The Effects of Sucrose on Neuronal Activity (pp. 75-114)
Authors: (Elena Timofeeva and Arojit Mitra, Faculté de Médecine, Département Psychiatrie et Neurosciences, Centre de Recherche de l’Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec (QC), Canada)
Abstract: During the past few centuries humans have transformed from rear to voracious consumers of sugar. The present chapter sheds light on the questions of why we did increased our sugar consumption and what effects sucrose intake can produce on our mood and mind. Once consumed, sucrose sends signals to the brain via specialized taste receptors and glucosensing mechanisms. Sucrose intake activates in the brain the primary gustatory pathway and the brain reward system, which recognizes sweet taste of sucrose as rewarding. The role of the sweet taste system is to detect potentially high-energy sweet food that normally is relatively rare in the nature. The glucosensing mechanisms stimulate or inhibit food intake according to the energy needs. Because of the scarcity of sweet food in the nature, seeking this type of food requires some effort. Therefore, once such a food is found and consumed, this effort would be awarded by the brain reward system. These sophisticated systems work properly when their functions are not compromised by the unlimited availability of sweet palatable food, which may counteract the precise mechanisms controlling food intake. The experimental results obtained in animal models have shown that seeking and consumption of the regular non-sweet foods activate the medial hypothalamus which is directly related to the control of energy homeostasis and stress response. In contrast, seeking and consumption of sucrose inhibit the activity of the medial hypothalamus, but strongly activate the brain reward areas. This sucrose-induced shift in neuronal activity results in consumption of more and more palatable sweet foods at the expense of regular low-energy foods. Repeated overeating of sucrose can alter the neurochemical state of the brain reward regions, promoting sucrose craving and triggering sucrose binge-eating episodes. On the other hand, a sucrose-induced decrease in the activity of the medial hypothalamus directly affects the response of neuroendocrine system to stress. The stress-induced neuronal expression of stress neuropeptides as well as the release of plasma stress hormones is blunted by sucrose consumption. This ‘anti-stress’ effect of sucrose may explain overconsumption of sweets during stress even in the absence of hunger or needs for calories. This chapter reviews the neuronal effects of sucrose that from one side is beneficial by giving us energy and helping to relieve stress, or, from the other side, it may be detrimental by leading to uncontrolled craving for sucrose, eating disorders and obesity.
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