Maintaining energy homeostasis

Maintaining energy homeostasis and storing calories when food is available is fundamental for survival. In the modern world, a disruption in energy balance from an increase in calories consumed compared to energy expended is more common than a food scarcity. Unfortunately, over nutrition can lead to obesity, diabetes, nonalcoholic fatty liver disease, colon cancer and many other significant chronic diseases. Clearly, obesity is an increasing public health problem, as now more than two-thirds of the US population is now overweight or obese and parallel occurrences are being seen virtually worldwide
All species have faced the challenge of adapting to scarcity of food and thus strategies to deal with major discrepancies in food availability have evolved to allow propagation of the species. It is clear that the nervous system is the ultimate regulator of these adaptive mechanisms. The central nervous system’s role in regulating energy balance in a coordinated fashion with the constantly adjusting energy intake, expenditure and storage was first demonstrated by early studies in which selective surgical lesions of certain hypothalamic areas was found to result in extreme obesity in rats

Neurons in the hypothalamus including those in the arcuate nucleus are targets of a number of key hormones and metabolic cues. These neurons target several downstream sites to influence complex circuits in the central nervous system (CNS). The downstream effector circuits mediate the coordinated autonomic, behavioral, and endocrine responses to changing levels of metabolic signals. Diminished responses of first order neurons such as those in the arcuate nucleus may contribute to the pathogenesis of obesity and type II diabetes. This includes increased body weight, uncontrolled glycemia, and altered insulin secretion and insulin sensitivity in target tissues such as liver, adipose tissue, pancreas, and skeletal muscle. Thus, the CNS not only regulates food intake and body weight, but also plays a key role in regulating glucose homeostasis in peripheral tissues.

vagus nerve serves as a critical link between changing energy availability and coordinated control of glucose homeostasis The nervous system senses peripheral metabolic cues, resulting in coordinated energy homeostasis.