[Opiate receptors and endorphins at the central nervous system level]

Four years ago, sterospecific sites for the bending of opiates were discovered within the brain of animals and the human being. All of the properties of these sites are in conformity with the proposition that they are pharmacological receptors which have long been postulated for these drugs. The binding of morphine or of one of its derivatives to these sites should result in chemical or physical reactions leading to well known pharmacological responses. These reactions following the binding of drugs to the receptors are not yet known, but there is some evidence that cyclical nucleotides play a role. The affinity of a whole series of morphine derivatives, agonists and atagonists, is well correlated with their pharmacological effectiveness. In the presence of sodium salts, antagonists become more strongly bound and agonists less strongly than in the absence of sodium. The evidence is presented. This is explained by an equilibrium between two formations of the receptor: one characteristic of the absence of sodium and one of its presence. Receptors are found in the nervous system of all vertebrates and their distribution has been studied in the human brain. The regions with the highest concentration of receptors are those of the limbic system. A high level exists also in the "substantia gelatinosa" of the spinal cord, which is involved in the passage of painful messages. Study of the function of morphine receptors has led to the isolation, in animal brain, of a number of peptides with morphine properties named endorphines. The first two endorphines isolated were pentapeptides named encephalins. The properties of endorphines from the subject of several lecture in this course.