Oct 27, 2015 04:35 PM By Susan Scutti
Insulin regulates the release of dopamine, a neurotransmitter in the brain’s reward and pleasure centers: study. Thomas Abbs, CC by 2.0
Insulin is a hormone that controls blood sugar levels and helps you feel full after eating. A new animal study reveals a previously unknown role for insulin: regulating the release of dopamine, a neurotransmitter in the brain’s reward and pleasure centers.
“Our results imply that insulin can serve as a reward signal, in addition to its established role in signaling satiety,” concluded the NYU Langone Medical Center researchers.
When there’s more insulin in the brain, the researchers say, more dopamine will be released, thus increasing the sense of pleasure. For those who love to eat, this study may help explain the irresistible quality of high-carb foods. They not only provide a “sugar” rush, but quite possibly a “reward” rush, as well.
Dopamine is a neurotransmitter, which is a chemical necessary for communication between neurons in the brain, a Psychology Today article explains. In a word, dopamine makes us want. Present in brain regions involved in emotion, motivation, pleasure, and movement, it sends signals through our brain’s reward system in response to natural behaviors linked to survival, including sex and eating. While it is known that some foods, such as proteins, cause a moderate release of dopamine, other foods, such as sugars, will cause the neurotransmitter to spike.
The new study, then, set out to explore how insulin might influence this process. And so Dr. Margaret Rice and Dr. Kenneth Carr, co-principal investigators, and a team of researchers conducted a series of experiments on rodents.
In one experiment, Rice, a neuroscientist, and Carr, a psychiatrist, and their colleagues recorded a 20 percent to 55 percent increase in dopamine released in the striatal region of the rodent brain. This rise occurred during the same time-frame insulin activity increased. Importantly, given a choice between a drink that triggered insulin signals (and led to more dopamine) or one that did not, the rats consistently chose the drink that offered a dopamine rush.
In another set of experiments, the research team discovered rats fed low-calorie diets had a 10-times greater sensitivity to rising insulin levels in their brains than rats fed a normal diet. Only a tenth, then, of the insulin levels necessary to a rat eating a normal diet could spur a dopamine release. By contrast, the rats fed a high-calorie diet had lost their responsiveness to insulin.
All told, the experiments suggest a previously unseen role for insulin as part of the brain’s reward system. The experiments also indicated the brains of improperly fed rodents eventually failed to respond in a natural manner to food and the insulin it triggers. Presumably, over time these rodents no longer felt rewarded.
Naturally, the same might be true of people. Chronically-elevated insulin levels and lowered insulin sensitivity in the brain are closely tied to obesity, the researchers said. The dopamine rush (or lack of one) may be the reason so many of us are overeating, essentially trying our best to regain that high.
Source: Stouffer MA, Woods CA, Patel JC, et al. Insulin enhances striatal dopamine release by activating cholinergic interneurons and thereby signals reward. Nature Communications. 2015.