title: Steady-state energy balance in animal models of obesity and weight loss.
abstract: OBJECTIVE
  We wanted to exam the steady-state energy balance by using high-fat diet-induced obese (DIO) rats and mice as models for positive energy balance, and gastric bypassed (GB) rats and gene knockout of muscarinic acetylcholine M3 receptor (M3KO) mice as models for negative energy balance.
  
  
  METHODS
  One hundred and thirty-two rats and mice were used. Energy balance was measured by a comprehensive laboratory animal monitoring system. Gene expression was analysed by in situ hybridisation in M3KO mice.
  
  
  RESULTS
  DIO rats reached the plateau of body weight 28 weeks after starting high-fat diet (25% heavier than controls), whereas DIO mice reached the plateau after 6 weeks (23% heavier than controls). At the plateau, DIO rats had higher calorie intake during the light phase but not during the dark phase, while mice had the same calorie intake per day as controls. DIO rats and mice had lower energy expenditure (EE) and respiratory exchange ratio (RER) than controls. GB-rats reached the plateau (15% weight loss) 2 weeks after surgery and had the same calorie intake as sham-operated controls. EE, but not RER, was higher in GB rats than controls during the dark phase. The lean M3KO mice (25% lighter than wild-type (WT) mice at the plateau between 6 and 15 months of age) had the same calorie intake but higher EE, RER and hypothalamic mRNA expression of NPY, AgRP and leptin receptor than WT mice.
  
  
  CONCLUSIONS
  When body weight gain or loss reached a plateau, the steady-state energy balance was mainly maintained by EE and/or RER rather than calorie intake.
authors.affiliation: a Department of Cancer Research and Molecular Medicine , Norwegian University of Science and Technology , Trondheim , Norway.
authors.forename: Magnus Kringstad
authors.initials: MK
authors.lastname: Olsen
authors.affiliation: a Department of Cancer Research and Molecular Medicine , Norwegian University of Science and Technology , Trondheim , Norway.
authors.forename: Helene
authors.initials: H
authors.lastname: Johannessen
authors.affiliation: b The Rowett Institute, University of Aberdeen , Aberdeen , Scotland.
authors.forename: Nikki
authors.initials: N
authors.lastname: Cassie
authors.affiliation: b The Rowett Institute, University of Aberdeen , Aberdeen , Scotland.
authors.forename: Perry
authors.initials: P
authors.lastname: Barrett
authors.affiliation: c Department of Pharmacology and Experimental Therapeutics , Kyoto Pharmaceutical University , Kyoto , Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Takeuchi
authors.affiliation: a Department of Cancer Research and Molecular Medicine , Norwegian University of Science and Technology , Trondheim , Norway.|d Department of Surgery , Centre for Obesity Research and Innovation, St. Olav's University Hospital , Trondheim , Norway.
authors.forename: Bård
authors.initials: B
authors.lastname: Kulseng
authors.affiliation: a Department of Cancer Research and Molecular Medicine , Norwegian University of Science and Technology , Trondheim , Norway.|d Department of Surgery , Centre for Obesity Research and Innovation, St. Olav's University Hospital , Trondheim , Norway.
authors.forename: Duan
authors.initials: D
authors.lastname: Chen
authors.affiliation: a Department of Cancer Research and Molecular Medicine , Norwegian University of Science and Technology , Trondheim , Norway.
authors.forename: Chun-Mei
authors.initials: CM
authors.lastname: Zhao
mesh_terms: D000818:Animals; D001921:Brain / Q000473:pathology; D004041:Dietary Fats; D004195:Disease Models, Animal; D004734:Energy Metabolism; D005260:Female; D015390:Gastric Bypass; D017403:In Situ Hybridization; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008820:Mice, Obese; D009765:Obesity / Q000378:metabolism* / Q000601:surgery*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D043587:Receptor, Muscarinic M3 / Q000235:genetics; D015431:Weight Loss
chemical_list: D004041:Dietary Fats; D012333:RNA, Messenger; D043587:Receptor, Muscarinic M3
keywords: Eating behaviour; gastric bypass; high-fat diet; mice; muscarinic acetylcholine M3 receptor knockout; rats