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Urge to Overeat Linked to Production of Natural Narcotic

Last Updated: September 21, 2012.

When presented with tasty foods, the brain produces the opioid peptide enkephalin that stimulates an unexpected reward center in the brain and leads to overeating, according to a study published online Sept. 20 in Current Biology.

FRIDAY, Sept. 21 (HealthDay News) -- When presented with tasty foods, the brain produces the opioid peptide enkephalin that stimulates an unexpected reward center in the brain and leads to overeating, according to a study published online Sept. 20 in Current Biology.

Noting that mu-opioid receptors are abundant in the dorsal neostriatum, which has been implicated in reward-related functions as well as movement, Alexandra G. DiFeliceantonio, from the University of Michigan in Ann Arbor, and colleagues measured extracellular levels of endogenous striatal opioid peptides by placing probes in the anteromedial dorsal neostriatum of rats before and after they were presented with large quantities of M&M chocolate candies.

The researchers found that levels of enkephalin surged by >150 percent as the rats ate the chocolates. Injecting a mu receptor agonist directly into the same area of the brain increased the intake of sweet foods by >250 percent, without affecting the rats liking for sweetness. The rats ate the equivalent of a 68 kg human consuming about 3.6 kg of M&Ms in an hour. Fos plume mapping confirmed that the effect was mediated through the anteromedial quadrant of the dorsal neostriatum and not diffusion of mu receptor agonists to other areas.

"In conclusion, our results provide novel evidence that enkephalin surges and mu-opioid stimulation in the same anteromedial dorsal neostriatum region contribute to signaling the opportunity to eat a sensory reward and to causally generating increased consumption of that reward," DiFeliceantonio and colleagues write.

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