ABSTRACT
Among drugs of abuse, opiates such as morphine and heroin certainly occupy a preponderant position as they have been abused for a millennium and still constitute a major social problem on the eve of the twenty-first century. Surprisingly, and in spite of major research efforts, rather limited pertinent scientific information is currently available on mechanisms leading to tolerance and dependence to opioid derivatives in human. The existence of another class of opioid sites, sigma, was originally proposed but it now appears that these sites are of a non-opioid nature since various antagonists including naloxone cannot block sigma-related effects. Interestingly, sigma receptors may be related to psychotomimetic effects induced by various drugs of abuse including benzomorphans and phencyclidine. In order to establish the characteristics of the various classes of opioid binding sites present in the human brain, the authors evaluated receptor binding parameters in membrane homogenates.
