OPIATE EFFECTS ON THE BRAIN AND THE REST OF THE BODY

OPIATE EFFECTS ON THE BRAIN AND THE REST OF THE BODY

Morphine hits the backs of the legs first, then the back of the neck, a spreading wave of relaxation slackening the muscle away from the bones so that you seem to float without outlines, like lying in warm salt water. As this relaxing wave spread through my tissues, I experienced a strong feeling of fear. I had the feeling that some horrible image was just beyond the field of vision, moving, as I turned my head so that I never quite saw it. I felt nauseous. A series of pictures passed, like watching a movie: a huge neon-lighted cocktail bar that got larger and larger until streets, traffic and street repairs were included in it; a wait­ress carrying a skull on a tray; stars in the clear sky. The physical impact of the fear of death; the shutting off of breath; the stopping of blood. I dozed off and woke up with a start of fear. Next morning I vomited and felt sick until noon.

The character in William Burroughs's novel Junkie describes his first experience with morphine fairly accurately. 'the only thing missing from this description is the rush that comes with intravenous injection that most users compare to orgasm.

All opiates cause a pleasant, drowsy state in which all cares are forgot­ten (nodding off), and there is a decreased sensation of pain (analgesia). The feelings are the most intense after injection, which brings the rush. After the orgasmic feeling, sexual feelings usually diminish, and people experience decreased sexual desire and performance. This happens because opiates affect the release of many hormones and neurotransmit­ters, including those involved in the regulation of sexual behavior. People under the influence of opiates will often say that they just don't worry about their troubles anymore: they are in a special, safe place where cares are forgotten. The allure is understandable, and at the beginning it is impossible to understand the misery of addiction and withdrawal.

While the opiate user is in a dreamy, pleasant state, breathing slows, pupils are constricted, and he typically experiences nausea and perhaps even vomits. Although the effects on breathing can be quite dangerous, the other physiologic effects are fairly benign. For example, opiates do not produce big changes in blood pressure in healthy individuals. Most of the effects of narcotic drugs are caused by effects of the drugs on specific opi­ate receptors in the parts of the brain involved with the control of breath­ing and other involuntary functions. For example, opiate users vomit because morphine stimulates a center in the brain (the chemoreceptor trigger zone) whose job it is to cause vomiting in response to the ingestion of a toxic substance. So, in the movie Pulp Fiction the injection of adrena­line into the heart to reverse opiate overdose was not accurate. The effects on breathing that were causing the woman to OD were happening in the brain, and injecting a drug directly into the heart to get it started again was good theater, but bad pharmacology. Injecting an opiate receptorblocking drug (naloxone, or Narcan) into the bloodstream instead would have effectively treated the OD. The movie Trainspotting does a much bet­ter job of depicting the reversal of opiate effects with naloxone. The protag­onist is dumped at the doors of a hospital emergency room, taken into a room, and given naloxone. In a matter of seconds he leaps up from the gurney.

One very important effect of opiates on the body has made life easier for generations of foreign travelers. Opiates increase the tension in certain muscles in the gastrointestinal tract so that the normal propulsive move­ments that move food along cannot operate effectively—hence their well-known ability to cause constipation. This can be a good thing if you are in Mexico and have traveler's diarrhea. Diphenoxylate (Lomotil) takes advantage of a neat chemical trick to stop diarrhea without affecting the brain. The typical opiate molecule is slightly changed so that it is not fat-soluble enough to enter the brain. This gives you a very safe, very effec­tive medicine that can treat mild diarrhea without the risk of addiction. Through a similar action, opiates constrict the muscles of the urinary bladder and can cause difficulties in urination.

There is active research ongoing to use a similar strategy to develop drugs that bind to one special population of mu receptors that are not behind the blood-brain barrier but still involved in suppressing pain. This could be the holy grail of narcotics research—a nonaddictive nar­cotic drug.