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Questions regarding the endogenous opioid system

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JimRaynor

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Jan 25, 2012
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Despite extensive lurking on this forum and elsewhere am I still confused about the purpose of the endogenous opioid system in humans. In fact, the more I read the more confusing it gets.

For example, some claim that the opioid system activates during and after physical excertion. This seems reasonable at first glance, but when I consider the typical acute effects exercise has on me (increased appetite and appreciation of food, increased sexual drive being the most pronounced) they seem to be even opposite to that of opiates. I also stumbled over a source claiming that it is primarily the cannabinoid system that activates in response to exercise, which actually makes much more sense given the effects exercise has on me.

Other sources claim the opioid system activates as a response to injury or pain. And that doesn't seem to make much sense to me either. Firstly, injuries promotes hyperalgesia around the damaged tissue so as to discourage usage of the damaged bodypart until healing is done. Secondly the opioid system has reinforcing effects, and reinforcing behaviour that leads to injuries seems really counterproductive from a evolutionary perspective. There's also the thing about pain being a defensive mechanism enhancing survival. Why then have a system that counteracts this defensive mechanism? Doesn't seem to make much sense

And lastly some claim that the opioid system is activated during infection and other sicknesses, and that is confusing for me too. While being ill have I never experienced any effects at all resembling those typial of opiates. Quite the contrary infact, almost all activities imaginable are more painful than usual while having the flu. Then there is also the fact that opioid withdrawal gives flu-like symptoms, suggesting that opioid activity actually is diminshed during sickness, and not elevated.

I would be very grateful if someone could clarify my confusion regarding these matters. I am mostly intrested in the mu opioid receptors purpose in the endogenous opioid system and why and when the body activates that receptor in particular.
 
JimRaynor said:
Other sources claim the opioid system activates as a response to injury or pain. And that doesn't seem to make much sense to me either. Firstly, injuries promotes hyperalgesia around the damaged tissue so as to discourage usage of the damaged bodypart until healing is done. Secondly the opioid system has reinforcing effects, and reinforcing behaviour that leads to injuries seems really counterproductive from a evolutionary perspective. There's also the thing about pain being a defensive mechanism enhancing survival. Why then have a system that counteracts this defensive mechanism? Doesn't seem to make much sense
Click to expand...

Imagine a wounded animal that has to try to escape from a predator. In that case analgesia from endorphin release is useful as it prevents the animal being immobilized by the pain.

Endorphins have many physiological functions, for example in the vomiting mechanism. Activation of opioid receptors in the chemoreceptor trigger zone in the brain causes nausea.
 
polymath said:
Imagine a wounded animal that has to try to escape from a predator. In that case analgesia from endorphin release is useful as it prevents the animal being immobilized by the pain.

Endorphins have many physiological functions, for example in the vomiting mechanism. Activation of opioid receptors in the chemoreceptotrigger zone inthe brain causes nausea.
Click to expand...

Do you mean that endorphins are released as a part of the fight or flight response? I cannot really make any sense of that either.
Pain tolerance certainly is increasuring lifethreatening situations, but isn't that due to mainly the massive norepinephrine release? For instance amphetamine also does reduce pain. And wouldn't endorphins kinda take the edge of the panic from being chased by a predator, making the animal a little less motivated to escape? And wouldn't the euphoria from endorphin release make the animal to not put as much effort into avoiding similar situations in the future as they would have otherwise. It just doesn't add up to me.

And then we also have the physiological reactions to endorphins. How would being nauseous and throwing up help an injured animal trying to escape from a predator?
 
The endorphins may be released only in one specific area of the brain depending on the situation. All endorphin release doesn't cause euphoria or nausea, as it does not necessarily happen in the nucleus accumbens or the CTZ.
 
Your endogenous system works alot better than shooting up heroin. It very specifically releases endorphins, whereas some dope is gonna hit every opiod receptor up there. I know when I dislocated my shoulder, I got the same feelings as when I did too many percs my first time. I was nauseated, I was dizzy, my arm stopped hurting, and I had a big smile on my face for some reason. That would've been a massive endorphin release, and adrenaline was probably in there since I was mid lacrosse game. Although, self bioassay's don't really mean anything. It's kind of like saying "this is a serotininish drug," you can't determine that from introspection, and subjective effects... at all.
 
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