CNS control of body temperature

Question 1

What 3 main responses occur when we are cold ?

Answer 1

1) our muscles shiver to generate heat
2) blood vessels constrict blood away from the extremities to reduce heat loss - vasoconstriction
3) BAT- heat energy produced from oxidation of FFA

Question 2

Why are thermoreceptors so essential to temperature regulation and where do they project into ?

Answer 2

within the skin they are able to respond to temperature changes very quickly - very sensitive
project into dorsal of spinal cord and then from the neurones are projected up to the central processing

Question 3

What happens in raynaud’s syndrome?

Answer 3

the blood vessels to the extremities constrict too much

Question 4

Why is it beneficial for rabbits to have huge ears ?

Answer 4

they are good at losing heat

- many animals have specific mechanisms to control temperature

Question 5

How does the sympathetic nervous system act to influence the activity in the BAT?

Answer 5

it increases lipase activity which increases the production of FFA available for oxidation
increases the amount of uncoupling protein in the mitochondria by increasing transcript- to enhance thermogenic response

Question 6

Why is uncoupling protein important and where is it found?

Answer 6

uncoupling protein 1 is present within the mitochondria and it is important in combustion of FFA to produce heat

Question 7

What is broken down to FFA ?

Answer 7

Triglycerides are broken down within BAT to produce FFA

Question 8

What experiment in humans was carried out into BAT activity ?

Answer 8

took a lot of men and put them in a 19 degrees environment and then placed their feet on ice blocks and then given 18-deoxyfluroglucose- which is an active marker of high energy use to observe the areas of high activity
when they looked at the amount of BAT there were many more darker stained areas compared to humans at normal temperature indicating that there was higher levels of BAT activity in the colder temperatures

Question 9

Do neonate rats have high or low levels of BAT after birth and why ?

Answer 9

low levels that develop gradually after birth
rats tend to huddle together after birth and therefore this is why they have low BAT - the levels increase once they become more independent but if you removed a baby rat from its litter then it will struggle to survive because it doesn’t have sufficient BAT to survive
also in thermoneurtral conditions, their levels of BAT remain low

Question 10

Do neonate baby kangaroos have high or low levels of BAT after birth and why ?

Answer 10

they have very low BAT at birth and it takes them a lot longer to develop it which is why they are placed in their mothers pouch- very dependent upon their mothers warmth
if they were removed from their mother after birth they would seriously struggle to survive
in thermoneutral condition BAT recruitment remains low

Question 11

Do neonate lambs have high or low levels of BAT and why ?

Answer 11

they have high levels because they need it to enable them to survive in a field
not as dependent on their mothers for warmth
in normothermic conditions their levels start high and then reduce

Question 12

What did injecting PRV into BAT do ?

Answer 12

demonstrated that postganglionic neurones were present in the stellate ganglion and the preganglionic sympathetic neurones are in the thoracic region of the spinal cord (T3-T6)

Question 13

What did they see when they recorded from dorsal horn neurones?

Answer 13

they recorded greater frequency of action potentials when the skins surface temperature was reduced but when the temperature was increased the firing was reduced
detecting non-noxious temperatures

Question 14

What are the %’s of warm-sensitive and cold sensitive neurones in laminae 1/2 ?

Answer 14

warm = 53%
cold= 2%
there are a lot more warm sensitive than cold sensitive in the DH

Question 15

What are the %’s of warm-sensitive and cold-sensitve neurones in the pre-optic are of hypothalamus?

Answer 15

warm= 46%
cold= 5%

Question 16

What structure does the DH project to and how did they determine this ?

Answer 16

Lateral parabrachial nucleus
they knew that the DH projected to the hypothalamus but they didn’t know what area was involved before it reached the hypothalamus
injected fluorogold which is a retrograde tracer into the hypothalamus, this tracer labelled neurones in the lateral parabrachial nucleus
injected PHA-L, an anterograde tracer into the DH which then went on to label the parabrachial nucleus
- this dual tracing techniques proved the lateral parabrachial nucleus was the intermediate structure involved

Question 17

What did they do to further prove the lateral parabrachial nucleus was involved ?

Answer 17

they inhibited the LPB and this stopped the cold response
- hyper polarised with muscimol (GABA agonist)
also recorded from single lateral parabrachial neurones and then reduced the skins temp and they saw that they were active. Their activity was maintained during the cold and it correlated with recordings to the BAT- increased sympathetic activity to the tissue

Question 18

How is the raphe nuclei involved ?

Answer 18

it is part of the descending arm of the pathway
it is the only place where 5HT is produced
injected PRV into the BAT to look at the relay and they saw once its gone back to the stellate ganglion it then goes to the spinal cord and then onto the raphe nucleus
the serotonergic neurones in the raphe nuclei provide excitatory inputs onto sympathetic neurones

Question 19

What happened when NMDA was applied to the raphe pallidus?

Answer 19

excitatory amino acid increased the activity within the raphe pallidus and this led to increased BAT activity, increased sympathetic activity and increases in temperature and HR

Question 20

What other experiments further proved that the raphe pallidus is important for excitatory inputs in the cold response?

Answer 20

microinjected 5HT into the SC where the SPNs are present and this induces the same effect as activating the raphe pallidus
also inhibited the raphe nuclei and this abolished BAT activity highlighting that its activity is necessary for the pathway

Question 21

What is another function that raphe nuclei activity is important for ?

Answer 21

important for controlling blood vessels- controlling the levels of dilation and constriction
- different brain regions control blood vessels which are critical for heat loss/retention

Question 22

In the cold response pathway why is the DMH important?

Answer 22

important in the descending arm

it projects to the raphe pallidus to induce excitation

Question 23

What happens between the median pre optic nucleus and the DMH?

Answer 23

normally the medial pre optic (MPO) releases GABA onto the DMH to inhibit thermogenesis however during the cold response this effect is disinhibited by the median pre optic area MnPO releasing GABA onto the MPO to inhibit the warm sensitive neurones to prevent inhibition of the DMH

Question 24

Why is the activity of the medial pre optic nucleus so important?

Answer 24

its inhibition onto the DMH provides a break in the system- if this didn’t happen then we would continually get hotter and hotter as thermogenesis wouldn’t be inhibited

Question 25

What is mainly present in the MPO?

Answer 25

seems to mainly contain warm-sensitive neurones - as they respond to warm temperature signals then they are able to induce the break on thermogenesis once temperature is back to normal

Question 26

Under normal conditions what is happening to the DMH?

Answer 26

it is under inhibitory control

Question 27

What happens when the inhibitory control of DMH is inhibited by bicuculline?

Answer 27

massive increase in temperature and heart rate

increase in core and BAT temperature

Question 28

What happens to thermogenic responses to stress if the DMH is inhibited?

Answer 28

thermogenenic responses to social stress are reduced

stress releases the break on the DMH

Question 29

What happened when intruder wisteria rats were placed into a cage of long evans rats?

Answer 29

it induces a social stress response
causing an increased BAT temp and increased core temp
but if the DMH is switched off by muscimol then the increased temp is inhibited

Question 30

Other than stress what can release the break on the DMH?

Answer 30

fever can release the break and cause thermogenesis

Question 31

What happens when PGE2 is injected into the medial pre optic area?

Answer 31

increased BAT temp and core temp

Question 32

What is a condition with abnormal temperature regulation ?

Answer 32

narcolepsy

• disrupted sleep
• obesity
• loss of temp regulation- due to loss of orexinergic activity to BAT
• loss of orexin neurones - loss of input to raphe pallidus