How Does The Opioid System Control Pain, Reward And Addictive Behavior?

The opioid system controls pain, reward and addictive behaviors. Opioids exert their pharmacological actions through three opioid receptors, mu, delta and kappa whose genes have been cloned (Oprm, Oprd1 and Oprk1, respectively). Opioid receptors in the brain are activated by a family of endogenous peptides which are released by neurons. Opioid receptors can also be activated exogenously by alkaloid opiates, the prototype of which is morphine, which remains the most valuable painkiller in contemporary medicine.