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Dr Julian Mercer

Research Interests

Obesity is the result of an imbalance between energy intake and energy expenditure in favour of the former. Understanding of the physiological systems that are involved in the regulation of food intake and energy balance has advanced considerably in the last decade, but it is still uncertain why these systems fail to maintain a stable body weight and composition, allowing obesity to develop. Knowledge of the factors contributing to the development of overweight and obesity will be important as we attempt to counter the onward march of the global obesity epidemic. Two animal models are being studied. The Siberian hamster is a seasonal mammal that displays cycles in body weight in response to changes in daylength that mimic environmental conditions encountered in the wild. The mechanisms that underlie the ability of these animals to adjust their body weight and body fatness, and to do this voluntarily despite the provision of food in excess, could be of fundamental importance. Most common human obesity is not the result of mutations or polymorphisms in a single gene, but rather represents the interaction of genetic susceptibility (multiple genes) with environment, where diet is an influential component. We are characterising a rat model of diet-induced obesity, with particular emphasis on responses to different obesogenic diets, including readily-ingested liquid diets. Both animal models are being studied mechanistically at the level of the brain signalling pathways that regulate energy balance, and the feedback of peripheral hormones and metabolites onto these pathways. The ability of reward systems to interact with and override energy homeostasis systems is an area of growing interest.

Highlighted Publications

Helwig M, Khorooshi RM, Tups A, Barrett P, Archer ZA, Exner C, Rozman J, Braulke LJ, Mercer JG, Klingenspor M. PC1/3 and PC2 Gene Expression and Post-Translational Endoproteolytic Pro-Opiomelanocortin Processing is Regulated by Photoperiod in the Seasonal Siberian Hamster (Phodopus sungorus). J Neuroendocrinol. 2006 Jun;18(6):413-25.

Tups A, Helwig M, Stohr S, Barrett P, Mercer JG, Klingenspor M. Photoperiodic regulation of insulin receptor mRNA and intracellular insulin signaling in the arcuate nucleus of the Siberian hamster, Phodopus sungorus. Am J Physiol Regul Integr Comp Physiol. 2006 Apr 6; [Epub ahead of print]

Beck B, Kozak R, Moar KM, Mercer JG. Hypothalamic orexigenic peptides are overexpressed in young Long-Evans rats after early life exposure to fat-rich diets.
Biochem Biophys Res Commun. 2006 Apr 7;342(2):452-8. Epub 2006 Feb 9.

Tups A, Barrett P, Ross AW, Morgan PJ, Klingenspor M, Mercer JG. The suppressor of cytokine signalling 3, SOCS3, may be one critical modulator of seasonal body weight changes in the Siberian hamster, Phodopus sungorus. J Neuroendocrinol. 2006 Feb;18(2):139-45.

Mercer JG, Archer ZA. Diet-induced obesity in the Sprague-Dawley rat: dietary manipulations and their effect on hypothalamic neuropeptide energy balance systems. Biochem Soc Trans. 2005 Nov;33(Pt 5):1068-72.