Abstract
In rodents, sucrose has been found to elicit addictive-like behaviours like the development of tolerance and the association with cues present at the time of consumption. Furthermore, the neurochemical response to sucrose binges is equivalent to the one observed in response to the abuse of addictive substances like cocaine. The experiments reported here address the effects of sucrose on an invertebrate model, the Platyhelminth brown planarian. The animals exposed to a 10% sucrose solution in one context developed a conditioned place preference (CPP) which was subsequently extinguished in the absence of the rewarding agent. However, one exposure to sucrose per se sufficed to reinstate the CPP response, suggesting sucrose-induced CPP can be characterised as a standard Pavlovian response. The same training procedure led to the development of context-specific tolerance to the effects of sucrose. However, comparing animals treated with dopamine D1 antagonist (SCH-23390) with control animals showed that the establishment of CPP, but not the development of tolerance, is mediated by the dopamine reward system.
Highlights
Following continuous consumption of sweet foods containing sucrose, deprivation can induce in some individuals addictive-like behaviours that lead to increased sweet food intake, a harmful cycle that might contribute to obesity and diabetes (Gearhardt et al 2011)
This experience is likely to result in the development of a second conditioned response which tends to reduce the effects of the drug: the post-intake effects in a naïve individual are opposed by an innate compensatory response that can be controlled by the contextual cues (Remington et al 1997; Siegel 1975)
We developed conditioned place preference (CPP) and tolerance training procedures using an invertebrate model, the Platyhelminth brown planarian, and compared the conditioned responses developed by the animals treated with dopamine D1 antagonist with control animals
Summary
Following continuous consumption of sweet foods containing sucrose, deprivation can induce in some individuals addictive-like behaviours that lead to increased sweet food intake, a harmful cycle that might contribute to obesity and diabetes (Gearhardt et al 2011). Sucrose has been characterised as a substance of abuse in animal models: rats exposed to sucrose display a number of behavioural and physiological responses similar to those elicited by drugs of abuse like cocaine or amphetamine (Avena et al 2008). Those include behavioural changes like conditioned place preference (CPP), withdrawal and craving (Avena et al 2005; Wideman et al 2005), and physiological responses like enhancement of extracellular dopamine in the nucleus accumbens (Bassareo and Di Chiara 1997; Rada et al 2005). If the drug is not available, the animal will experience distress and show symptoms of withdrawal and drug-seeking behaviour
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