Soon after the description of the molecular structure of opioid receptors our understanding of this regulatory system has improved greatly. The determination of the regions and amino acid residues involved in ligand binding to μ, δ and κ opioid receptors have been achieved. The binding profiles exhibited by the ligands on the receptors are not coincident, but display differences that are mostly evident for small molecules like morphine respect to opioid peptides. Moreover, agonists and antagonists also show differences in their pattern of interaction with these opioid receptors. In general, antagonists′ determinants are diffuse and extend over a wide region of the receptor protein. The involvement of the cloned opioid receptors μ, δ, κ in analgesia has been determined by means of in vivo injection of antibodies and antisense oligodeoxynucleotides directed to the receptor proteins or their respective mRNA. Using this strategy the classes of G-transducer proteins regulated by each type/subtype of opioid receptors to promote antinociception could be characterized. Opioid after displaying different patterns of binding to their receptors might trigger a variety of intracellular signals. The physiological implications and therapeutic potential of these findings merit consideration.

Peer Reviewed