Opioid receptors and pain.

A receptor site is considered to be a transducing factor for effect of the natural ligand. Endorphins and the drugs that mimic their effects (the opiates) are important for analgesia, and consequently the receptor sites involved in actions of opioid drugs are to be considered as relevant to the transmission of pain. The present review describes the distribution of the opioid receptor sites in the central nervous system, and links their presence to pain-specific areas of the central nervous system.