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The addicted brain is different from the non-addicted brain. Heroin (and other opioids) alter expression of specific genes in specific brain regions resulting in neurochemical and behavioral changes. Because these changes are in the brain structure itself, according to Alan Leshner, the former director of NIDA, addiction is fundamentally, a brain disease; it is also heritable, with heroin addiction having the largest heritable component of any other addictions, says Dr. Mary Jeanne Kreek, a specialist in opiate addiction at Rockefeller University in New York, “up to 54% of heroin addictions seem to be on a genetic basis or a heritable basis.”
In the body, heroin is rapidly converted to morphine. Morphine is a “pure mu agonist:” it latches onto the mu endorphin receptors, and activates them (see box). These are the same receptors that our bodies’ endogenous opioids (endorphins) bind to. However, endogenous opiates are not addicting because they are rapidly destroyed by our own bodies’ enzymes so they are never in contact with the receptors long enough to induce tolerance.
Naloxone (Narcan) Displaces Morphine at the Mu Receptor, Reversing the Effects of Heroin Overdose.
Reversing a Heroin Overdose
As shown in the diagram, if naloxone is introduced to a morphine-bound receptor, it will kick morphine out of the receptor because it has a higher affinity for the receptor. It does not stimulate the receptor because it does not sit in the activation zone, therefore, it is considered to be an opioid antagonist.
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Heroin Addiction is a Disease with a High Genetic Component
While there have been attempts to develop pain management drugs derived from endorphin derivatives, they have not been superior to morphine or even as good as morphine. Even our brain’s own “morphine” is not as good as morphine. Nothing, so far, is as good as morphine.
Therefore, we are evolutionarily designed to enjoy these receptors being activated and to continue behaviors that activate them. Any powerful receptor-activating drug, such as heroin/morphine is fooling Mother Nature. These drugs stimulate this “brain reward” pathway (activating the (opioid) receptors) leading the user to seek further use in order to keep them activated.
Mu Endorphin/Opioid Receptors and Some Occupants
HEROIN, ADDICTION, AND OUR BRAIN
Our brain reward pathway is made of neurons that release chemicals (endorphins) when they are stimulated. These endorphins are released when we exhibit "survival behaviors:" (eating, drinking, sex, etc.). These endorphins bind to (opioid) receptors and lead to feelings of well-being so that we are driven to continue to engage in behaviors that guarantee our species’ survival.
The Mechanism of Heroin Addiction
mu opioid receptor
Typically, heroin and morphine kill by means of overdose. In part this is due to the fact that there is a small difference between the therapeutic dose (the amount for the desired effect) and the overdose. In overdose, the opiate receptor-rich area of the brainstem that controls respiratory reflexes, becomes flooded with morphine causing breathing to be severely depressed; the user dies by asphyxiation.
Humankind is susceptible to drug abuse because of how the reward pathways of our central nervous system are designed.
Receptor Activation zone
Opioids for Pain Management
The mu endorphin receptors can be occupied or unoccupied. If occupied by a full mu opioid agonist such as morphine (converted from heroin in the body), it will be fully activated as shown in red in the diagram below.
Naloxone, an antidote for heroin overdose, shown in yellow, binds more tightly to the mu receptor than morphine but does not sit in the activation zone so it does not stimulate the receptor at all and, therefore, it is considered to be a mu opioid antagonist.
Help for Heroin Overdose
Our Bodies are Designed to be Susceptible to Drug Abuse
One of the hallmarks of opium/heroin addiction is rapid cellular tolerance, where the brain cells cease being stimulated by the same dose of the drug.
mu opioid receptor
How Does Heroin Kill
And Requires Unique Treatment
If administered right away, naloxone can reverse the overdose. Naloxone has a higher affinity than morphine for the mu receptors but does not activate them. Therefore naloxone can bump morphine off of the receptors and occupy them without activating them. (see box)
Heroin, in the addicted individual, hijacks the brain’s reward system creating a runaway appetite for non-stop stimulation of the reward pathway. This person does not need to have hardships or other outside pressures for drug addiction to blossom. What the substance itself does to the brain of people who are biologically vulnerable is enough for addiction to take hold.