Comments: Earlier animal studies show a loss of D2 receptors cause by overeating, and human studies show an increase of dopamine D2 receptors when obese patients lose weight. This isn’t settled.
Henry K. Karlsson1, Lauri Tuominen1,2, Jetro J. Tuulari1, Jussi Hirvonen1,3, Riitta Parkkola3, Semi Helin1, Paulina Salminen4, Pirjo Nuutila1,5, and Lauri Nummenmaa1,6
Author contributions: J.H., P.N., and L.N. designed research; H.K.K., L.T., J.J.T., R.P., S.H., P.S., and L.N. performed research; H.K.K., L.T., J.J.T., R.P., and L.N. analyzed data; H.K.K., L.T., J.J.T., J.H., P.N., and L.N. wrote the paper.
- The Journal of Neuroscience, 4 March 2015, 35(9): 3959-3965; doi: 10.1523/JNEUROSCI.4744-14.2015
Abstract
Neurochemical pathways involved in pathological overeating and obesity are poorly understood. Although previous studies have shown increased μ-opioid receptor (MOR) and decreased dopamine D2 receptor (D2R) availability in addictive disorders, the role that these systems play in human obesity still remains unclear. We studied 13 morbidly obese women [mean body mass index (BMI), 42 kg/m2] and 14 nonobese age-matched women, and measured brain MOR and D2R availability using PET with selective radioligands [11C]carfentanil and [11C]raclopride, respectively. We also used quantitative meta-analytic techniques to pool previous evidence on the effects of obesity on altered D2R availability.
Morbidly obese subjects had significantly lower MOR availability than control subjects in brain regions relevant for reward processing, including ventral striatum, insula, and thalamus.
Moreover, in these areas, BMI correlated negatively with MOR availability. Striatal MOR availability was also negatively associated with self-reported food addiction and restrained eating patterns.
There were no significant differences in D2R availability between obese and nonobese subjects in any brain region. Meta-analysis confirmed that current evidence for altered D2R availability in obesity is only modest. Obesity appears to have unique neurobiological underpinnings in the reward circuit, whereby it is more similar to opioid addiction than to other addictive disorders.
The opioid system modulates motivation and reward processing, and low μ-opioid availability may promote overeating to compensate decreased hedonic responses in this system. Behavioral and pharmacological strategies for recovering opioidergic function might thus be critical to curb the obesity epidemic.
ARTICLE
Obesity associated with brain’s neurotransmitters
March 4th, 2015 in Neuroscience /
Obesity is associated with lowered opioid receptor availability (top row) whereas availability of dopamine receptors remains unchanged. Brains in the left column belong to obese people and brains in the right column to normal-weight people. Credit: Aalto University
Researchers at Aalto University and University of Turku have revealed how obesity is associated with altered opioid neurotransmission in the brain.
New research reveals how obesity is associated with altered functioning of brain’s opioid system, which is intimately involved in generating pleasurable sensations. Researchers found that obesity was associated with significantly lowered number of opioid receptors in the brain. However, no changes were observed in the dopamine neurotransmitter system, which regulates motivational aspects of eating.
Obesity is a great challenge to human health worldwide because it is associated with serious medical conditions such as type 2 diabetes, coronary heart disease, and stroke. Even though it is well known that unhealthy eating habits are the major cause for obesity, people have often problems with restraining their eating.
Our findings highlight how obesity is associated with brain-level molecular changes. It is possible that the lack of brain’s opioid receptors predisposes the obese individuals to overeating to compensate decreased hedonic responses in this system, tell professor Lauri Nummenmaa and researcher Henry Karlsson.
The findings have major implications for our understanding of the causes of obesity. They help us to understand the mechanisms involved in overeating, and provide new insight into behavioural and pharmacological treatment and prevention of obesity. However, we do not yet know whether the altered brain neurochemistry is a cause or consequence of obesity.
The researchers measured availability of mu-opioid and type 2 dopamine receptors in normal-weight and obese individuals‘ brains using positron emission tomography at the Turku PET Centre.
The findings were published on March 3, 2015 in the scientific journal The Journal of Neuroscience.
Provided by Aalto University
“Obesity associated with brain’s neurotransmitters.” March 4th, 2015. http://medicalxpress.com/news/2015-03-obesity-brain-neurotransmitters.html
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