Actions of orexin in the regulation of energy balance metabolism

Orexin, also known as hypocretin, is a neuropeptide which is expressed by the neurons in the lateral hypothalamic area. The orexinergic nerve fiber terminals project widely in the brain and its receptors also widely distribute in the brain. The signal of orexin involves the integration of many physiological processes, such as arousal, feeding, spontaneous activity, reward seeking, as well as function control of autonomic nerve. Orexinergic nerve participates in the energy metabolism of the body through the regulation of multiple physiological activities. Based on the research progress on physiological functions of orexin and regulations of orexin neuron excitation, we have analyzed and explored the regulatory role of the orexin nerve in the balance of energy metabolism. Orexin is regulated by blood glucose, ghrelin and leptin. The decrease of blood glucose or the increase of ghrelin when an individual is hungry or decreases of leptin in an emaciation patient can all enhance excitability of orexin neurons, so as to promote awakening, activities and motivation of ingestion. Meanwhile, orexin makes the individual prepare for gaining food by increasing blood pressure, heart rate and the use of glucoses through sympathetic nerves. It can also make the digestive system ready for digesting food by promoting gastric acid secretion and gastric motion through vagus nerves. After feeding, following the increase of blood glucose and accumulation of adenosine which occurs while energy is consumed during activities, the excitability of orexin neurons decreases and the secretions of orexin reduces, leading to low desire, less movement and sleep of the individual, so as to save and store energy. Thus, orexinergic system has integrated a mechanism for the individual to intake and apply energy, and is maintaining the necessary balance of energy metabolism for life activities.