SNS

Disclosures

Nothing to declare.

Funding

This work was supported by the University of Padova (SID-2017) and AriSLA (SNop) to TZ.

Acknowledgements

We are grateful to Prof. Marco Mongillo for critical reading, and Dr Ellen Jane Corcoran for checking language.

References (224)

E. Agduhr
Sympathetic innervation of the muscles of the extremities. A histo-experimental study
Verhand. Akad. Wetensch.
(1920)
J.Y. Altarejos et al.
CREB and the CRTC co-activators: sensors for hormonal and metabolic signals
Nat. Rev. Mol. Cell Biol.
(2011)
R.H. Anderson
Histologic and histochemical evidence concerning the presence of morphologically distinct cellular zones within the rabbit atrioventricular node
Anat. Rec.
(1972)
J.A. Armour et al.
Gross and microscopic anatomy of the human intrinsic cardiac nervous system
Anat. Rec.
(1997)
J. Arreola et al.
Modulation of calcium channels of twitch skeletal muscle fibres of the frog by adrenaline and cyclic adenosine monophosphate
J. Physiol.
(1987)
A.V.N. Bacurau et al.
Sympathetic hyperactivity differentially affects skeletal muscle mass in developing heart failure: role of exercise training
J. Appl. Physiol.
(2009)
B.Q. Banker et al.
The ultrastructural features of the mammalian muscle spindle
J. Neuropathol. Exp. Neurol.
(1971)
P. Barbosa et al.
The effects of vital dyes on living organisms with special reference to methylene blue and neutral red
Histochem. J.
(1971)
D. Barker
The innervation of the muscle-spindle
Q. J. Microsc. Sci.
(1948)
D. Barker et al.
Autonomic innervation of receptors and muscle fibres in cat skeletal muscle
Proc. R. Soc. Lond. Ser. B Biol. Sci.
(1981)

M.I. Baxter et al.

Features of the nervous system and heart of archachatina revealed by the electron microscope and by electrophysiological recording

J. Molluscan Stud.

(1963)

J.A. Beavo et al.

Cyclic nucleotide research -- still expanding after half a century

Nat. Rev. Mol. Cell Biol.

(2002)

K. Becker et al.

Chemical clearing and dehydration of GFP expressing mouse brains

PLoS One

(2012)

D. Beitzke et al.

Assessment of sympathetic reinnervation after cardiac transplantation using hybrid cardiac PET/MRI: a pilot study

J. Magn. Reson. Imaging

(2019)

F.M. Bengel

Imaging targets of the sympathetic nervous system of the heart: translational considerations

J. Nucl. Med.

(2011)

F.M. Bengel et al.

Kinetics of 123I-MIBG after acute myocardial infarction and reperfusion therapy

J. Nucl. Med.

(1999)

J. Boeke

Die morphologische Grundlage der sympathischen Innervation der quergestreiften Muskelfasern

Z. Mikrosk.-Anat. Forsch. (Leipz.)

(1927)

J. Boeke

Die doppelte (motorische und sympathische) efferente Innervation der quergestreiften Muskelfasern

Anat. Anz

(1913)

J. Boeke

Die motorische Endplatte bei den höheren Vertebraten, ihre Entwickelung, Form und Zusammenhang mit der Muskelfaser

Anat. Anz

(1909)

J. Boeke

Ueber eine aus marklosen Fasern hervorgehende zweite Art von hypolemmalen Nervenendplatten bei den quergestreiften Muskelfasern der Vertebraten

Anat. Anz

(1909)

N.E. Boutagy et al.

Recent advances and clinical applications of PET cardiac autonomic nervous system imaging

Curr. Cardiol. Rep.

(2017)

K.E. Brack

The heart's “little brain” controlling cardiac function in the rabbit

Exp. Physiol.

(2015)

L. Bremer

Ueber die Muskelspindeln nebst Bemerkungen über Structur, Neubildung und Innervation der quergestreiften Muskelfaser

Arch. für mikroskopische Anat.

(1883)

L. Bremer

Ueber die Endigungen der markhaltigen und marklosen Nerven im quergestreiften Muskel

Arch. für mikroskopische Anat.

(1882)

L. Bremer

Die Nerven der Capillaren, der kleineren Arterien und Venen

Arch. für mikroskopische Anat.

(1882)

H. Bulow et al.

Myocardial presynaptic sympathetic innervation evaluated with C-11-HED-PET in patients with severe coronary artery disease but no history of myocardial infarction

H.P. Bulow et al.

Alterations of myocardial presynaptic sympathetic innervation in patients with multi-vessel coronary artery disease but without history of myocardial infarction

Nucl. Med. Commun.

(2003)

S.P. Cairns et al.

β-Adrenergic potentiation of E–C coupling increases force in rat skeletal muscle

Muscle Nerve

(1993)

S.P. Cairns et al.

The effects of beta-adrenoceptor activation on contraction in isolated fast- and slow-twitch skeletal muscle fibres of the rat

Br. J. Pharmacol.

(1993)

P.G. Camici

Advances in SPECT and PET for the management of heart failure

Heart

(2010)

V. Chan-Palay et al.

Synthesizing enzymes for four neuroactive substances in motor neurons and neuromuscular junctions: light and electron microscopic immunocytochemistry

Proc. Natl. Acad. Sci. U.S.A.

(1982)

V. Chan-Palay et al.

Coexistence in human and primate neuromuscular junctions of enzymes synthesizing acetylcholine, catecholamine, taurine, and gamma-aminobutyric acid

Proc. Natl. Acad. Sci. U.S.A.

(1982)

C.J. Chang et al.

Electron microscopic studies of microvasculature and sympathetic nerve fibers in dilated cardiomyopathy

Chin. Med. J.

(1998)

X. Chen et al.

Radionuclide imaging of neurohormonal system of the heart

Theranostics

(2015)

T. Chiba et al.

On the fine structure of the nerve terminals in the human myocardium

Z. Zellforsch. Mikrosk. Anat.

(1970)

J.K. Choate et al.

Sympathetic and parasympathetic neuromuscular junctions in the Guinea-pig sino-atrial node

J. Auton. Nerv. Syst.

(1993)

L.T. Chow et al.

Autonomic innervation of the human cardiac conduction system: changes from infancy to senility--an immunohistochemical and histochemical analysis

Anat. Rec.

(2001)

L.T. Chow et al.

The innervation of the human myocardium at birth

J. Anat.

(1995)

L.T. Chow et al.

Innervation of the human cardiac conduction system at birth

Br. Heart J.

(1993)

K. Chung et al.

Structural and molecular interrogation of intact biological systems

Nature

(2013)

M. Ciccarelli et al.

Adrenergic receptors and metabolism: role in development of cardiovascular disease

Front. Physiol.

(2013)

M. Ciccarelli et al.

Endothelial G protein-coupled receptor kinase 2 regulates vascular homeostasis through the control of free radical oxygen species

Arterioscler. Thromb. Vasc. Biol.

(2013)

L. Conforti et al.

Influence of sympathetic innervation on the membrane electrical properties of neonatal rat cardiomyocytes in culture

J. Dev. Physiol.

(1991)

J.H. Coote

The organisation of cardiovascular neurons in the spinal cord

Rev. Physiol. Biochem. Pharmacol.

(1988)

J.H. Coote et al.

Intracellular recordings from sympathetic preganglionic neurones

Neurosci. Lett.

(1979)

I. Costantini et al.

A versatile clearing agent for multi-modal brain imaging

Sci. Rep.

(2015)

S.J. Crick et al.

A quantitative study of nerve distribution in the conduction system of the Guinea pig heart

J. Anat.

(1996)

S.J. Crick et al.

Innervation of the human cardiac conduction system: a quantitative immunohistochemical and histochemical study

Circulation

(1994)

D.K. Dastur et al.

Fine structure of A: autonomic nerve fibers and terminals in human myocardium; and B: myocardial changes in congenital heart disease

Ultrastruct. Pathol.

(1989)

F. Davies et al.

Neurological studies of the cardiac ventricles of mammals

J. Anat.

(1952)

Cited by (21)

Remodelling of potassium currents underlies arrhythmic action potential prolongation under beta-adrenergic stimulation in hypertrophic cardiomyopathy
2022, Journal of Molecular and Cellular Cardiology
Citation Excerpt :
Moreover, since we did not perform simulations at tissue or organ level, dispersion of repolarisation was surrogated as an APD difference of isolated cells. This is an estimation of the repolarisation gradient, which is also affected by elements not present in this study, as the cellular electrotonic coupling or the heterogeneous distribution of the sympathetic innervation system [56]. Human HCM cardiomyocyte data is also scarce, and typically only available from obstructive patients undergoing surgical myectomy.
Hypertrophic cardiomyopathy (HCM) patients often present an enhanced arrhythmogenicity that can lead to lethal arrhythmias, especially during exercise. Recent studies have indicated an abnormal response of HCM cardiomyocytes to β-adrenergic receptor stimulation (β-ARS), with prolongation of their action potential rather than shortening. The mechanisms underlying this aberrant response to sympathetic stimulation and its possible proarrhythmic role remain unknown. The aims of this study are to investigate the key ionic mechanisms underlying the HCM abnormal response to β-ARS and the resultant repolarisation abnormalities using human-based experimental and computational methodologies. We integrated and calibrated the latest models of human ventricular electrophysiology and β-ARS using experimental measurements of human adult cardiomyocytes from control and HCM patients. Our major findings include: (1) the developed in silico models of β-ARS capture the behaviour observed in the experimental data, including the aberrant response of HCM cardiomyocytes to β-ARS; (2) the reduced increase of potassium currents under β-ARS was identified as the main mechanism of action potential prolongation in HCM, rather than a more sustained inward calcium current; (3) action potential duration differences between healthy and HCM cardiomyocytes were increased upon β-ARS, while endocardial to epicardial differences in HCM cardiomyocytes were reduced; (4) models presenting repolarisation abnormalities were characterised by downregulation of the rapid delayed rectifier potassium current and the sodium‑potassium pump, while inward currents were upregulated. In conclusion, our results identify causal relationships between the HCM phenotype and its arrhythmogenic response to β-ARS through the downregulation of potassium currents.
Running skeletal muscle clocks on time— the determining factors
2022, Experimental Cell Research
Citation Excerpt :
The SNS is a well-known mediator of SCN signals in many tissues, such as the skin; in fact, ocular light stimulation activates the sympathetic nervous system and promotes hair regeneration by increasing cutaneous norepinephrine release [107]. Ablation of the SNS shows a significant effect on muscle growth and maintenance, suggesting that the SNS plays a role in skeletal muscle homeostasis [108–110]. Whether the SCN can communicate with muscle tissue through the SNS has not yet been studied and is an open question in the field.
Circadian rhythms generate 24 h-long oscillations, which are key regulators of many aspects of behavior and physiology. Recent circadian transcriptome studies have discovered rhythmicity at the transcriptional level of hundreds of skeletal muscle genes, with roles in skeletal muscle growth, maintenance, and metabolic functions. These rhythms allow this tissue to perform molecular functions at the appropriate time of the day in order to anticipate environmental changes. However, while the last decade of research has characterized several aspects of the skeletal muscle molecular clock, many still are unexplored, including its functions, regulatory mechanisms, and interactions with other tissues. The central clock is believed to be located in the suprachiasmatic nucleus (SCN) of the brain hypothalamus, providing entrainment to peripheral organs through humoral and neuronal signals. However, these mechanisms of action are still unknown. Conversely, muscle tissue can be entrained through extrinsic, SCN-independent factors, such as feeding and physical activity. In this review, we provide an overview of the recent research about the extrinsic and intrinsic factors required for skeletal muscle clock regulation. Furthermore, we discuss the need for future studies to elucidate the mechanisms behind this regulation, which will in turn help dissect the role of circadian disruption at the onset of aging and diseases.
Optical clearing in cardiac imaging: A comparative study
2022, Progress in Biophysics and Molecular Biology
Citation Excerpt :
Initially, all tissue transformation methodologies have been settled and applied in neuroscience, to successfully image and study the brain (Silvestri et al., 2016). However, compared to cerebral tissue, cardiac tissue displays a number of differences, e.g. the high concentration of myoglobin that increases significantly tissue coloration and thus optical absorption in the range of visible wavelengths (Di Bona et al., 2020). Therefore, the application of the original protocols does not perform as efficiently on cardiac tissue as on the brain, and has been mainly used for the 3D investigation of small portions of the heart (Pianca et al., 2019; Olianti et al., 2020).
The optical clearing of the cardiac tissue has always been a challenging goal to obtain successful three-dimensional reconstructions of entire hearts. Typically, the developed protocols are targeted at the clearing of the brain; cardiac tissue requires proper arrangements to the original protocols, which are usually tough and time-consuming to figure out. Here, we present the application of three different clearing methodologies on mouse hearts: uDISCO, CLARITY, and SHIELD. For each approach, we describe the required optimizations that we have developed to improve the outcome; in particular, we focus on comparing the features of the tissue after the application of each methodology, especially in terms of tissue preservation, transparency, and staining. We found that the uDISCO protocol induces strong fiber delamination of the cardiac tissue, thus reducing the reliability of structural analyses. The CLARITY protocol confers a high level of transparency to the heart and allows deep penetration of the fluorescent dyes; however, it requires long times for the clearing and the tissue loses its robustness. The SHIELD methodology, indeed, is very promising for tissue maintenance since it preserves its consistency and provides ideal transparency, but further approaches are needed to obtain homogeneous staining of the whole heart. Since the CLARITY procedure, despite the disadvantages in terms of tissue preservation and timings, is actually the most suitable approach to image labeled samples in depth, we optimized and performed the methodology also on human cardiac tissue from control hearts and hearts with hypertrophic cardiomyopathy.
Novel optics-based approaches for cardiac electrophysiology
2020, Progress in Biophysics and Molecular Biology
Sympathetic System in Wound Healing: Multistage Control in Normal and Diabetic Skin
2023, International Journal of Molecular Sciences
Sympathetic neuropathology is revealed in muscles affected by amyotrophic lateral sclerosis
2023, Frontiers in Physiology

View all citing articles on Scopus

¹: equal contribution.

View full text

Towards a clearer view of sympathetic innervation of cardiac and skeletal muscles

Abstract

Introduction

Section snippets

Overview of the cardiac sympathetic nervous system

The pioneering studies of heart innervation

The elusive sympathetic innervation of skeletal muscle

Conclusions

Disclosures

Funding

Acknowledgements

Sympathetic innervation of the muscles of the extremities. A histo-experimental study

Verhand. Akad. Wetensch.

CREB and the CRTC co-activators: sensors for hormonal and metabolic signals

Nat. Rev. Mol. Cell Biol.

Histologic and histochemical evidence concerning the presence of morphologically distinct cellular zones within the rabbit atrioventricular node

Anat. Rec.

Gross and microscopic anatomy of the human intrinsic cardiac nervous system

Anat. Rec.

Modulation of calcium channels of twitch skeletal muscle fibres of the frog by adrenaline and cyclic adenosine monophosphate

J. Physiol.

Sympathetic hyperactivity differentially affects skeletal muscle mass in developing heart failure: role of exercise training

J. Appl. Physiol.

The ultrastructural features of the mammalian muscle spindle

J. Neuropathol. Exp. Neurol.

The effects of vital dyes on living organisms with special reference to methylene blue and neutral red

Histochem. J.

The innervation of the muscle-spindle

Q. J. Microsc. Sci.

Autonomic innervation of receptors and muscle fibres in cat skeletal muscle

Proc. R. Soc. Lond. Ser. B Biol. Sci.

Features of the nervous system and heart of archachatina revealed by the electron microscope and by electrophysiological recording

J. Molluscan Stud.

Cyclic nucleotide research -- still expanding after half a century

Nat. Rev. Mol. Cell Biol.

Chemical clearing and dehydration of GFP expressing mouse brains

PLoS One

Assessment of sympathetic reinnervation after cardiac transplantation using hybrid cardiac PET/MRI: a pilot study

J. Magn. Reson. Imaging

Imaging targets of the sympathetic nervous system of the heart: translational considerations

J. Nucl. Med.

Kinetics of 123I-MIBG after acute myocardial infarction and reperfusion therapy

J. Nucl. Med.

Die morphologische Grundlage der sympathischen Innervation der quergestreiften Muskelfasern

Z. Mikrosk.-Anat. Forsch. (Leipz.)

Die doppelte (motorische und sympathische) efferente Innervation der quergestreiften Muskelfasern

Anat. Anz

Die motorische Endplatte bei den höheren Vertebraten, ihre Entwickelung, Form und Zusammenhang mit der Muskelfaser

Anat. Anz

Ueber eine aus marklosen Fasern hervorgehende zweite Art von hypolemmalen Nervenendplatten bei den quergestreiften Muskelfasern der Vertebraten

Anat. Anz

Recent advances and clinical applications of PET cardiac autonomic nervous system imaging

Curr. Cardiol. Rep.

The heart's “little brain” controlling cardiac function in the rabbit

Exp. Physiol.

Ueber die Muskelspindeln nebst Bemerkungen über Structur, Neubildung und Innervation der quergestreiften Muskelfaser

Arch. für mikroskopische Anat.

Ueber die Endigungen der markhaltigen und marklosen Nerven im quergestreiften Muskel

Arch. für mikroskopische Anat.

Die Nerven der Capillaren, der kleineren Arterien und Venen

Arch. für mikroskopische Anat.

Myocardial presynaptic sympathetic innervation evaluated with C-11-HED-PET in patients with severe coronary artery disease but no history of myocardial infarction

Alterations of myocardial presynaptic sympathetic innervation in patients with multi-vessel coronary artery disease but without history of myocardial infarction

Nucl. Med. Commun.

β-Adrenergic potentiation of E–C coupling increases force in rat skeletal muscle

Muscle Nerve

The effects of beta-adrenoceptor activation on contraction in isolated fast- and slow-twitch skeletal muscle fibres of the rat

Br. J. Pharmacol.

Advances in SPECT and PET for the management of heart failure

Heart

Synthesizing enzymes for four neuroactive substances in motor neurons and neuromuscular junctions: light and electron microscopic immunocytochemistry

Proc. Natl. Acad. Sci. U.S.A.

Coexistence in human and primate neuromuscular junctions of enzymes synthesizing acetylcholine, catecholamine, taurine, and gamma-aminobutyric acid

Proc. Natl. Acad. Sci. U.S.A.

Electron microscopic studies of microvasculature and sympathetic nerve fibers in dilated cardiomyopathy

Chin. Med. J.

Radionuclide imaging of neurohormonal system of the heart

Theranostics

On the fine structure of the nerve terminals in the human myocardium

Z. Zellforsch. Mikrosk. Anat.