CNS control of body temperature Flashcards
What 3 main responses occur when we are cold ?
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
Why are thermoreceptors so essential to temperature regulation and where do they project into ?
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
What happens in raynaud’s syndrome?
the blood vessels to the extremities constrict too much
Why is it beneficial for rabbits to have huge ears ?
they are good at losing heat
- many animals have specific mechanisms to control temperature
How does the sympathetic nervous system act to influence the activity in the BAT?
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
Why is uncoupling protein important and where is it found?
uncoupling protein 1 is present within the mitochondria and it is important in combustion of FFA to produce heat
What is broken down to FFA ?
Triglycerides are broken down within BAT to produce FFA
What experiment in humans was carried out into BAT activity ?
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
Do neonate rats have high or low levels of BAT after birth and why ?
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
Do neonate baby kangaroos have high or low levels of BAT after birth and why ?
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
Do neonate lambs have high or low levels of BAT and why ?
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
What did injecting PRV into BAT do ?
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)
What did they see when they recorded from dorsal horn neurones?
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
What are the %’s of warm-sensitive and cold sensitive neurones in laminae 1/2 ?
warm = 53%
cold= 2%
there are a lot more warm sensitive than cold sensitive in the DH
What are the %’s of warm-sensitive and cold-sensitve neurones in the pre-optic are of hypothalamus?
warm= 46% cold= 5%
What structure does the DH project to and how did they determine this ?
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
What did they do to further prove the lateral parabrachial nucleus was involved ?
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
How is the raphe nuclei involved ?
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
What happened when NMDA was applied to the raphe pallidus?
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
What other experiments further proved that the raphe pallidus is important for excitatory inputs in the cold response?
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
What is another function that raphe nuclei activity is important for ?
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
In the cold response pathway why is the DMH important?
important in the descending arm
it projects to the raphe pallidus to induce excitation
What happens between the median pre optic nucleus and the DMH?
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
Why is the activity of the medial pre optic nucleus so important?
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
What is mainly present in the MPO?
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
Under normal conditions what is happening to the DMH?
it is under inhibitory control
What happens when the inhibitory control of DMH is inhibited by bicuculline?
massive increase in temperature and heart rate
increase in core and BAT temperature
What happens to thermogenic responses to stress if the DMH is inhibited?
thermogenenic responses to social stress are reduced
stress releases the break on the DMH
What happened when intruder wisteria rats were placed into a cage of long evans rats?
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
Other than stress what can release the break on the DMH?
fever can release the break and cause thermogenesis
What happens when PGE2 is injected into the medial pre optic area?
increased BAT temp and core temp
What is a condition with abnormal temperature regulation ?
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
