Here is a link to previous musings, 1-6.
I'm not here to discuss me today, I'm here to introduce you to my sibling, TRP. TRP is a C, too. But TRP does something slightly different, which she will tell you all about: TRP, take it away.
Hi there. My name is TRPv1, but you can call me TRP. I'm a C-fibre, just like my peptidergic lil' sis, but I'm in a different group, for now. I respond to heat, and to capsaicin. Oh, and chronic constriction injury in nerves.
Here is the deal: If someone or something provokes me enough, I will fire. So don't provoke me. You do not want to provoke me. Here is what happens if you do.
Long story short, enough provocation will result, at my central terminal, in an increase in permeability of the blood-spinal cord barrier, and of the blood brain barrier, within... oh.. about 24 hours. Do you really want stuff leaking into your ascending pathways? Eyew, there are microglia and stuff in there. Eyew! Do you want the sorts of thing they excrete getting all over your pathways? I should think not. But it will happen. So don't provoke me. Consider yourselves fairly warned.
|Image from http://www.rehabresearch.ualberta.ca/spinalcordresearch/blood-brain-barrier|
Now, the reason this happens is because.. well, evolution. OK? I really don't have any better answer. Sorry.
And believe me when I say I don't really like when I vomit out through my central terminal and this happens to you. If you do not provoke me, it won't happen. So, don't get a sunburn, or burn yourself in any way, or rub your eyes after you've chopped up jalapeño peppers for your salsa. [The correct pronunciation is "Hah-la-PAIN*, yo.."]
And make sure you move all body parts around in all directions to keep your nerves slidey and healthy and not chronically constricted anywhere. Motion is lotion. Remember that. Get exercise.
Now, if it does happen, and I'm activated, the blood brain barrier and the blood spinal cord barrier open up and nasties flood in and the poor critter brain is terribly bothered, but the effect starts to fade after 48 hours, and by the end of a week, it reverses to normal. One hopes.
One hopes. One hopes the barriers come back such that the size of molecule they let through goes back to being just the teeny ones that the nervous system needs, not every annoying immune thing the ecosystem of the body has to passively or actively offer.
Maybe in some people, they don't. Because.. they can't. Now there's a thought.
Apparently this increased permeability effect doesn't extend to the cerebellum or the human brain. Just the critter brain. Which is big enough.. it's the whole brain stem, limbic system.. old bits of cortex..
So, that's good I guess. People are already crazy enough without their human brain being short-circuited by some blood brain barrier opening, directly, so it's good there is a separateness between the internal regulation system, one the one hand, and the human brain, on the other; it's good that the critter brain can make opioids etc. and it's good it can fix itself over time. Usually it learns how to do that...
It's good that humans and their human brains can distract themselves until the sunburn, or whatever, heals, or put lidocaine on, now that they have such a thing. (Poor humans, no fur to keep the rays off their skin..) It's good that humans still have human primate social groomers they can hire, to pull their body parts around a bit, maybe relieve chronic constriction in various nerves.
Anyway, that's me, TRPv1; it's been a pleasure to meet you - that's all for now.
* That is the correct pronunciation, but keep in mind that it's still only just nociception, not pain, until and unless the human brain experiences it, and suffers as a result of the experience. (Here is a handy tip: if you feel your fingers burning after chopping up peppers, or your mouth burning after eating them, milk takes away the sting. Do NOT touch your eyes.)
RESOURCES OPEN ACCESS (thank you to Sigurd Mikkelsen for linking this paper to Facebook):
, , and Peripheral nerve injury and TRPV1-expressing primary afferent C-fibers cause opening of the blood-brain barrier. Molecular Pain 2010, :74
Blood Brain Barrier Short You-tube video
Ethan A Winkler, Jesse D Sengillo, Robert D Bell, Joseph Wang, Berislav V Zlokovic; Blood–spinal cord barrier pericyte reductions contribute to increased capillary permeability. Journal of Cerebral Blood Flow & Metabolism (2012) 32, 1841–1852 (open access)