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The Material Basis of Emotion

I AM GOING TO DESCRIBE AN ARRAY of fascinating, mostly new findings about the chemical substances in the body called neuropeptides. Based on these findings, I am going to suggest that neuropeptides and their receptors form an information network within the body. Perhaps this suggestion sounds fairly innocuous, but its implications are far-reaching:

I believe that neuropeptides and their receptors are a key to understanding how mind and body are interconnected and how emotions can be manifested throughout the body. Indeed, the more we know about neuropeptides, the harder it is to think in the traditional terms of a mind and a body. It makes more and more sense to speak of a single integrated entity, a "body-mind."

Most of what I will describe are laboratory findings, hard science. But it is important to remember that the scientific study of psychology traditionally focuses on animal learning and cognition. This means that if you look in the index of recent textbooks on psychology, you are not likely to find a listing for "consciousness," "mind," or even "emotions." These subjects are basically not in the realm of traditional experimental psychology, which primarily studies behavior because it can be seen and measured.

The Specificity of Receptor Sites

There is one field in psychology where mind — at least consciousness — has been objectively studied for perhaps twenty years. This is the field of psychophar-macology wherein researchers have developed highly rigorous ways to measure the effects of drugs and altered states of consciousness.

Research in this field evolved from an assumption that no drug acts unless it is "fixed" — that is, somehow gets attached to the brain. And so researchers initially imagined hypothetical tissue constituents to which a drug might bind — much the way a key fits a lock — and they called these "receptors." In this way, the notion of specific brain receptors for drugs became a central theory in pharmacology. It is a very old idea.

In the past several years, a critical development has been the invention of new technologies for actually binding drugs to these receptor molecules and for studying both their distribution in the brain and body and their actual molecular structure.

My initial work in this area was in the laboratory of Solomon Snyder at Johns Hopkins University, where we focused our attention on opium, a drug that obviously alters consciousness and that also is used medicinally to alleviate pain. I worked long and hard, over many months of initial failure, to develop a technical system for measuring the material in the brain with which opium interacts to produce its effects. To make a long (and technical) story short, we used radioactive drug molecules, and with this technology were actually able to identify the receptor element for opium in the brain. You can imagine, therefore, a molecule of opium attaching itself to a receptor — and then from this small connection, large changes follow.

It next turned out that the whole class of drugs to which opium belongs — they are called opiates and they include morphine, codeine, and heroin, as well as opium attach to the same receptors. Further, we discovered that the receptors were scattered throughout not only the brain but also the body.

After finding the receptor for the external opiates, our thinking took another step. If the brain and the other parts of the body have a receptor for something taken from outside the body it makes sense to suppose that something produced inside the body also fits the receptor. Otherwise, why would the receptor be there?

This perspective ultimately led to the identification of one of the brain's own forms of opiates, a chemical substance called beta endorphin. Beta endorphin is created in the brain's own nerve cells and consists of peptides — thus it is a neuropeptide. Furthermore peptides grow directly off the DNA which stores the information to make our brains and bodies.

If you picture an ordinary nerve cell, you can visualize the general mechanism. In the center (as in any cell) is the DNA, and a direct printout of the DNA leads to the production of a neuropeptide, which then traverses down the axons of the nerve cell to be stored in little balls at the end waiting for the right electro-physical events that will release it. The DNA also leads to the production of receptors, which are made out of the same peptide material but are much bigger. What has to be added to this picture is the fact that 50 to 60 neuropeptides have been identified, each of them as specific as the beta endorphin neuropeptide. We have here an enormously complex system.