Towards an Understanding of Physiological Body Mass Regulation: Seasonal Animal Models

Area of Science:

• Physiology
• Neuroendocrinology
• Obesity Research

Background:

• Mammalian body mass is regulated by conserved mechanisms, potentially involving distinct neurochemical substrates for long-term defense versus short-term energy homeostasis.
• An "appropriate" body mass is hypothesized to be encoded in the brain, influencing nutritional and reproductive physiology.

Purpose of the Study:

• To explore hypotheses regarding mammalian body mass regulation and its relevance to human obesity and weight-loss resistance.
• To highlight the utility of seasonal rodent models, specifically the Siberian hamster, for investigating body mass regulation mechanisms.

Main Methods:

• Review of existing hypotheses on body mass regulation.
• Examination of seasonal rodent models, focusing on the Siberian hamster's photoperiodic responses.
• Analysis of the role of photoperiod and melatonin in adjusting and defending body mass.

Main Results:

• Siberian hamsters demonstrate continuous, progressive body mass adjustment based on photoperiodic history, achieving a seasonally appropriate body mass.
• These adjustments are retained even after food restriction, indicating a memorized set-point.
• Photoperiod, via melatonin, can physiologically reset the defended body mass level.

Conclusions:

• Seasonal mammals provide a unique model for understanding fundamental body mass regulation mechanisms.
• Photoperiod manipulation offers a non-invasive method to study body mass control systems.
• Insights from seasonal models may reveal generic principles applicable to energy homeostasis and obesity treatment.