Published online Oct 15, 2014. doi: 10.4239/wjd.v5.i5.606
Revised: May 15, 2014
Accepted: May 31, 2014
Published online: October 15, 2014
Processing time: 252 Days and 13.5 Hours
A re-examination of the mechanism controlling eating, locomotion, and metabolism prompts formulation of a new explanatory model containing five features: a coordinating joint role of the (1) autonomic nervous system (ANS); (2) the suprachiasmatic (SCN) master clock in counterbalancing parasympathetic digestive and absorptive functions and feeding with sympathetic locomotor and thermogenic energy expenditure within a circadian framework; (3) interaction of the ANS/SCN command with brain substrates of reward encompassing dopaminergic projections to ventral striatum and limbic and cortical forebrain. These drive the nonhomeostatic feeding and locomotor motivated behaviors in interaction with circulating ghrelin and lateral hypothalamic neurons signaling through melanin concentrating hormone and orexin-hypocretin peptides; (4) counterregulation of insulin by leptin of both gastric and adipose tissue origin through: potentiation by leptin of cholecystokinin-mediated satiation, inhibition of insulin secretion, suppression of insulin lipogenesis by leptin lipolysis, and modulation of peripheral tissue and brain sensitivity to insulin action. Thus weight-loss induced hypoleptimia raises insulin sensitivity and promotes its parasympathetic anabolic actions while obesity-induced hyperleptinemia supresses insulin lipogenic action; and (5) inhibition by leptin of bone mineral accrual suggesting that leptin may contribute to the maintenance of stability of skeletal, lean-body, as well as adipose tissue masses.
Core tip: The novel proposal for the mechanism of body weight regulation deals with all three components of body mass: bone, lean tissue, and fat depots. It attributes the central control of counterbalancing energy expenditure and intake to an autonomic nervous system-circadian clock command center that encompases brain reward substrates, lateral hypothalamic peptidergic circuits and areas of the cortex. The nonhomeostatic character of feeding and locomotion is driven and controlled by the reward circuits and modulated by shifts in insulin sensitivity induced by counterregulation by leptin of insulin as weight deviates between underweight and overweight and alters basal leptin concentrations.