Stress-Induced Analgesia
“hot-plate test,” Put a rat on a hot plate; then turn it on. Carefully time how long it takes for the rat to feel the first smidgen of discomfort, when it picks up its foot for the first time (at which point the rat is removed from the hot plate). Now do the same thing to a rat that has been stressed—forced to swim in a tank of water, exposed to the smell of a cat, whatever. It will take longer for this rat to notice the heat of the plate: stress-induced analgesia. (Location 3230)
opiate drugs bound to specific opiate receptors in the brain. And these receptors tended to be located in the parts of the brain that process pain perception. This turned out to solve the problem of how opiate drugs block pain—they activate those descending pathways that blunt the sensitivity of the X neuron shown in the illustration. (Location 3237)
in three different classes—enkephalins, dynorphins, and the most famous of them all, endorphins (a contraction for “endogenous morphines”). The opiate receptors were discovered to bind these endogenous opioid compounds, just as predicted. Furthermore, the opioids were synthesized and released in parts of the brain that regulated pain perception, and they would make some of the neurons that relay pain signals in the spine less excitable. (Location 3244)
Acupuncture stimulates the release of large quantities of endogenous opioids, for reasons no one really understands. The best demonstration of this is what is called a subtraction experiment: block the activity of endogenous opioids by using a drug that blocks the opiate receptor (most commonly a drug called naloxone). When such a receptor is blocked, acupuncture no longer effectively dulls the perception of pain. (Location 3260)
- IV infusion of painkillers is more effective if the patient sees the infusion occurring than if it is done on the sly—knowing that a pain-reducing procedure is being carried out adds to its effectiveness. (Location 3274)
- Not surprisingly, it turns out that they work by releasing endogenous opioids. As but one example of the evidence for that, block opiate receptors with naloxone, and placebos no longer work. (Location 3279)
- stress triggers the release of one type of endorphin, beta-endorphin, from the pituitary gland. The rest is history. We all know about the famed runner’s high that kicks in after about half an hour and creates that glowing, irrational euphoria, just because the pain has gone away. During exercise, beta-endorphin pours out of the pituitary gland, finally building up to levels in the bloodstream around the 30-minute mark that will cause analgesia. The other opiates, especially the enkephalins, are mobilized as well, mostly within the brain and spine. They activate the descending pathway originating in the brain to shut off the X neurons in the spinal cord, and they work directly at the spinal cord to accomplish the same thing. Moreover, they also work at the pain receptors in the skin and organs, blunting their sensitivity. (Location 3283)
see also
Tags: science medicine biology
Superlink: 091 🏃Body and Medicine, 090 🌱Biology, 051 ☣Neurobiology
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Created: 17-09-22 16:23