RESUMEN
The medicinal use of opium and of morphine in different cultures and ancient civilizations is described. Research within the past 40 years have demonstrated the existence of brain opiate receptors. Morphine and related opioid analgetic interact at these sites in the nervous system to produce the characteristic pharmacological effects of these drugs. The opiate receptors have structural homologies with a variety of other cell membrane recpetors; they activate second messenger-based chemical transduction systems in the cell embrane and are endowed with several regulation mechanisms. These opiate receptors are presumably activated under specific physiological conditions by endogenous ligands (opiopeptins). It is currently thought thar morphine mimicks the opiopeptins by interacting with these receptors either at different molecular subsites or with a different mode of action