For the past couple of weeks, we have been discussing the chemistry of the brain and how it impacts the mind. One could make the argument our thoughts are nothing more than a reflection of the collection of neurotransmitters diffusing through our synapses. However, it is generally accepted the mind is more than just that.
But a lot has been learned about how our minds work by studying the interaction of chemical compounds with our brains. Indeed, people have been experimenting with mind altering experiences for all of human history. Writings from Sumeria around 4000 BCE describe the pharmacological effects of the poppy plant or papaver somniferum.
Indeed, the opium derived from poppy seeds has been used for its psychoactive effects longer than any other agent except maybe alcohol. Over the course of human history, many physicians have employed or recommended opium and, at times, it has been viewed as a godsend.
Thomas Sydenham, one of the greatest physicians of the late seventeenth century, is quoted as saying: "I cannot forebear mentioning with gratitude the goodness of the Supreme Being, who has supplied afflicted mankind with opiates for their relief; no other remedy being equally powerful to overcome a great number of diseases, or to eradicate them effectually."
However, other physicians warned of the dangers of the drugs. Dr. John Jones went so far as to write: "The effects of suddenly leaving off the use of opium after a long use thereof are great and even intolerable distresses, anxieties, and depression of the spirit which commonly end in a most miserable death, attended with strange agonies, unless men return to the use of opium; which soon raises them again and restores them."
The opiates are powerful drugs. Their major component, morphine, has been prescribed for pain relief from the time of Hippocrates to modern day. Its derivative, heroin, is even more effective at pain relief and was once found in common medicines for coughs until its addictive potential was fully realized.
Discovering exactly what the opiates do to our brains and minds was not a simple task. The pharmacologists studying opiates and the brain determined the effects correlated with changes in the levels of all known neurotransmitters.
The effectiveness or potency of the opiates seemed to argue for binding to specific neuro-receptors. For example, the opiate etorphine can have effects at doses of less than a milligram or an amount smaller than a grain of salt. Such potency argues for a perfect fit into a receptor site.
Further evidence opiates act on specific receptors was provided by the existence of opiate antagonists. These are drugs which can dramatically reverse the effects of opiates, such as heroin, which kill by depressing the breathing function. Patients can be revived, even from deep comas and near death, by the injection of small quantities of the antagonist naloxone. In a very short time, naloxone is able to push the opiate molecules off their receptors sites and allow normal nerve function to resume.
Antagonists have been critical to brain research but perhaps more critical in emergency medicine. To understand how they work, one must consider what an agonist does which is to act at a receptor site in a manner which changes a bodily function in a measurable way. In the case of opiates agonists, they change the ability to detect pain while inducing a sense of euphoria or well-being.
The antagonists displace the opiates from the receptor site blocking any further agonist activity but, more importantly, they do so without generating any of the physiological changes.
Essentially, an antagonist such as naloxone is anti-morphine or anti-heroin. In the case of the modern drug epidemic, it is even anti-fentanyl as it is able to displace the drug from neuro-receptor sites. Unfortunately, because fentanyl is so effectively bound, it often takes much more naloxone to reverse its effects than any of the natural opiates.
Of course, the real question is why do the compounds found in the seeds of plant have an effect on our brain? The answer was found in 1973 when Candace Pert and Solomon Snyder at John Hopkis, Lars Terenius in Sweden, and Eric Simon in New York were all able to isolate opiate specific receptor sites in brain membranes using radioactively labelled antagonists. With the receptor membranes in hand, scientists were able to show that two naturally occurring five amino-acid peptides were the naturally occurring molecules which bound to these sites.
Called endorphins, for endogenous morphine-like substances, these compounds have been shown to regulate pain responses at the level of the spinal cord within the substantia gelatinosa. Specifically, when released, they block receptors on the transmitting axon and prevent the pain signal from ever reaching the synapse.
While drug overdoses are a societal scourge, opiates have also proven invaluable tools for investigating the function of the brain.