Understanding the dysphoric states of morphine withdrawal by monitoring intra-cellular events

Abstract

In drug research, it is extremely important to predict or understand the side effects after chronic treatment with a drug. In this workshop, we would like to demonstrate the withdrawal symptom-like changes within cells after chronic stimulation of μ-opioid receptor type 1C (MOR-1C). We examined the changes in the spatiotemporal localization of endoplasmic reticulum （ER） and mitochondria in CHO cells under the abrupt cessation of MOR-1C activation. Visualized mitochondria and ER were diffusely distributed in the cytoplasm. Chronic morphine treatment did not cause any change in the localization of mitochondria in cells. In contrast, the abrupt cessation of MOR-1C stimulation by naloxone produced mitochondrial translocation and clustering at the perinuclear region of cells. The distribution of the ER did not appear to be affected by the same treatment. The abrupt withdrawal from MOR-1C stimulation induced Ca²⁺ influx through Ca²⁺ channels (e.g., voltage-dependent anion channel 1, IP₃ receptor and ryanodine receptor) to the mitochondria accompanied by a decrease in mitochondrial membrane potential. We also confirmed that withdrawal diarrhea after chronic treatment with morphine was completely suppressed by combination with an IP₃ receptor antagonist and a ryanodine receptor antagonist in mice, indicating that withdrawal of chronic stimulation of MOR causes dysphoric states in individuals as well as cells through Ca²⁺ dynamics between mitochondria and ER accompanied by changes in the morphology of mitochondria. Thus, evaluation of intracellular events after chronic drug treatment for adaptation within cells is quite informative for understanding the maintenance mechanisms of biological homeostasis.