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AUTONOMIC CONTROL OF THE VERTEBRATE HEART

E.W. (Ted) Taylor, School of Biosciences,

University of Birmingham UK

The Golden Rule of Vaudeville:

Always put a comedy act on last and maybe finish with a comic song.

So this is it!

“Hello folks/Bom dia gentes!”

Brasil (1999-now) with Tobias to work with Augusto

2 beers Wang

“I distrust camels, and anyone else who can go a week without a drink” Joe Lewis

Denis Augusto Wilfried Homer Neto

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ACh receptors Nicotinic receptors in the autonomic nervous system can be blocked by hexamethonium

Nicotinic receptors on the skeletal muscle can be blocked by curare

Muscarinic receptors on the heart can be blocked by atropine

Adrenergic receptors β receptors can be blocked by propranolol, or stimulated by isoproteronol

α receptors can be blocked by phentolamine or stimulated by phenylephrine stimulators are “agonists” blockers “antagonists”

NE noradrenaline

Ach acetylcholine

Pharmacology of ANS

Taylor and Wang 2009

Phylogeny of Cardiac Innervation

CONTROL OF THE HEART and of CARDIO-RESPIRATORY INTERACTIONS

The sympathetic nervous system is primarily responsible for increases in heart rate in emergencies the “fight or flight response” or in “stressed”animals. It does not exert beat-to-beat control of the heart.

The parasympathetic nervous system exerts a dominant role in the tonic control of the heart and can exert beat-to-beat control that generates heart rarte variability (HRV) including changes in heart rate in phase with ventilation or cardiorespiratory interaction (CRI).

This control is exerted via the Xth cranial nerve, the vagus.

THIS IS OUR PRIMARY INTEREST!

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CARDIORESPIRATORY INTERACTIONS

We are investigating:

• 

• the evolution of the mechanisms for nervous control of the heart in vertebrates using classic physiological and neuro-anatomical techniques .

• 

• the roles of “feed-forward control” from the central nervous system (CNS) and of reflex or “feedback control” from peripheral receptors in determining heart rate variability (HRV) and in particular cardiorespiratory interactions (CRI).

MAMMALS In healthy mammals (e.g Marina!) heart rate increases during inspiration, a phenomenon known as:

respiratory sinus arrythmia (RSA)

MAMÍFEROS

Em mamíferos saudáveis, a freqüência cardíaca aumenta durante a inspiração, fenômeno conhecido como:

Arritmia sinusal respiratoria (RSA)

RSA developes in utero in human babies

It is present at full-term (40 weeks) but absent in premature babies (< 30 weeks)

It can be detected by Power Spectral Analysis (PSA)

RSA desenvolve-se dentro do útero em bebês humanos

Ele está presente durante 40 semanas, mas é ausente em bebês prematuros (menos de 30 semanas)

Pode ser detectado por Power Spectral Analysis (PSA)

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Power spectral analysis of heart rate variability (HRV) reveals respiratory sinus arrythmia (RSA) in the human neonate

Thompson, Brown, Gee and Taylor (1993) Early Human Devel. 31, 217-228

Premature babies in intensive care were monitored (from the back of the hospital equipment) with HRV and breathing movements recorded to a pc for power spectral analysis

Bebês prematuros foram monitorados com HRV tendo os movimentos respiratórios registrados num pc

The onset of RSA: Premature babies were born without a respiratory peak in the HRV power spectrum - A

This appeared at 33-36 weeks as ventilation became more regular - B, C

Babies compromised at birth often did not develop RSA (cot death?)

30 wks

33 wks

36 wks

Taylor, Leite and Skovgaard (2010) Braz. J. Med. Biol. Res. 43, 600.

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The mechanism:

Activity in cardiac vagal efferent (CVE) fibres is gated during inspiration, including their response to baroreceptor stimulation, leading to respiratory sinus arrythmia (RSA) A atividade das fibras cardíacas eferentes do vago (CVE) para durante a inspiração, causando “respiratory sinus arrythmia” (RSA)

Daly and Kirkman (1989) J. Physiol. 417, 323

Differential modulation of reflex cardioinhibitory responses by lung inflation in the cat

Lung inflation

cyanide pressure phenylbiguanide J-receptors

veratridine stimulation

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In mammals over 30% of VPN (vagal preganglionic neurones) and over 70% of cardiac VPN (CVPN) are located in the NA (nucleus ambiguus) with the rest in the dorsal motor nucleus (DVN)

Ranson, Butler and Taylor (1993) J. auton. Nerv. Syst. 43, 123- 138

DVN

NA

Jones, Wang and Jordan (1995) J. Physiol. 489, 203

Rat: compound cardiac action potentials

anodal block

B – fibres from NA C – fibres from DVN

Jones, Wang and Jordan (1995) J. Physiol. 489, 203

Rato Coelho Gato

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RSA is generated in the brainstem of mammals in an area called the nucleus ambiguus (NA). Activity in cardiac vagal preganglionic (motor) neurones (CVPN/CVM) that exercise a dominant role in control of the heart, is gated by activity in neighbouring inspiratory neurones

Mike Spyer and Dave Jordan (Spyer, 1989 TINS 12, 506-513)

RSA se desenvolve no tronco encefálico dos mamíferos, num local chamado nucleus ambiguus (NA).

Many physiologists and psychobiologists (because they work on mammals!) consider RSA to be a mammalian function (have the NA) not seen in “lower” vertebrates.

As Comparative Physiologists we recognise various forms of cardiorespiratory interactions (CRI) in a range of species

Muitos fisiologistas e psicobiólogos, por trabalharem com mamíferos, consideram RSA como uma função exclusiva desse grupo (tem NA) e ausente nos vertebrados “inferiores”.

Como estamos interessados em fisiologia comparativa, nós reconhecemos formas diferentes de interação cardiorespiratória (CRI) em muitas espécies

CHORDATE PHYLOGENY

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In the duck only 5% of VPN but 30% of CVPN are in the ventro-lateral NA

BIRDS:

Duck: cardiovascular and respiratory variables: effect of water on laryngeal receptors (Event)

Butler and Taylor, 1983 Respir. Physiol. 53, 109

REPTILES

often breath discontinuously, heart rate varies with ventilation

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REPTILES: Rattlesnake - Crotalus durissus terrificus

Complete vagotomy slows ventilation, increases heart rate and abolishes HRV

Wang, Warburton, Abe and Taylor (2001) Exp. Physiol. 86, 777

Estas mesmas respostas aparecem em mamíferos

Taylor et al. 2009

anaesthetised

Efferent electrical stimulation

Vagal  control  of  the  cardiac  shunt  

Pharmacological study of parasympathetic and sympathetic tone on the heart of the rattlesnake

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Rattlesnake = cascavel: diurnal changes in body temperature and heart rate (fH)

mudanças diárias na temperatura do corpo e na freqüência cardíaca

Rattlesnake: Power spectral analysis of heart rate variability shows evidence for RSA with peaks in the spectrum appearing, then shifting as heart rate (fH) slows during recovery from handling stress

Campbell, others and Taylor (2006) J. exp. Biol. 209, 2628

Rattlesnake: TS brainstem 0.5 mm caudal of obex

VPN labelled with true blue are in 2 locations: 96% in the DVN (núcleo motor dorsal) and 4% scattered ventrolaterally

Edge of brain

4V

Ventro-lateral cell

DVN

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A B

D2 V

D1

VL

D1

D2 V

Caiman - TS brainstem to show VPN labelled with True blue

Distribution of VPN in TS of brainstem

OTHER REPTILES – Brasil!!!

Boa constrictor

Caiman latirostris 12%

0 5

10 15 20 25 30

2.52 1.68 0.84 0 -0.84 -1.68 -2.52 Distance from obex (mm)

Group 2  Ventrolateral  

Group 1  

(nº c

ells

/ se

ctio

n) (n

º cel

ls /

sect

ion)

0 5

10 15 20 25 30

B

A rattlesnake

caiman

Taylor, Leite and Skovgaard (2010) Braz J Med Biol Sci.

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Uromastyx aegyptius microlepis

From Saudi Arabia

VPN were located in the DVN or DMNX and in the NA but only in small numbers (5%)

Mohammed Al-Ghamdi, 1995

Boa constrictor – cardiovascular responses to a meal or a bad time

Effects of autonomic blockade on heart rate during forced activity and digestion in Boa constrictor

Wang, Taylor, Andrade and Abe (2001) J Exp Biol. 204, 3553

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Heart of doubled-blocked animals increases during digestion

1.  Release of an excitatory NANC factor from cardiac nerve terminals ?

2.  Increased circulating levels of a NANC factor(s) ?

AMPHIBIANS: Toad/Bullfrog A

The vagus (X) provides: . afferent nerves to chemo and baroreceptors plus lung stretch receptors (PSR) (C) . efferent nerves to the lungs, glottis, heart plus a sphincter on the pulmonary artery (D)

Reflex control of respiratory and cardiovascular systems is similar to mammals

Wang, Hedrick, Ihmied and Taylor (1999) CBP

Respiratory muscles: inserted around the buccal cavity(A), innervated by cranial nerves V, VII and X plus XII (B)

B

C D

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Bufo: heart rate and pulmonary blood flow increase during bouts of breathing

Bullfrog: effects of autonomic antagonists on heart rate at 10, 20 and 30oC

Bullfrog: calculated autonomic tonus on the heart

Filled columns, cholinergic/vagal tonus

Open columns, adrenergic/sympathetic tonus

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Bullfrog, black columns

Xenopus, grey columns

V

Bullfrog 3 TS brainstem 0,12 mm rostral to obex Scale bar represents 100µm

V, 4th ventricle

V

Bullfrog 5 TS brainstem 0,34 mm rostral to obex Scale bar represents 100µm

V, 4th ventricle

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Bullfrog: Rostro-caudal distribution of cell bodies of VPN, with respect to obex

Distance  from  obex  (mm)  

no  cells  /  sec9o

n  

0

10

20

30

40

-2.7 -1.8 -0.9 0 0.9 1.8 2.7 3.6

Xenopus: Vagal projections into the brainstem located by axonal transport of HRP. There are 2 populations of VPN of differing in size and location, inside or outside central grey area.

TS medulla 1 mm rostral of obex

Rostro-caudal distribution of VPN in the medial DVN and in the lateral NA that innervate different organs.

About 30% of VPN are located outside the DVN

This is the same as mammals.

There is evidence of a residual sequential distribution.

Xenopus

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Axolotl, Ambystoma mexicanum

before and after induced metamorphosis

Axolotl: rostrocaudal distribution of VPN

Conclusions: All tetrapod vertebrates (amphibians, reptiles, birds and mammals) studied have neural mechanisms causing the heart to beat in relation to ventilation (CRI). This relationship is mediated via the vagus nerve.

2 locations for CVPN in the brainstem may be important for the generation of CRI but is not present in all species

Todos os vertebrados estudados possuem mecanismos neurais que fazem o coração bater de acordo com os ritmos ventilatórios (CRI). Essas relações são mediadas pelo vago.

CVPN em dois locais do tronco encefálico talvez explique a produção de CRI mas naõ tem de todos especies.

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PEIXE

Take five

Levar cinco

FISH: We have conducted a long-term study on the control of cardiorespiratory interactions in fish. Sometimes they show cardiorespiratory synchony (CRS), with the heart beating in phase with ventilation.

This may increase the effectiveness of respiratory gas exchange across the counter-current between blood on water at the gills

Há vários anos, estamos estudando o controle da interação cardiorespiratória em peixes. Algumas vezes, os resultados mostram sincronia cardiorespiratória (CRS), com o coração pulsando em fase com a ventilação.

Isso pode aumentar a eficiência da troca respiratória de gases, nas brânquias, entre o sangue e a água

Counter-current exchange of O2 over fish gills

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Counter-current exchange of O2 over fish gills

Elasmobranch Dogfish: Ventilation (VR) and heart (HR) rates recorded as pressures A. From resting dogfish (normal) and following injection of atropine and B. during a spontaneous period of activity

Teleost Cod: Blood pressure and flow in the dorsal aorta plus water pressure in the buccal cavity

Cardiorespiratory synchrony:

Cod: polar diagrams of heart beat related to respiratory cycle

normoxia hypoxia

Jensen, Varne, Findorf, Dominici, McKenzie, Wang and Steffensen unpublished

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When trout ram ventilate heart rate rises. This may indicate loss of a respiration related vagal component

Jones, Wang and Jordan (1995) J. Physiol. 489, 203

How can fish generate beat-to-beat changes in heart rate?

In mammals:

C – fibres conduct at around 2 metres / second (DVN)

B – fibres conduct at around 20 metres / second (NA)

Dogfish cardiac vagus compound action potential- conduction velocity 7-35 metres/second

Barrett and Taylor (1985) J. exp. Biol. 117, 459

3 cm of nerve

5 volts

25 volts

10 volts

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They are the first group to possess an autonomic nervous system BUT – the sympathetic nervous system does not extend into the “head”

consequently the heart only has parasympathetic vagal innervation

Thus, the dogfish brainstem provides a model for vagal control of cardiorespiratory interactions

Eles são os primeiros (Chondricthyes) com sistema nervoso autônomo, MAS – o sistema nervoso simpático não atinge a “cabeça” e, conseqüentemente, o coração somente possui inervação parassimpática

Dessa forma, o tronco encefálico do dogfish representa um modelo para estudar o controle do vago na interação cardiorespiratória

The Chondrichthyes (cartilaginous, elasmobranch fish) are phylogenetically a “primitive” group (>300M years)

Innervation of the heart:

Elasmobranchs Chondrichthyes (cartilaginous fish)

solely parasympathetic supply

Teleosts Osteichthyes (bony fish)

parasympathetic and dual sympathetic supply

as “advanced” as mammals!

heart

brain

brain

heart

vagus

Sympathetic ganglia

Dogfish: Schematic diagram of branches of cranial nerves V, VII, IX and X, innervating the respiratory system and heart

X br c branchial cardiac X visc c visceral cardiac

A neural tracer (HRP) was injected into branches of cranial nerves V, VII, IX and X

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cobalt chloride

Horseradish peroxidase True

blue

Dogfish: Sequential rostrocaudal distribution of neurones supplying the respiratory and cardiac branches of the cranial nerves

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Dogfish: spontaneous activity in central cut branches of the cranial nerves supplying respiratory muscles and the heart

Atividade espontânea dos nervos cranianos controlam os músculos respiratórios e o coração

Dogfish: decerebrate and paralysed Efferent activity in cardiac and branchial vagi

(non-bursting activity seems responsible for reflex control of heart rate and generation of vagal tone, which increases during hypoxia)

There are 2 types of efferent activity recorded from the cardiac vagus of the dogfish.

Neuranatomical study revealed 2 locations for CVPN in the brainstem: a medial group in the dorsal vagal motor nucleus and a scattered ventro-lateral group outside the DVN

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Dogfish: Schematic dorsal view and TS of hindbrain, shaded areas denote motor nuclei to V, VII, IX and Xth cranial nerves

Having located neurone cell bodies in the brainstem we recorded from them using microelectrodes

Dogfish: central recordings of activity in CVPN

Cells located in the DVN showed respiration-related activity (A) Those outside the DVN were routinely active (B) or silent (C)

Activity in all CVPN could be generated by touching gill septa (stim)

Fish were paralysed and decerebrated, removing any phasic influences from peripheral receptors or centres higher in the CNS

RF reticular formation; Xs vagal sensory nucleus; Xm, vagal motor nuclei; X4 4th branch of vagus nerve occ. sn. occipital and spinal nuclei; hypobranchial

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Respiration-related, phasic activity was recorded from CVPN in the DVN of paralysed and decerebrated fish implying that it was generated by feed-forward control from the central respiratory pattern generator

Mechanical stimulation of a gill septum caused CVPN to fire, implying that in the normally breathing fish mechanoreceptor stimulation would induce reflex activation of CVPN

The effects on heart rate of phasic activity in the cardiac vagus was tested by peripheral stimulation

Dogfish: Peripheral electrical stimulation of a cardiac nerve A, with a continuous train of impulses B, with continuous and phasic trains of pulses

Dogfish: Recruitment of heart rate to phasic peripheral stimulation of the right cardiac branch of the vagus

Taylor et al (2006) PBZ

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Putative conclusions: Elasmobranch fishes have no excitatory sympathetic innervation of the heart

They do have a parasympathetic inhibitory supply to the heart

It arises from CVPN in 2 locations in the brainstem:

A medial group in the dorsal vagal motor nucleus DVN show respiration related activity and may generate CRI

A lateral group do not and may generate phasic changes in heart rate (e.g. hypoxic bradycardia)

Both groups of CVPN respond to mechanical stimulation so will be recruited by ventilation

Bursting efferent activity in the cardiac vagus can drive the heart, over-riding the cardiac pacemaker

2006 - Tadeu Rantin’s laboratory UFSCar Sao Carlos, SP. Brasil

A teleost model: Pacu – Piaractus mesopotamicus

Pacu is unique?

A.  Does not respond to hypoxia or injection of nicotine with a significant increase in circulating catecholamines (adrenaline/epinephrin) implying inoperative or absent humoral adrenergic response

B.  Injection of propranolol (beta-adrenergic antagonist) after atropine injection revealed that the excitatory adrenergic tone on the heart in pacu is below 10%.

C.  Thus, the predominant factor controlling heart rate in pacu is inhibitory parasympathetic control, imposed via the vagus nerve, innervating muscarinic cholinoceptors.

A. Não responde à hipoxia ou injeção de nicotina com um significante aumento na circulação das catecolaminas (adrenalina/epinefrina) - resposta humoral adrenérgica inoperante ou ausente B. Injeção de propanolol depois de injeção de atropina – estímulo adrenérgico no coração do pacu é menor que 10%. C. Sendo assim, o principal fator que controla o ritmo cardíaco, em pacu, é o controle parassimpático inibidor, determinado pelo nervo vago nos receptores muscarínicos

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A

B

* * * *

* *

Pacu - Recordings from the cardiac vagus, ventilation and ECG

•  No routinely respiration-related bursts in cardiac vagus in normoxic fish

* increased ventilatory effort ** cough

Pacu - Effect of stopping the water flow irrigating the gills

•  Increased activity in cardiac vagus is associated with increased ventilatory effort and generates a bradycardia

Pacu - Restricting water flow

•  Increased ventilation amplitude generated bursting activity in the cardiac vagus that recruited the heart

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SO:

The heart can be recruited by bursting activity in the cardiac vagus, generated by reducing the supply of oxygen.

Can this effect be simulated by peripheral electrical stimulation of the cardiac vagus?

O ritmo cardíaco corresponde à atividade fásica do vago cardíaco, fenômeno causado pela redução do nível de oxigênio.

Pode esse efeito ser simulado por estimulação elétrica periférica no vago cardíaco?

Pacu - Pulsed efferent stimulation of the cardiac vagus can drive the heart both slower or faster than its intrinsic rate

If bursting activity recorded from the cardiac vagus is dependent on phasic peripheral feedback from receptors in the branchial apparatus when oxygen supply is limited (most likely to be mechanoreceptors on the gill arches, opercula or jaws),

Then, can phasic central stimulation of cranial nerves innervating the respiratory apparatus recruit the heart?

Se a atividade fásica do nervo vago cardíaco depende do feedback fásico emitido pelos receptores do aparelho branquial quando o suprimento de oxigênio é limitado,

Então, poderia a estimulação fásica e central dos nervos cranianos, que inervam o aparelho respiratório, fazer o coração bater sincronicamente com os estímulos?

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Pacu – effects on heart rate of central stimulation of cranial nerves IX, X, VII, and V to respiratory muscles

**

Phasic stimulation of VII, IX and X recruited the heart but V was without effect **

Pacu

G1 dorsal DVN (40%)

G2 ventral DVN (60%)

LC lateral CVPN (2%)

V 4th ventricle CVPN

RVMN

Cardiac vagal preganglionic neurones (CVPN) and respiratory vagal motor neurones (RVMN) located in the dorsal vagal motor nucleus (DVN) in the brainstem by fluorescent tracers.

There seems to be abundant evidence for the supremacy of feedback from peripheral receptors on the gills or opercula (but not the jaws!) in the generation of cardiorespiratory interactions (CRI) in pacu, a teleost fish.

VPN are predominantly located in DVN

But, is this the complete answer?

Existem muitas evidências sobre o papel do feedback dos receptores periféricos, das brânquias ou opérculos (mas não da mandíbula), em promover uma interação cardiorespiratória (CRI) em pacus.

Mas, essa pergunta está completa?

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Rostro-caudal distribution of RVMN and CVPN in the brainstem. Respiratory neurones innervating the Vth cranial nerve do not overlap with other neurones

**

Pacu -

Pacu

Recordings of ventilation as opercular movements and integrated activity in cranial nerves V, IX, X 1st and 2nd branchial and 4th cardiac

sequence of bursting activity in cranial nerves.

Bursts in cardiac nerve are synchronous with activity in Vth cranial nerve, innervating the jaw.

Both anticipate activity in other respiratory branches.

Pacu –

A atividade fásica dos nervos cardiacos é sincrônica com a atividade do 5º nervo craniano, que inerva a mandíbula (d)

Ambos antecipam a atividade em outros ramos respiratórios (e)

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SO:

•  There is evidence of an important role for peripheral feedback in generating CRI in pacu.

•  There remains a possibility that central, feed-forward drive from a central respiratory pattern generator can drive both the respiratory neurones innervating the jaw and CVPN innervating the heart, when respiratory drive is high.

•  This may determine the phase relationships between heart beat and ventilation, optimising oxygen delivery across the gills.

•  Existem evidências de que o feedback periférico promove CRI em pacus •  Sobra a possibilidade do feed-forward do controle central gerar CRI, por inervar tanto neurônios respiratórios como o CVPN. •  Isso pode determinar a relação sincrônica entre o batimento cardíaco e a ventilação, otimizando a captura do oxigênio nas brânquias

In elasmobranchs CRS seems to be primarily determined by central, feed-forward control when vagal tone on the heart is low (Taylor, 1992)

In teleosts control seems to depend on feedback from peripheral receptors generating high levels of cardiac vagal tone (Randall and Smith, 1967)

Nos elasmobrânquios, CRS parece ser determinada por um controle central, feed-forward, quando o tonus vagal no coração é baixo (Taylor, 1992)

Nos teleósteos, o controle parece depender do feedback dos receptores periféricos gerando altos níveis de tonus vagal cardíaco (Randall and Smith, 1967)

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CPG, central pattern generator; CVM, cardiac vagal motor neurone CVS, cardiac sensory RVM, respiratory motor; RVS, respiratory sensory

We have some limited insights into 1 - 8 but cannot yet completely delimit their roles

A schematic model of possible connections in the central and peripheral nervous systems generating cardiorespiratory interactions in fish

RF reticular formation; Xs vagal sensory nucleus; Xm, vagal motor nuclei; X4 4th branch of vagus nerve occ. sn. occipital and spinal nuclei; hypobranchial

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Evolution of the NA: There is a progressive increase in the proportion of VPN in the ventro-lateral NA, from fish through amphibians to mammals but reptiles are complicated and birds out of line.

However, 2 populations of CVPN may be needed to generate CRI

Grossman and Taylor (2007) Biol. Psychol. 74, 26