[The role of multiple opioid receptors and their ligands in pain modulation]

The multiplicity of opioid peptides (endorphins) present in the mammalian CNS finds a counterpart in the existence of various types of opioid receptors (mu, delta, kappa, epsilon). The various receptor types, which possess distinctive relationships to particular opioid peptides, play a distinctive role in pain modulation. At the cerebral level primarily mu- and probably epsilon-receptors, rather than kappa-receptors appear to be involved, and, at the spinal level, primarily mu- and kappa-receptors. The function of delta-receptors at both levels remains unclear. There is certain evidence that the various opioid receptor types (and corresponding ligands) are of variable significance in the control of pain dependent upon the nature of the nociceptive stimulus (e.g. thermal vs. pressure).