So I’ve been reading this book called “The Other Brain” by R.D. Fields, which I’ve been finding very interesting because it has a lot to do with glia cells and it’s relation to a number of different neurological disorders and diseases. This particular chapter that I read in regards to addiction, gave me an insight into just how important and influential glia cells are in addiction. I think we often tend to forget about glia cells and their importance. So in this chapter I was reading, it referred to heroin and alcohol addictions, mainly based on the fact that many famous people and musicians have been victims of these addictions (like Jimi Hendrix, Janis Joplin, Mick Jagger, Eric Clapton, John Lennon, etc). What I found interesting in this chapter was 2 things: 1) that John McCain’s wife was addicted to prescription narcotics after taking them originally to relieve pain (who knew?? I didn’t…), and 2) that this addiction to painkillers act the same way in the body and the brain as does heroin! So my question is why do doctors prescribe these narcotics when the chances of developing an addiction to them are relatively high? (I could totally be making a generalization here)
Fields describes an addiction to opiates as “the rainbow [that] truly ends in a vial of heroin” because it makes you so happy, and the “pursuit of happiness is life’s ultimate goal”. When using opiates, one builds a drug tolerance which results in the “brain fighting to adjust its circuits to restore the normal balance of activity against the pain-numbing effects of heroin as it suppresses activity in brain circuits involved with pain. ” I found this related to the homeostasis hypothesis that we went over in discussion, and how during withdrawal the brain is trying to compensate for the imbalance of drugs in the system that it has become so used to. In terms of the effects on the neurons, it appears that when exposed to opiates, the neurons become hyperactive for a prolonged period of time, so then more morphine or heroin is needed to suppress their activity again. It is this balancing act of activity of the neurons that makes drug dependence increase causing a need for circulation of the drug at all times in the neural circuitry. So when withdrawal occurs, the neurons in response to pain are no longer suppressed by the opiates anymore (heroin/morphine), and this is why withdrawal is so painful!
So how does this all relate to glia cells? Well apparently glia cells have opiate receptors as well, according to research done by Ronnback and Hansson in 1988. Supposedly morphine activates the opiate receptors on astrocytes which triggers them to release a number of substances that stimulates the pain circuitry in the brain; glutamate, nitric oxide, prostaglandins, and inflammatory cytokines increase activity whilst cholecytokinin and dynorphin inhibit action of morphine on pain receptors. It is possible, therefore, that “glia could be releasing the neural stimulants that counteract the nerve-damping effects of morphine, and thus contributing to morphine tolerance”. Even more so, glia cells increase the amount of opiate receptors on the cell membrane with an increased exposure to the drug.
Another study by Watkins et al. (2004) looked at addiction to morphine in rats and found that a chronic treatment of morphine increased the number of inflamatory cyotkines produced by glia. They then found that when morphine was administered to the rats with a drug that blocked the inflamatory cytokines receptors, “morphine suddenly became much more potent in relieving pain because glial countermeasures against the numbing actions of morphine were suppressed.” As such, the drug tolerance was eliminated. It appears that the rats suffered far less when the cytokine receptors were blocked, which would make the withdrawal from opiates a lot less daunting then it has been seen before. It is possible that this could be a new treatment in kicking drug addictions to opiates!