Obesity is a pandemic syndrome frequently associated with the most prevalent pathologies in developed countries, including diabetes, atherosclerosis, ischemic episodes, and cancer (1). Obesity results from an imbalance in the complex system of peripheral and intrahypothalamic pathways controlling appetite regulation and energy homeostasis (2). The hypothalamic control of energy homeostasis involves interaction between food intake stimulating neurons (orexigenic), expressing neuropeptide Y/agouti-related protein (NPY/AGRP), and food intake inhibiting neurons (anorexigenic), expressing pro-opiomelanocortin/cocaine and amphetamine-regulated transcript (POMC/CART) (3,4). Peripheral signals have been shown to modulate the activity of NPY/AGRP and POMC neurons within key appetite regulating nuclei of the hypothalamus, such as the arcuate. These circulating factors include the well-known orexigenic peptide ghrelin, released from the oxyntic cells in the stomach, and the anorexigenic hormones insulin and leptin, released by the pancreas and the fat tissue (5,6). Despite the accumulated knowledge on neuropeptide signaling in the hypothalamus (2,3), little information is available on the integrated mechanism of neuronal activation during appetite regulation and how this circumstance could affect the neuroglial metabolic coupling mechanisms underlying neurotransmission events. On these grounds, methods providing further insight into hypothalamic metabolism and its disturbances entail considerable interest to improve our understanding, prognosis, and therapy of energy homeostasis and food intake disorders.In vivo and in vitro 1 H and 13 C NMR approaches have been successful in providing a wealth of information on cerebral metabolism and neuroglial interactions during sensory or motor activation (7-10). However, the relatively large voxel sizes involved in the acquisition of in vivo NMR spectra preclude its use in studying the relatively small hypothalamic area, particularly in small rodents. Similarly, the relatively large amounts of cerebral tissue needed to prepare brain extracts for high-resolution 13 C NMR constitute an important limitation for regional studies of hypothalamic processes. Recently, high-resolution magic angle spinning (HR-MAS) spectroscopy has been proposed as a convenient alternative (11). In this technique, the removal of dipolar couplings at the magic angle (54.7°) permits the acquisition of high-resolution spectra from small tissue samples, with similar quality to that only previously achievable via solution spectroscopy. In most cases, 1 H HR-MAS has been used for metabolic profiling of normal and diseased tissues (11), whereas 13 C HR-MAS offers the additional advantage of providing information on the operation of cerebral metabolic pathways and neuroglial coupling mechanisms, under similar conditions to high-resolution 13 C NMR spectroscopy (12) but using smaller tissue biopsies and without the need of solvent extraction. This makes it possible to investigate the oxida-

BackgroundCombatting over-weight or obesity can lead to large fluctuations in an individual’s body weight, often referred to as weight cycling or “yo-yo” dieting. Current evidence regarding the potentially damaging effects of these changes is conflicting.MethodsHere, we assess the metabolic effects of weight cycling in a murine model, comprising three dietary switches to normal or high fat diets at 6 week intervals; male C57BL/6 mice were fed either a control (C) or high fat (F) diet for 6 weeks (n=140/group). C and F groups were then either maintained on their initial diet (CC and FF respectively) or switched to a high fat (CF) or control (FC) diet (n=35/group). For the final 6 week interval, CC and CF groups were returned to the control diet (CCC and CFC groups) while FC and FF groups were placed on a high fat diet (FCF and FFF) (n=28/group).ResultsFor the majority of metabolic outcomes changes aligned with dietary switches; however assessment of neuropeptides and receptors involved in appetite regulation and reward signalling pathways reveal variable patterns of expression. Furthermore, we demonstrate that multiple cycling events leads to a significant increase in internal fat deposition, even when compared to animals maintained on a high fat diet (Internal Fat: FCF: 7.4 ± 0.2g vs. FFF: 5.6 ± 0.2g; p<0.01).ConclusionsIncreased internal adipose tissue is strongly linked to the development of metabolic syndrome associated conditions such as type 2 diabetes, cardiovascular disease and hypertension. While further work will be required to elucidate the mechanisms underlying the neuronal control of energy homeostasis, these studies provide a causative link between weight cycling and adverse health.