Abstract
Obesity causes a significant negative impact on health of human beings world-wide. The main reason for weight gain, which eventually leads to obesity, is excessive ingestion of energy above the body’s homeostatic needs. Therefore, the elucidation of detailed mechanisms for appetite control is necessary to prevent and treat obesity. N-methyl-d-aspartate (NMDA) receptor is a post-synaptic glutamate receptor and is important for excitatory neurotransmission. It is expressed throughout the nervous system, and is important for long-term potentiation. It requires both ligand (glutamate) and co-agonist (d-serine or glycine) for efficient opening of the channel to allow calcium influx. d-serine is contained in fermented foods and marine invertebrates, and brain d-serine level is maintained by synthesis in vivo and supply from food and gut microbiota. Although the NMDA receptor has been reported to take part in the central regulation of appetite, the role of d-serine had not been addressed. We recently reported that exogenous d-serine administration can suppress appetite and alter food preference. In this review, we will discuss how NMDA receptor and its co-agonist d-seine participate in the control of appetite and food preference, and elaborate on how this system could possibly be manipulated to suppress obesity.
Highlights
Obesity causes a significant negative impact on health of human beings world-wide
Dietary risk factors and physical inactivity, which are two risk factors contributing to the development of obesity, collectively accounted for 10% of global death and disability-adjusted life years (DALYs; sum of years lived with disability and years of life lost) in 2010 [2]
In the Global Burden of Disease Study 2013, 13 among 25 leading global risk factors for DALYs were related to either diet or symptoms of metabolic syndromes, and high BMI itself ranked as the third [3]
Summary
Obesity has become a major health issue on a global scale. Based on the WHO’s definition of obesity (BMI > 30 kg/m2), more than 600 million adults were obese and more than 1.9 billion adults were overweight (BMI 25–30 kg/m2) in 2014 [1]. In the Global Burden of Disease Study 2013, 13 among 25 leading global risk factors for DALYs were related to either diet or symptoms of metabolic syndromes, and high BMI itself ranked as the third [3] These global indices draw enough attention, the real impact of obesity is still underestimated, because the obesity risk on disease susceptibility is different among ethnic backgrounds. The ingestion of palatable food releases dopamine in the striatum in proportion to the ratings of meal pleasantness and activates reward circuitry [15,16]. Homeostatic orexigenic signals increase the activity of VTA dopaminergic neurons when exposed to food stimuli, whereas anorexigenic signals inhibit firing of dopaminergic neurons and decrease dopamine release [22]. Overconsumption of rewarding food can lead to changes in the reward circuitry [31], causing less activation of the circuits by the palatable food in obese subjects [32]. Blunted activation of the dopamine system by consumption of rewarding food could trigger overconsumption to compensate for the blunted response of the reward circuit [33]
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