Evidence that intermittent, excessive sugar intake causes endogenous opioid dependence

Objective: The goal was to determine whether withdrawal from sugar can cause signs of opioid dependence. Because palatable food stimulates neural systems that are implicated in drug addiction, it was hypothesized that intermittent, excessive sugar intake might create dependency, as indicated by withdrawal signs. Research Methods and Procedures: Male rats were food-deprived for 12 hours daily, including 4 hours in the early dark, and then offered highly palatable 25% glucose in addition to chow for the next 12 hours. Withdrawal was induced by naloxone or food deprivation. Withdrawal signs were measured by observation, ultrasonic recordings, elevated plus maze tests, and in vivo microdialysis. Results: Naloxone (20 mg/kg intraperitoneally) caused somatic signs, such as teeth chattering, forepaw tremor, and head shakes. Food deprivation for 24 hours caused spontaneous withdrawal signs, such as teeth chattering. Naloxone (3 mg/kg subcutaneously) caused reduced time on the exposed arm of an elevated plus maze, where again significant teeth chattering was recorded. The plus maze anxiety effect was replicated with four control groups for comparison. Accumbens microdialysis revealed that naloxone (10 and 20 mg/kg intraperitoneally) decreased extracellular dopamine (DA), while dose-dependently increasing acetylcholine (ACh). The naloxone-induced DA/ACh imbalance was replicated with 10% sucrose and 3 mg/kg naloxone subcutaneously. Discussion: Repeated, excessive intake of sugar created a state in which an opioid antagonist caused behavioral and neurochemical signs of opioid withdrawal. The indices of anxiety and DA/ACh imbalance were qualitatively similar to withdrawal from morphine or nicotine, suggesting that the rats had become sugar-dependent.