Heat and Cold Bites: Frostbite, Fish that make cold feel hot and hot feel cold, warm + cold = hot
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Has anyone else noticed how crazy the weather has been
lately? Well it got me thinking about the quirky ways our body reacts to
temperature: and really the more you consider it, the crazier it all seems! From fish that makes you think hot is cold and cold is
hot (yes really!) to “cold burns”, there are so many weird and wonderful ways our body reacts to temperature extremes, and so many questions to answer. For example, why does peppermint make your mouth
go cold? Or why does incredibly hot water sometimes feel cold? Below I have tried to
share some of my
research into these little mysteries, and added a few more questions of my own.
Feeling the burn: Frostbite and what exactly happens with
“cold burn”?
After
burning my finger making ice cream, I was particularly interested in what was happening to my skin on a biological level. Was it the formation of ice crystals that was causing the damage? Or was it something else?
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After a bit of investigation I found a wonderful resource by Giesbrecht, who names two key things that happen in "cold burn".
1.
Dehydration: the wrath of the ice crystals
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When
tissue becomes cold, ice crystals form between cells and take their water away
causing dehydration, This is because
the crystals around the cells are more concentrated than the water in the cell
(i.e. they have a higher osmotic pressure), forcing water out of the cell, and
in the process damaging the cell.
2.
“Cold”
Arteriosclerosis” and damage to blood vessels
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One
of the body’s responses to the cold is to constrict the blood vessels. This
means that blood flow through smaller vessels is often disrupted in “cold burn”.
With impaired blood flow to tissues, oxygen is not delivered to the tissue
causing cell injury. But this only gets worse…. because in cold burn, the cells
lining the capillaries (the endothelial cells) leak as well. This is dangerous
for a number of reasons, but partly because it reduces blood volume which means
that blood cells carrying oxygen may stop moving altogether forming blood
clots, and further obstructing the blood vessels. In fact the effects of frostbite have been compared to arteriosclerosis.
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(https://books.google.co.uk/books?id=ayeercQ9DEwC&pg=PA76&lpg=PA76&dq=frostbite+mechanism&source=bl&ots=7xn05LjMSf&sig=Ys5eFxptqqq1ir3y4tjyzo4Cvo4&hl=en&sa=X&ved=0ahUKEwiOrMnxtf_UAhWJYVAKHeENDGAQ6AEIeTAQ#v=onepage&q=frostbite%20mechanism&f=false)
When Hot is Cold and Cold if Hot: “Paradoxical cold”
Imagine you are getting into the bath and you want to make
sure the water isn’t too hot. So you put a finger in, just to check, and the
water feels cold - all set. Prepared for a nice cooling bath, you get in, and
then you are suddenly confronted with scorching hot water. So what happened? Is
your body broken?
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In short: no. What you just experienced is a phenomenon is
known as “paradoxical cold” :a term coined by Max von Frey in 1895. In
paradoxical coldness, extreme heat is registered by the body as coldness. Interestingly,
you are more likely to experience the paradoxical cold phenomenon the warmer
your body temperature is because your
“cold threshold” is lowered. It also works the other way, with paradoxical
heat”: when something is so cold it feels hot.
Whilst the exact reason behind paradoxical heat and coldness
is so far unknown, there are two key theories:
Hot and cold receptors on the same neurones: this is the idea
that extreme temperature signals can be misinterpreted, so the brain senses
extreme heat as coldness. This could be because the receptors for heat (TRPV1)
and cold (TRPM8) can be found on the same sensory nerves (https://link.springer.com/referenceworkentry/10.1007%2F978-3-540-29805-2_3184)
Neurones “doubling up” : This is the idea that cold receptors
have a dual role, to both sense cold temperatures AND to help the brain detect
harmful temperature extremes. In one recent study, it was shown that similar
brain regions are activated with extreme heat and extreme cold (https://www.physicsforums.com/threads/hot-can-be-cold-and-cold-can-be-hot-what.374522/)
Crazy chemicals: chillis, gum and….fish?
- Cold peppermint? Have you ever
noticed that when you chew peppermint, sometimes your mouth starts to feel
cold? Well that’s because it contains menthol, a chemical which activates the body’s “cold receptors”
(TRPM8 if you’re interested). Funnily enough, the effect lasts even after you
have finished the gum, thanks to a phenomenon known as “sensitisation”. That’s
why hot drinks feel so strange in your mouth after chewing gum.
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- Chilli peppers: these contain
the chemical capsaicin – this activates receptors which detect warmth.
- Fish: did you know there’s a fish that
can actually make you think hot is cold and cold is hot? Yep that’s
right, apparently the phenomenon works through the ciguatoxin poison – a neurotoxin
which can be released by a range of tropical fish. So what does it do? Well
according to several sources it causes “hot-cold reversal”: to understand what
this means, just imagine you are back in 1774. Sailing under Captain James Cook
in the Pacific, the sky clear, the sea blue – all is well….and then you start
to notice something strange. Your face burns, your teeth feel like they are
about to fall out, hot is cold and cold is hot.. In short you have ciguatera – a non bacterial illness borne
by fish.
The exact mechanism for this hot-cold reversal continues to
be debat
ed, but some interesting neural studies have been published in case you
are interested in learning more.
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http://www.smithsonianmag.com/science-nature/why-does-very-hot-water-sometimes-feel-cold-180953532/#F8BOK3vfeCiTi3Ux.99
Cold + warm = hot?
In 1920 an article was published: “The Spatial Condition of the Fusion of Warmth
and Cold in heat”. Basically this is the idea that a simultaneous cold and warm
stimulus will be perceived by the body as heat.
Clinical relevance – Pathologic cold: Chronic pain
Patients with neuropathic pain often experience cold pain –
why? Apparently the reasons are still largely unknown, but here are some potential causes.
Causes of pathologic cold: signalling dysregulation
1. Neuronal
excitability/ sensitisation at the primary levels
2. Loss
of cold sensitivie fibres after central disinhibition
3. Loss
of cross-inhinition in the spnal cord
4. Neurological
conditions e.g. neuropathic pain.
Interested? Other questions to ponder….
1. 1. Why
does wet feel wet?: It turns out that our detection of temperature plays a key
role. “Researchers develop the first neurophysiological mode of how humans
sense wetness”
22. Why
are some people more sensitive to heat than others? One study has shown
evidence that cold perception has a heretable component. See the twin study….
“ Feeling of Cold Hands and Feet is a
Highly Heritable Phenotype”
33. Can
dogs suffer from frostbite? Dogs have a network of blood vessels which protects
them, keeping them warm in cold extremes.
44. Mechanisms
of heat pain in neuropathic pain.
5. Pain
pathways – hopefully the topic of my next post! J \
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