Central control of cardiovascular system- sympathetic side

Question 1

Where are the SPNs of sympathetic division of ANS located?

Answer 1

thoraco-lumbar region = T1-L2
SPNs for the eye and salivary gland are within upper regions
SPNs for bladder and ovary are located within lower regions

Question 2

Where are SPNs located in the spinal cord?

Answer 2

lateral horn/ intermediolateral cell column - majority here

Question 3

What pathway and neurotransmitter do SPNs use?

Answer 3

cell bodies within IML and then axons leave via ventral root to synapse onto postganglionic neurones which then invert the end organ
SPNs release ACh onto postganglionic neutrons

Question 4

What is the only gland that is activated directly by the preganglionic sympathetic neurone?

Answer 4

adrenal gland

Question 5

What effects upon the heart is sympathetic output important for ?

Answer 5

important for force of contraction and also heart rate

Question 6

Why is sympathetic outflow to blood vessels important ?

Answer 6

it is useful to increase blood flow to the muscles and reduce its flow to the skin

Question 7

What is transneuronal tracing ?

Answer 7

it involves using a viral tracer that can cross synapses
useful for determining circuits
neurones are infected with the viral tracer and for retrograde tracers, it will travel back upon the neutron and then cross synapses to infect the previous neurones within the circuit
e.g virus injected into end organ then it goes to the postganglionic neurone, then preganglionic neurones and then onto CNS

Question 8

How have the different spinal regions been shown to have different function ?

Answer 8

using transneuronal labelling
after tracer has been injected and left to travel through the circuit, slices can be taken to determine which neurones are labelled and therefore their regions can also be determined.

Question 9

What has the labelling of spinal regions demonstrated?

Answer 9

same regions within the spinal cord innervate different organs, therefore you cant remove specific organs for a particular organ. there is overlap between them

Question 10

What happened to the heart when they excited the right hand SPNs ?

Answer 10

it caused a greater change in heart rate, therefore these neurones are thought to have greater chronotropic effects

Question 11

What happened to the heart when they excited the left hand SPNs?

Answer 11

there was a greater change in left ventricular pressure, therefore these neurones are thought to have greater ionotropic effects

Question 12

What happened when they injected small amounts of glutamate into different levels of the spinal?

Answer 12

it demonstrated that T2 and T3 produced the greatest effects and therefore most of the neurones innervating the heart must be located here

Question 13

How did they demonstrate that interneurones project to SPNs?

Answer 13

used 2 tracers, one which crosses synapses and one that cant
injected tracers into sympathetic ganglion which retrogradely travelled back up into SPNs cell body, the tracer which crossed the synapse labelled many interneurones

Question 14

What have they shown about the interneurones that synapse onto SPNs?

Answer 14

they were GABAergic
colocalised expression of the tracer and labelled for GAD-67
if these interneurones are GABAergic, then they are inhibitory and can therefore slow down the sympathetic outputs

Question 15

What happens to descending control of sympathetic outflow after spinal cord injury ?

Answer 15

massive decline in neuronal activity coupled with low BP and autonomic dysreflexia- lose bladder and bowel control and sexual function
depending on the level of the injury they can suffer completely inappropriate responses, such as inappropriate cardiovascular responses

Question 16

What has transneuronal labelling shown about the supra spinal regions involved in autonomic activity ?

Answer 16

that the RVLM is important in control of the cardiovascular system, many neurones labelled there after SPN retrograde transneuronal tracer was injected

Question 17

What other supra spinal regions project to the SPNs?

Answer 17

biggest inputs from C1 adrenergic neurones in RVLM, serotonergic neurones in raphe complex, A5 noradrenergic neurones as well as projections from the pons and medulla
there are also projections from the paraventricular nucleus and lateral hypothalamic area

Question 18

What happens if you ablate the RVLM?

Answer 18

blood pressure shoots right down, demonstrating its important in control of BP

Question 19

What happens when glutamate is injected into the RVLM?

Answer 19

BP and HR increase and lumbar and renal sympathetic outputs also increase

Question 20

How was optogenetic stimulation carried out in the RVLM?

Answer 20

inserted optogenetically activated channels into c1 neurones within the RVLM, to determine the c1 neurones they used the fluorescent marker mCherry to label the neurones expressing TH
when they shone the light upon these cells there was an increase in BP and HR and sympathetic nerve discharge
showing the importance of the neurones in sympathetic output

Question 21

What descending inputs are there onto SPNs?

Answer 21

both descending excitatory and inhibitory inputs from medulla onto SPNs

• EPSPs= activates excitatory amino acids receptors
• IPSPs= activates GABAergic receptors- interneurones

Question 22

Where do baroreceptors project into ?

Answer 22

project into NTS which then projects to the CVLM
the CVLM provides an inhibitory effect onto the RVLM to restore normal BP levels - prevents the RVLM releasing excitatory inputs onto SPNs to enhance BP

Question 23

What happens if glutamate anatagonists are injected into the NTS?

Answer 23

they block the baroreceptor inputs- inhibiting the reflex inhibition
this all indicates that the NTS is important in this pathway

Question 24

What effect to GABA antagonists in the RVLM cause?

Answer 24

also blocks baroreceptor reflex

blocks the inhibitory effect from the CVLM

Question 25

Why was c-fos expression used in determining regions involved in baroreceptor reflex and how ?

Answer 25

decrease BP and then allow it to be restored.
looked for the active neurones during restoration of BP by looking for the expression of c-fos in neurones
demonstrated that the RVLM and A5 region of the pons is labelled and therefore it is important

Question 26

How is the raphe nucleus involved in cardiovascular control ?

Answer 26

when it is activated, HR and BP increase
think it is important in stress induced increase in their parameters
think the raphe nucleus is activated by the hypothalamus

Question 27

How does the renin-angiotensin system contribute to blood pressure changes ?

Answer 27

decreased renal perfusion leads to renin release
renin converts angiotensinogen to angiotensin 1
angiotensin converting enzyme converts angiotensin 1 to angiotensin2
angiotensin2 increases sympathetic activity, increasing BP, acts at the suprarenal gland and hypothalamus and RVLM

Question 28

Which level of the spinal cord are SPNs for atrial myocardium located?

Answer 28

t1-t6

Question 29

Which level of the spinal cord are SPNs for ventricular myocardium located?

Answer 29

t1-t7