Opium has long been a drug of interest to scientists. It is one of the most effective of all pain killers. Opium has the serious disadvantage, however, of producing addiction in long-term users. Research on the mechanism by which opium works in the central nervous system has a double appeal. It provides information on the nature of pain and on drug addiction.
In 1973 an important breakthrough in this research occurred. Solomon Snyder and Candace Pert at Johns Hopkins School of Medicine in Baltimore, Maryland, discovered receptors on brain cells to which opium will bind. Receptors are molecular groups within the cells that have a special affinity for toxins. These receptors have come to be called opioid receptors. The term opioid is used for any type of chemical that behaves in a manner similar to that of opium.
Snyder and Pert found two locations in the central nervous system where opioid receptors are most common. One is in the spinal column. It is here that pain is first detected. The second in the medial thalamus of the brain, where chronic pain is often concentrated. Solomon and Pert hypothesized that opium locks into opioid receptors on a cell. It then slows the rate at which that cell can transmit a "pain" message. These two actions may also be responsible for the sense of euphoria (bliss, happiness) that accompanies opium use.
In later research, the natural function of opioid receptors was discovered. John Hughes and Hans Kosterlitz at the University of Aberdeen (Scotland) found the chemicals that occur naturally in the human body that also bind to opioid receptors. These enkephalins are an important part of the body's natural pain-fighting mechanism.
[See also Endorphin and enkephalin ]