Stavinoha_1977_Arch.Int.Pharmacodyn.Ther_225_58

Implantation of a 75 mg morphine tablet in mice caused a significant decrease in the body weight and hypothermia. After 3 days, the concentration of acetylcholine decreased in all brain regions with the exception of the cerebellum. A significant decrease in acetylcholine content was observed in the midbrain, corpus striatum and the cerebral cortex 3 days after implantation. It is postulated that the decrease in Ach content is due to an increased release of acetylcholine as a result of development of tolerance to morphine.