ABSTRACT
The use of opium can be traced back at least to 4500 BC, when early Egyptian images and Sumerian texts depict its use both medicinally and for religious purposes. The pharmacologically active compounds in opium are principally morphine, codeine, and thebaine alkaloids. The opiates have a complex spectrum of effects on neural activity that include analgesia, euphoria, and respiratory depression. This chapter examines these mechanisms of action. It first looks at the neural pathways for pain sensation and analgesia. While brainstem mechanisms clearly mediate pain signaling, several cortical structures are implicated in pain perception. The identification and distribution of opiate receptors and their endogenous ligands began in the early 1970s. The chapter also discusses the mechanisms of opiate reinforcement, opiate tolerance, as well as opiate agonists and antagonists. The Center for Disease Control (CDC) estimates that approximately one million people in the US are currently dependent on heroin or other opiates, including oxycontin and hydrocodone.
