Early 2013 worldwide obesity had nearly doubled since 1980; over half a billion adults and 40 million pre-school children were obese. Shockingly, overweight and obesity nowadays kill more people worldwide than malnutrition does (WHO, 2013). This Q3 huge threat to human health has provided an impetus to the research on body weight regulation and energy homeostasis. Energy homeo- stasis requires an accurate match between energy intake, i.e. food intake and digestion, and energy expenditure, i.e. basal metabolic rate, physical activity and thermogenesis for endotherms. A key hormone coordinating this balance is the almost two decades ago discovered hormone leptin, named after the Greek root leptoz meaning lean (Zhang et al., 1994). In mammals, leptin is produced by, and circulates in proportion to the amount of the white adipose tissue and acts in the hypothalamus on two primary types of neurons in the arcuate nucleus. One set of neurons is inhibited by leptin and expresses the orexigenic neuropeptide Y and agouti- related peptide (NPY/AgRP) (Broberger et al., 1998), whereas the other is stimulated by leptin and expresses the anorexigenic pro- opiomelanocortin (in fact the POMC-derived a-melanophore stimulating hormone, a-MSH) and cocaine and amphetamine
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