Pondering the addictive profile of opiates...

[bcubed]

Okay, so I've been tossing this around in my head...opiates work by activating the body's endogenous opiate receptors, meaning that opiate-like chemicals--endorphins--are used by the body to supress pain, reward certain behaviors, etc...which is most likely old news to all reading.

Well, that's certainly not unique to opiates...a great number of drugs act by mimicking naturally-occuring chemicals, or cause more (or less) of these chemicals to occur in the body. What seems to be unique to the opiates is the rapidity of the development of tolerance, physical dependance, and rebound effects (in other words, their strong "addictive profile.")

This makes me think: it's almost as if the body is trying to cause these effects to happen so quickly. Which then leads to the next thought: there must be some advantage to being "quick to addiction" for opiates and/or endorphins! (Meaning that being easily addicted confers some evolutionary benefit.)

This makes me wonder a. if this is so, and b. what advantage might be conferred here. The only thing that readily comes to mind is that rapid tolerance of endorphins would tend to put the kibosh on self-harming acts--i.e. beating one's self up for the endorphin rush.

That seems a little speculative, though...anyone want to take this thought and run with it?

[Gradient]

bcubed,

Cool topic! I'd only run a little bit further. Instead of conceiving the brain/body as endeavoring to do something on their own, allow me to suggest an alternative role for the brain. I've heard many people call the brain an organ dedicated to the production, maintenance, and adaptation of homeostasis for an organism's body - presented a myriad of varied stimuli. The more complex the organism's nervous system, the more varied its abilities will be in adapting, and therefore will exhibit more complex behaviors in expression of adaptation to changing environmental conditions.

Environmental conditions needn't be restricted to the actual external environment; neurochemical levels also present a dynamic, ever-changing environment in which neurons respond differentially to different amounts/proportions of neurotransmitters. Therefore, just as bcubed wrote, ingesting a substance that mimics one of the body's endogenous neurotransmitters (morphine mimicking endorphins, for example) serves to alter the environment that characterizes one's brain. The brain will thus function to change it's structure and pattern of impulse firing to compensate for this change in environment - with the end product of generating typical neuronal activity, despite persistent presence of a drug (the development of tolerance to a substance). Keep in mind: the brain has multiple 'reward' pathways, and therefore can produce many different kinds of reward given different circumstances - this translates to different kinds of addictions, depending on the particular substance regularly ingested. Cocaine, for example, is considered quite rewarding, and operates via dopaminergic pathways. Heroin, however, is also known to be quite rewarding, and operates via opioid activity, as bcubed pointed out. Clearly these are two different reward pathways 'hijacked' when ingested, which will be recruited in different circumstances when exposed to different stimuli.

I think that you're absolutely correct in considering this to be evolutionarily advantageous (however inconvenient!). In fact, it's one of the things that has rendered our species to be one of the most adaptable on the planet. Our brains are capable of actually changing their physical structure to accomodate changes in environment in order to produce the best possible (evolutionarily) behaviors. Also, it's complex enough to produce such a wide repertoire of behaviors that we can barely pin down what the best approach to addiction is - it's so different for everyone because everyone's brain will change differently given each individual's different genotype.
It isn't evolutionarily advantageous given the paradigm of natural selection, given our evolutionary genetic history, to constantly feel rewarded at all times. Imagine an adolescent ape, feeling the equivalent of a large dose of heroin, exposed to a lion (I don't know what the hell eats apes). Its reaction wouldn't be as appropriate - an immediate fight or flight reaction - as it would have been with typical neurochemical conditions. Opiates (sedatives as well) have been shown to lengthen the amount of time required for the expression of aversion from a negative or threatening stimulus. Therefore, having an organ that is capable of modulating the chemicals that underlie the expression of such behaviors would be ideal. Our brains our pretty amazing, in this respect - almost like the perfect mass of proteins for the job of keeping our bodies as in sync with the environment as possible. These changes in the brain are often referred to as neuroplastic changes, or neuroplasticity, if you're interested in further reading.

I'd love to read some of the community's ideas on the subject!