Abstract

The possibility that immunological mechanisms are involved in the development of tolerance to the analgesic effect of morphine was investigated, focusing on several immunological parameters. The data indicate that transfer of spleen cells and bone marrow cells obtained from morphine-tolerant donors into nontolerant syngeneic recipient mice did not result in the transfer of tolerance to the analgesic activity of morphine. Furthermore, the data indicate that the thymus, which is essential for the immunological response to many antigens, was not involved in the induction of tolerance to the opiate since tolerance was induced in thymectomized mice as well as in genetically athymic mice. The results suggest that immunological factors do not seem to play a crucial role in the phenomenon of tolerance to the analgesic activity of morphine.