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Photoperiodic Changes in Endocannabinoid Levels and Energetic Responses to Altered Signalling at CB1 Receptors in Siberian Hamsters

Authors

  • J. M. Ho,

    1. Department of Biology, Indiana University, Bloomington, IN, USA.
    2. Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, IN, USA.
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  • N. S. Smith,

    1. Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, IN, USA.
    2. Department of Biology, Xavier University of Louisiana, New Orleans, LA, USA.
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  • S. A. Adams,

    1. Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, IN, USA.
    2. Program in Neuroscience, Indiana University, Bloomington, IN, USA.
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  • H. B. Bradshaw,

    1. Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, IN, USA.
    2. Program in Neuroscience, Indiana University, Bloomington, IN, USA.
    3. Department of Psychological Brain Sciences, Indiana University, Bloomington, IN, USA.
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  • G. E. Demas

    1. Department of Biology, Indiana University, Bloomington, IN, USA.
    2. Center for the Integrative Study of Animal Behavior, Indiana University, Bloomington, IN, USA.
    3. Program in Neuroscience, Indiana University, Bloomington, IN, USA.
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Jacqueline M. Ho, Department of Medicine Division of Metabolism, Endocrinology, and Nutrition, University of Washington; Veterans Affairs Puget Sound Health Care System, Seattle, WA 98108, USA (email: jmh529@uw.edu)

Abstract

Siberian hamsters (Phodopus sungorus) adapt to seasonal environmental conditions with marked changes in body mass, primarily in the form of adiposity. Winter-like conditions (e.g. short days) are sufficient to decrease body mass by approximately 30% in part via reductions in food intake. The neuroendocrine mechanisms responsible for these changes are not well understood, and homeostatic orexigenic/anorexigenic systems of the hypothalamus provide little explanation. We investigated the potential role of endocannabinoids, which are known modulators of appetite and metabolism, in mediating seasonal changes in energy balance. Specifically, we housed hamsters in long or short days for 0, 3, or 9 weeks and measured endocannabinoid levels in the hypothalamus, brainstem, liver and retroperitoneal white adipose tissue (RWAT). An additional group of males housed in short days for 25 weeks were also compared with long-day controls. Following 9 weeks in short days, levels of the endocannabinoid 2-arachidonoylglycerol (2-AG) were significantly elevated in RWAT and reduced in brainstem, although they returned to long-day levels by week 25 in short-day males that had cycled back to summer-like energy balance. Endocannabinoid levels in these tissues correlated significantly with adiposity and change in body mass. No photoperiodic changes were observed in the hypothalamus or liver; however, sex differences in 2-AG levels were found in the liver (males > females). We further tested the effects of CB1 receptor signalling on ingestive behaviour. Five daily injections of CB1 antagonist SR141716 significantly reduced food intake and body mass but not food hoarding. Although the CB1 agonist arachidonyl-2-chloroethylamide did not appreciably affect either ingestive behaviour, body mass was significantly elevated following 2 days of injections. Taken altogether, these findings demonstrate that endocannabinoid levels vary with sex and photoperiod in a site-specific manner, and that altered signalling at CB1 receptors affects energy balance in Siberian hamsters.

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