Autonomic Cardiac Control Seminar

Question 1

Which branch of the autonomic nervous system is dominant in humans at rest?

Answer 1

Parasympathetic nervous system

Question 2

Give a likely mechanism of action of sympathovagal interactions.

Answer 2

The release of acetylcholine from parasympathetic neurons might act presynaptically to inhibit the release of norepinephrine from sympathetic nerve terminals

The parasympathetic-sympathetic interaction might also be the result of competition postsynaptically between different guanine nucleotide-binding (G) proteins within the membranes of sinoatrial pacemaker cells

Question 3

Give examples of conditions where you are likely to see a reduced level of cardiac vagal activity.

Answer 3

Hypertension

Heart failure

Question 4

What is meant by the term ‘antidromically’?

Answer 4

An antidromic impulse in an axon refers to conduction opposite of the normal direction, along the axon away from the axon terminal(s) and towards the soma.

Question 5

Where in the brainstem would you find the cell bodies (soma) of preganglionic cardiac vagal neurones?

Answer 5

The nucleus ambiguus

Question 6

Which 3 currents are responsible for the firing characteristics of cardiac vagal neurones?

Answer 6

Transient K+ current
TEA-sensitive delayed rectified K+ channel
Ca2+ -activated K channel

Question 7

Are cardiac vagal neurones tonically active in vitro?

Answer 7

No

Question 8

In vivo what do cardiac vagal neurones depend upon to fire?

Answer 8

The firing of cardiac vagal neurons is totally dependent on critical synaptic input to these neurons

Question 9

What type of pathway links the nucleus tractus solitarii (NTS) and the nucleus ambiguus (NA)?

Answer 9

A glutamatergic pathway

Question 10

What experiments have been done to show the presence of a glutamatergic pathway between the NTS and the NA?

Answer 10

Electrophysiological experiments, in which the NTS region is stimulated and postsynaptic responses are
recorded in either unidentified ambiguus neurons or identified vagal cardiac neurons

Question 11

What is the physiological outcome following activation of the glutamatergic pathway between the NTS and NA?

Answer 11

Activation of a postsynaptic excitatory amino acid receptors including a long lasting NMDA-mediated
current and a rapidly activating and inactivating non-NMDA receptor response.

Question 12

Define respiratory sinus arrhythmia.

Answer 12

In each respiratory cycle the heart beats more rapidly in inspiration and slows during postinspiration and expiration

Question 13

What is the main cause of respiratory sinus arrhythmia?

Answer 13

The dominant source of respiratory sinus arrhythmia originates from the brain stem

Question 14

Where does the cardiorespiratory interaction occur?

Answer 14

Within the nucleus ambiguus

Question 15

Which neurotransmitters in the central nervous system are likely to be involved in respiratory sinus arrhythmia?

Answer 15

Acetylcholine

Question 16

What are the proposed mechanisms of action concerning the activation of cardiac vagal neurones by cholinergic neurones during the post-inspiratory phase?

Answer 16

Cholinergic neurons active in postinspiration could influence cardiac vagal neurons via three independent mechanisms:
1. a direct activation of postsynaptic ligandgated
nicotinic channels in cardiac vagal neurons
2. presynaptic activation would evoke a nicotinic facilitation of presynaptic release of glutamate
3. activation of nicotinic receptors that facilitate postsynaptic non-NMDA receptors in cardiac vagal neurons

Question 17

Where are the Cardiac vagal neurons primarily located?

Answer 17

Nucleus ambiguus (NA)
Dorsal motor nucleus of the vagus (DMV)

Question 18

Give examples of the excitatory inputs to the cardiac vagal neurons

Answer 18

Glutamatergic pathway from the NTS

Cholinergic nicotinic receptors that can excite cardiac vagal neurons at both presynaptic and postsynaptic site

Question 19

How does microinjection of bicuculine (GABA antagonist) into the NA affect heart rate?

Answer 19

Decreases heart rate

Question 20

Why does microinjection of bicuculine into the NA decrease heart rate?

Answer 20

By blocking a tonically active GABAergic input to cardioinhibitory cardiac vagal neurons

Question 21

What type of input do the cardiac vagal neurons receive from the NTS?

Answer 21

Monosynaptic GABAergic input

Question 22

Where do the preganglionic vagal neurons synapse?

Answer 22

With the post-ganglionic cardiac vagal neurons located at the base of the heart

Question 23

During the experiment by Mendelowitz (2001), how old were the rats used?

Answer 23

6-12 days

Question 24

During the experiment by Mendelowitz (2001), what happened to the rats during surgery?

Answer 24

The rats were anaesthetised and exposed to hypothermia (10-20mins).

A thoracotomy was performed, and a fluorescent dye was injected into the pericardial sac

Question 25

During the experiment by Mendelowitz (2001), how were the rats anaesthetised?

Answer 25

Inhaled methoxyflurane

Question 26

During the experiment by Mendelowitz (2001), why were the rats exposed to hypothermia?

Answer 26

To slow the heart and aid in recovery

Question 27

During the experiment by Mendelowitz (2001), what dye was injected into the pericardial sac?

Answer 27

Rhodamine

Question 28

During the experiment by Mendelowitz (2001), when were the rats killed?

Answer 28

3-7 days after the initial surgery

Question 29

During the experiment by Mendelowitz (2001), how were the rats killed?

Answer 29

They were anaesthetised and killed by rapid cervical dislocation

Question 30

During the experiment by Mendelowitz (2001), what part of the rat brain was removed?

Answer 30

The hindbrain

Question 31

During the experiment by Mendelowitz (2001), where was the hindbrain placed after removal?

Answer 31

Placed for 1 min in cold (0–2C) buffer, and continually

gassed with 100% O2

Question 32

During the experiment by Mendelowitz (2001), what did the buffer the hindbrain was placed in contain?

Answer 32

NaCl (140 mM)
KCl (5 mM)
CaCl2 (2mM)
Glucose (5 mM)
HEPES (10 mM)

Question 33

During the experiment by Mendelowitz (2001), the rat hindbrain was sliced with a Vibratome. How thick were the slices?

Answer 33

250-350 micrometres