Decrease in the number of high-affinity opiate binding sites during the aging process in Mytilus edulis (Bivalvia).

As Mytilus edulis (Bivalvia) ages, the number of stereospecific opiate binding sites in the visceral ganglia significantly decreases. The number of high-affinity etorphine sites decreased by 30%; the number of naloxone sites decreased by 23%. The affinity of the ligands did not vary with age. In addition, the augmentation by opioids of dopamine levels in the visceral ganglia was less in older animals and was accompanied by a reduced sensitivity of the ganglia to etorphine and DAMA (D-Ala2,Met5-enkephalin-amide).