[Heterogeneity of mu- and delta-opioid active sites in the mouse cerebral cortex. Selective increase in the affinity of a superhigh affinity delta-site during long-term administration of morphine].

: The interaction of the selective mu-ligand [D-Ala2, MePhe4, Glyol5]enkephalin (DAMGO) and the selective delta-ligand [D-Ser2, Leu5, Thr6]enkephalin (DSLET) with the binding sites in rat brain cortex membranes, has been studied. Analysis of the binding isotherms in the presence and absence of nonlabelled DAMGO and DSLET revealed that these ligands can interact with both superhigh affinity and high affinity binding sites that are distinct from one another. Prolonged administration of morphine and formation of physical dependence caused no appreciable changes in the parameters of either the superhigh affinity binding sites for the mu-ligands or the high affinity binding sites for mu- and delta-ligands. At the same time, the affinity of the superhigh affinity site for delta-ligands increased 3.5 times (tau 1/2 approximately equal to 17.5 h).