Writing in the journal of Biological Psychiatry, the researchers discuss their work in identifying a group of serotonin neurons that are connected to and activate dopamine neurons.
The researchers, led by Dr Yong Xu, associate professor of pediatrics at Baylor and senior author of the paper, specifically identified the serotonin 2C receptor and its precise role in suppressing binge eating.
Binge-eating is the practice of consuming large amounts of food in a short time frame, and can form the basis of other eating disorders such as bulimia.
The scale of binge-eating
A report commissioned by the UK eating disorder charity Beat, found that more than 725,000 people in the UK are affected by an eating disorder.
The National Institute of Health and Clinical Excellence estimates around 11% of those affected by an eating disorder are male.
Impaired brain 5-hydroxytryptamine (5-HT; serotonin) signalling has been put forward as a strong candidate in the onset of binge eating in humans.
Binge eating patients are found to have increased brain 5-HT uptake and consequently decreased 5-HT content.
The study took mice and randomly assigned them into intermittent high-fat diet (HFD), continuous chow/HFD or continuous chow only groups.
Intermittent mice were first exposed to both regular chow pellets (6.5% fat) and a HFD pellets (40% fat) for 48 hours and then exposed to only chow for the rest of the week.
Weekly cycles were then repeated, with both HFD and chow criteria for 24 hours and only chow for the rest of the week.
On the binge assessment day (Mondays of each cycle), HFD and chow intake was measured for 2.5 hours.
The continuous chow/HFD group was exposed to both chow and HFD for the entire study, and both HFD and chow intake was measured for 2.5 hours at the same time as intermittent group.
The other control group, continuous chow only, was exposed to this diet for the entire study. Chow intake was measured 2.5 hours at the same time as the intermittent group.
The 2.5-hour HFD intake in intermittent mice was used to assess binge-like eating behaviour in response to various drugs, gene mutations, and their combinations.
“Human literature suggests that dysfunction of the serotonin system or dopamine system in the brain may be associated with developing binge-like eating behaviour," said Xu.
"However, mechanistically, there's no direct evidence to show how this system affects behaviour."
Previous animal studies
The central dopamine system has previously been identified in the progression of binge eating. Rats that binge on sucrose have shown increased dopamine release in the brain. Stimulation of a brain region connected to this condition has inhibited binge eating in mice.
These studies, along with this study’s results, suggest a potential role of dopamine neurons in the pathophysiology and treatment of binge eating.
“Our data supports a model in which 5-HT stimulates dopamine neural activity through a 5-HT2CR-mediated mechanism,” the study concludes.
“Activation of this midbrain 5-HT to the dopamine neural circuit effectively inhibits binge-like eating behavior in mice. The 5-HT2CR population in dopamine neurons could be one potential target for antibinge therapies.”
Source: Biological Psychiatry
Published online ahead of print, DOI: 10.1016/j.biopsych.2016.06.005
“Activation of Serotonin 2C Receptors in Dopamine Neurons Inhibits Binge-like Eating in Mice.”
Authors: Yong Xu et al.