Dopamine Release by Sucrose

Preferred foods are often used as prototypes of natural rewards. Preferred tastes reduce the sensory complexity of foods to a single sensory modality to simplify the model further. The central neural areas most often associated with both natural and drug-induced rewards are included in the mesoaccumbens dopamine system. What follows summarizes research on the relationship between ingesting sucrose solutions and activity in this system. After introducing the concepts and difficulties encountered in studying the neural basis of reward, we discuss our own research documenting the short- and long-term effects that licking sucrose has on dopamine release in the nucleus accumbens. During sucrose intake, dopamine is released in the nucleus accumbens as a function of concentration. The effect occurs in both naive and experienced animals, but does not require stimulation or absorption in the gastrointestinal tract. Conversely, increasing the availability of dopamine in the accumbens also stimulates sucrose ingestion. The thalamocortical taste system has little influence on sucrose elicited dopamine release, but severing the direct pontine gustatory connections with the limbic system reduces the effect substantially. Scheduled, daily access to a sucrose solution also produces longer-term effects by altering accumbens dopamine reuptake and receptor mechanisms. Despite the correlation between oral sucrose stimulation and accumbens dopamine, this model of biological reward is influenced by a variety of other neurotransmitters and hormones. Some of these affects may operate via the dopamine system as well, that is, they could mediate the effects of sucrose in the accumbens, but many influence gustatory neural processing directly, even at the level of the taste bud. Thus, the mesoaccumbens dopamine system provides a useful model for studying central reward mechanisms but, at least for gustatory stimuli, other levels including the periphery must be evaluated as well.