Several drugs of abuse appear to produce their pharmacologic effects by interacting with constituents of the cytoplasmic membrane and modifying its function. It will be determined whether the interaction of opiates with membrane constituents observed in vitro represents the drug receptor interaction occurring in vivo which ultimately leads to manifestations of the pharmacologic actions of these agents. This will be performed by comparing the effects of various ligands to alter opiate binding to brain slices in vitro with the effects of same ligands to influence the action of opiate agonists and antagonists on acetylcholine release from brain slices. Changes in the potency of opiate agonists and antagonists during the development and the loss of tolerance to morphine caused by chronic morphine treatment and following withdrawal will be examined and compared with the alterations in affinity of saturable binding sites for morphine, etorphine and naloxone in brain slices. If it is determined that the interaction of opiates with membrane constituents observed in vitro represents the drug receptor interaction, then possible changes in membrane function resulting from such an interaction will be explored. The proposed project, if successful, will elucidate the mechanism for the pharmacologic action of opiates and also the mechanism for the development of tolerance to these agents.