Morphine attenuates frustration-like behavior induced by sucrose reward deprivation in rats

In this study, a T-maze-based frustration model in rats was established using sucrose-reward de- privation. The results revealed that rats maintained a 75% preference for the sucrose-reward arm in the reward phase. During the sucrose-deprivation frustration phase, both the preference for the sucrose-deprivation arm (62.5%) and time spent waiting in the sucrose-deprivation arm decreased. Acute injection of morphine increased the preference in a dose-dependent fashion, and prolonged the waiting duration in the sucrose-deprivation arm. These findings indicate that morphine specifically inhibited the frustration response induced by sucrose reward deprivation. To further elucidate the pharmacological mechanisms involved, the opioid receptor antagonist naloxone was given to model rats prior to the injection of morphine. The results revealed that naloxone administration markedly attenuated the anti-frustration-like effects of 3 mg/kg morphine treatment. These findings suggest that morphine attenuates the frustration-like response to reward deprivation in rats through the opioid receptor.