In vivo ghrelin release from the arcuate nucleus measured by push-pull perfusion

E. Ali, C. Cayer, M. Wellman, A. Abizaid, J. S. James, Z. Merali

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Ghrelin is a stomach-derived neuropeptide involved in appetite, food intake and energy balance through the interaction of its receptor, growth hormone secretagogue receptor, which are widely distributed in the brain. Total ghrelin is represented as, the active form, n-octanoyl-modified ghrelin, and its inactive counterpart, des-acyl ghrelin. Ghrelin is mainly synthesized in the stomach however both types have been discovered in the arcuate nucleus (ARC) of the hypothalamus in rats and mice at low levels. Previous research has indicated that ghrelin neurons in the hypothalamus project to orexigenic neurons and anorexigenic neurons, each with competing effects on feeding. The ARC plays a crucial role in the regulation of food intake and energy homeostasis and its relationship with ghrelin makes it a key target for metabolic conditions such as obesity. However, the local release of ghrelin at the ARC and whether it is the main source of ghrelin in the central nervous system has never been elucidated. The objective of the present study is to assess the local release of ghrelin at the ARC using in vivo push-pull perfusion. Sprague Dawley rats (n=8) were anesthetized and implanted with push-pull perfusion probes aiming at the ARC. Artificial cerebrospinal fluid (aCSF) was perfused at a flow rate of 6 ╬╝l/min. After the collection of three baseline samples (collected every 20 minutes), potassium (145mM) was added to the perfusion medium, and another six samples were then collected. Radioimmunoassay analysis revealed that the addition of potassium to the aCSF elicited an immediate and robust (80%) increase in total local ghrelin release at the ARC. These results constitute the first measurement of in vivo central ghrelin release which will hopefully provide future insight into the role of brain endogenous ghrelin in appetite and energy balance.