LAUSR

It is well known that exercise in itself has several benefits in terms of health and fitness [1, 2], as well as neural and cognitive effects [3], in both humans and laboratory animals. Food restriction and regular exercise are the two major established strategies for the prevention and treatment of obesity, which is currently recognized as a serious burden worldwide. However, obesity is often associated with physical inactivity and disrupted life rhythms, including binge and night eating [4], which makes the treatment of obesity more complicated and weight reduction less attainable. Although exercise is recommended for the purpose of weight reduction through the increment of energy expenditure, it is generally difficult for most obese subjects to continue regular exercise for long periods of time. Thus, it is important to explore the putative mechanisms for producing the motivation to perform and adhere to exercise, especially in obese subjects. Ghrelin, originally identified as a growth hormone secretagogue (GHS), is an orexigenic gut hormone. It is a 28-amino-acid peptide produced by the X/A-like endocrine cells in the oxyntic glands of the gastric fundus [5, 6]. Ghrelin functions primarily as an orexigen [7] and as a GH-releasing hormone [5]. Various other physiologic roles have been reported, including modulation of energy metabolism [8] and regulation of the autonomic nervous system [9, 10] and cardiovascular system [11]. In contrast to a significant decrease after a single bout of exercise [12], the long-term outcomes of periodic exercise on the ghrelin dynamics are still controversial and have not been clarified. Here we demonstrate beneficial effects of long-term voluntary exercise on disrupted rhythms of daily activity, which are often observed in obese subjects, in relation to the amelioration of extraordinary ghrelin production in an obese model. Furthermore, because ghrelin is relevant to higher motivation and hyperactivity [13, 14], it is plausible that ghrelin plays an essential role in the formation of motivation and in the adherence to exercise.