Sugar-dependent rats show enhanced responding for sugar after abstinence: Evidence of a sugar deprivation effect

Studies have shown that intermittent sugar availability (12 h/day) produces signs of dependence in rats, including escalation of intake, mu-opioid and dopamine receptor changes, behavioral and neurochemical indices of withdrawal, and cross-sensitization with amphetamine. "Deprivation-effect" paradigms, whereby abstinence from a substance results in enhanced intake, are often used to measure "craving" for drugs of abuse, such as alcohol. The present study used operant conditioning to investigate consumption of sugar after abstinence in rats selected for glucose avidity. The experimental group was trained on a fixed ratio (FR-1) schedule for 25% glucose for 30 min/day for 28 days and also had glucose access in the home cages for an additional 11.5 h daily. The control group had only the 30-min/day access to glucose in the operant chambers. Then, both groups were deprived of glucose for 2 weeks. After this period of abstinence, animals were put back in the operant chambers. The experimental group responded significantly more than ever before, and significantly more than the control group. In conclusion, daily 12-h access to sugar, in the paradigm used, can result in an altered neural state that lasts throughout 2 weeks of abstinence, leading to enhanced intake. Together with previous results, this deprivation effect supports the theory that animals may become dependent on sugar under selected dietary circumstances. (c) 2005 Elsevier Inc. All rights reserved.