Orexin and metabolism

Abstract

Orexin has been confirmed to exhibit acute orexigenic effects, especially for palatable food. However, the loss of orexin renders mice susceptible to obesity, which suggests that orexin neurons function as a negative regulator of energy metabolism over an extended period of time. Thus, orexin exerts differential short-term and long-term effects on feeding behavior and energy metabolism. Orexin neurons are able to sense nutritional and energy status directly or indirectly through leptin, glucose, amino acids and other factors. Orexin neurons project to various brain regions from the forebrain to the spinal cord, which are involved in food intake, reward behavior and sympathetic nervous system activity; orexin's effects in these regions modulate food salience and energy expenditure. Orexin has also been reported to be involved in glucose and bone metabolism. Surprisingly, very little is currently known regarding the roles of the two orexin receptors and especially regarding the long-term effects on metabolism. The local action of orexin in the peripheral organs remains controversial.