Thursday, July 25, 2013

Melzack & Katz, Pain. Part 17e: Stress and aging, keeping hippocampal dendrites fluffed up

The paper, Pain.

Part 17: The stress of it all Part 17b: Stress and adrenals Part 17c: Women, pain, and stress Part 17d: Stress, aging, and pain

Synopsis from yesterday

Stress is a Goldilocks, paradoxical kind of thing. You need a bit of it to learn anything, because the brain can't learn anything unless it's exposed to glucocorticoids, it seems. No stress at all and you could end up smart as an eggplant. 

Too much of it for too long though, you end up soaked in glucocorticoids, the cortisol will chew away at your physicality, and your hippocampus won't be able to control the hypothalamus. It will be the physiological equivalent of microphone squeal.

If the hippocampus can't tell the hypothalamus, "Thank you very much, I got it, I've learned what to do in this situation next time, so you can stop with the glucocorticoids already", the hypothalamus, like a dripping faucet, will just keep pouring the stuff out, which will just keep killing more and more of the body and prevent new baby cells from being born and raised in the hippocampus, which will make the hypothalamus drip faster, etc., etc. ... and then we will age very very quickly. 

All of a sudden.

I remember this happening to me at about age 37. For no very clear externally blameable reason, I suddenly began to feel as though I was under inescapable stress. I went grey, needed glasses, became peri-menopausal, gained thirty pounds and began crying for no reason, out of the blue. In the space of just a couple months with no change in life on the outside, on the inside I felt a huge cave-in happen, and my physicality changed, just like that. After struggling for about a year on my own, I finally went for some psychotherapy, dealt with a few personal issues, and whether that helped or it was merely coincidental, I started to feel better and my inside life went on again. I chalked it up to one of those depressive episodes I get once in awhile and just live through. It was the worst one ever, though. The one I survived few years ago was pale by comparison.  

[Never ever managed to lose the extra weight - it must be my cortisol blotter.]

If you don't "move it" you'll lose a lot of brain power in the hippocampus, which, by the sound of it, relies on neurogenesis and neuroplasticity to regulate other things, because, again by the sound of it, maybe its neurons just wear out and need replacing. Exercise makes brain-derived neurotrophic factor, BDNF. BDNF helps new baby brain cells develop, but even more strategically, it helps already existing brain cells develop more dendrites, and already existing dendrites develop a thicker, fluffier, spinier surface area. More surface area, better communication. 


Melzack and Katz continue, in the section to do with pain and stress: 
"The cortisol output by itself may not be sufficient to cause any of these problems, but rather provides the conditions so that other contributing factors may, all together, produce them. Sex-related hormones, genetic predispositions, psychological stresses derived from social competition, and the hassles of everyday life may act together to influence cortisol release, its amount and pattern, and the effects of the target organs."

Like too much salt in the soup, it can ruin the entire batch.
These speculations are supported by strong evidence. Chrousos and Gold70 have documented the effects of dysregulation of the cortisol system: effects on muscle and bone, to which they attribute fibromyalgia, rheumatoid arthritis, and chronic fatigue syndrome. They propose that they are caused by hypocortisolism, which could be due to depletion of cortisol as a result of prolonged stress. Indeed, Sapolsky71 attributes myopathy, bone decalcification, fatigue, and accelerated neural degeneration during aging to prolonged exposure to stress."
Hmmnn... hy-PO-cortisolism? Depletion
OK, I don't quite get this - it will require digging up and reading Chrousos and Gold to see what they are talking about. 
Chrousos GPGold PW. The concepts of stress and stress system disorders. Overview of physical and behavioral homeostasis.JAMA 1992267:12441252.

This might take awhile. Another place to land, rest from our ride down the river, get out and stretch. This looks like a nice safe place to tie up the boat for awhile. 


Blogus Interruptus
I'm off to teach in Minneapolis for a few days. I'll resume the blog-saga when I return, next week. 

Previous blogposts

Part 1 First two sentences Part 2 Pain is personal Also Pain is Personal addendum., Neurotags! Pain is Personal, Always.

Part 3a Pain is more than sensation: Backdrop Part 3b Pain is not receptor stimulation Part 3c: Pain depends on everything ever experienced by an individual

Part 4: Pain is a multidimensional experience across time

Part 5: Pain and purpose

Part 6a: Descartes and his era; Part 6b: History of pain - what’s in “Ref 4”?; Part 6c: History of pain, Ref 4, cont.. : There is no pain matrix, only a neuromatrix; Part 6d: History of Pain: Final takedown Part 6e: Pattern theories in the history of pain Part 6f: Evaluation of pain theories Part 6g: History of Pain, the cautionary tale. Part 6h: Gate Control Theory.

Part 7: Gate control theory has stood the test of time: Patrick David Wall;  Part 7bGate control: "The theory was a leap of faith but it was right!"

Part 8: Beyond the gate: Self as mayor Part 8b: 3-ring circus of self Part 8c: Getting objective about subjectivity

Part 9: Phantom pain - in the brain! Part 9b: Dawn of the Neuromatrix model Part 9cNeuromatrix: MORE than just spinal projection areas in thalamus and cortex Part 9d: More about phantom body pain in paraplegics

Part 10: "We don't need a body to feel a body." Part 10b: Conclusion1: The brain generates its own experience of being in a body Part 10c:Conclusion 2: Your brain, not your body, tells you what you're feeling Part 10dConclusion 3: The brain's sense of "Self" can INclude missing parts, or EXclude actual parts, of the biological body Part 10eThe neural network that both comprises and moves "Self" is (only)modified by sensory experience

Part 11We need a new conceptual brain model! Part 11b: Intro to a new conceptual nervous system Part 11c: Older brain models just don't cut it Part 11d: The NEW brain model!

Part 12: Action! 12b: Examining the motor system, first pass. 12c: Motor output and nervous systems - where they EACH came from Part 12d... deeper and deeper into basal ganglia Part 12e: Still awfully deep in basal ganglia Part 12f: Surfacing out of basal ganglia Part 12gThe Action-Neuromatrix 

Part 13: Pain and Neuroplasticity Part 13b: Managing neuroplasticity

Part 14: Side trip out to the periphery! Part 14b: Prevention of pain neurotags is WAY easier than cure Part 14cPW Nathan was an interesting pain researcher  Part 14dBrain glia are from neuroectoderm and PNS glia are from neural crest Part 14e: The stars in our headsPart 14f: Gleeful about glia Part 14g: ERKs and MAPKs and pain Part 14h: glia-fication of nociceptive input 14i: molecular mediators large and small Part 14j: Neurons, calling glia (over, do you read?) Part 14k: Glia calling glia, over. Do you read? Part 14l: satellite cell and neuron cell body interactions, and we're outta here!

Part 15: Prevention of neurobiological hoarding behaviour by dorsal horn and DRG glia is easier than clutter-busting after the fact

Part 16: Apples are to fruit as cows are to animals as nociceptive input is to pain

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