Ph.D. Physiological Psychology University of Florida 1981
Obesity is a disease of figuratively and literally large proportions. Changes in body weight, reflected as changes in body fat, are realized through alterations in energy intake and /or energy expenditure. A wide range of animal species, including humans, can exhibit impressive seasonal increases and decreases in body weight and fat. We have been examining the naturally occurring changes in body weight and fat, as well as associated seasonal changes in reproduction, in several hamster species. In these species we have found that the photoperiod (day-length) controls these and other seasonal responses. Siberian hamsters (Phodopus sungorus sungorus) decrease their body weight when exposed to short (winter-like) days; these decreases are reflected solely as decreases in body fat. We have demonstrated that the changes in the photoperiod are transduced into a neuroendocrine signal that triggers these seasonal responses based on the duration of secretion of the pineal gland hormone, melatonin. We have demonstrated the critical nature of the durational signal by giving daily programmed infusions of melatonin to freely moving, pinealectomized Siberian hamsters.
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