Exercise-induced morphine insensitivity is accompanied with a decrease in specific G-protein subunits gene expression in rats

► In exercise training animals, morphine cannot produce analgesic effect properly. ► G-protein subunits have a critical role in opioid effects at the cellular level. ► The levels of Gαi and Gβ expression decreased in the spinal cord of trained animals. ► This may be responsible for exercise-induced morphine insensitivity.