Opiate receptors and opioid peptides: "The poppies of the mind"

In 1964 β-lipotropin, a compound consisting of 91 amino acids, was isolated from the adenohypophysis. In 1973, opiate receptors were found to be present in different areas of the brain and it was postulated that the brain probably produces opiate-like substances which react with these receptors. This finding was followed with an intensive search for opiate-like substances, resulting in the isolation of two groups of substances which react with the opiate receptors. These were named the encephalins and the endorphins. All members of these two groups were either peptides or polypeptides and the amino-acid sequence of each corresponded to the amino-acid sequence of specific segments of β-lipotropin.