Research Description:
Untitled Document
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.
Long day ('summer-like'; left) and short day ('winter-like'; right) Siberian hamsters (Phodopus sungorus) showing seasonal, photoperiod-triggered responses in body mass and pelage color
One goal of our research program is to study the mechanisms underlying the
melatonin-induced changes in body fat in Siberian hamsters. This goal is being
accomplished through the use of in vivo endocrine/neuroendocrine depletion-repletion
paradigms, and through in vitro incubation of isolated adipocytes (fat cells)
treated with putative mediators of the melanin-induced lipid metabolic responses.
We also are investigating the regulation of seasonally appropriate total body
fat content using surgical fat pad removal (lipectomy). In addition, using antero-
and retrograde tract tracing techniques and neurotransmitter turn-over measurement,
we are continuing to explore our finding that adipocytes are innervated by the
sympathetic nervous system (see photograph below). We also are identifying the
brain structures that are involved in the reception/interpretation of the melatonin
signal by either using selective lesion techniques (e.g., microknife cuts) to
disrupt the putative melatonin signal receotion system or by stimulating these
sites with microinfusions of the hormone. Finally, we are studying the acquisition
of food (foraging) and its storage (food hoarding) in a seminatural environment.
The goal of these studies is to determine the neural and hormonal mechanisms
underlying this naturally occurring behavior including the effects of pregnancy
and lactation, as well as neuropeptides traditionally tested for their effects
on food intake in other species.
Collectively, these experiments should prove useful in understanding the neural
and hormonal control of energy balance and their consequences for understanding
pathological conditions of energy balance such as obesity. In addition, we should
gain a better understanding of basic fat cell metabolism and the general abilities
of animals to make anticipatory adaptive responses that enhance their survival
and reproduction.
Double-label fluorescence immunohistochemistry of the hypothalamic paraventricular nucleus showing dual sympathetic nervous system innervation (yellow) of white fat (green) and brown fat (red) using two transneuronal viral tract tracers (two genetically-engineered strains of the pseudorabies virus [PRV]).
The sympathetic nervous system innervates white adipose tissue where it is involved in the mobilization of stored lipid fuels (lipolysis) and innervates brown adipose tissue where it is involved in increasing thermogenesis (generating heat). In some situations, such as cold exposure, both white and brown adipose tissue are stimulated such that needed energy if mobilized from white adipose tissue and brown adipose tissues generates heat.
Recent Publications:
Goldman, B. D., Song, C. K. and Bartness, T. J. Seasonal Rhythms: Seasonal hormonal changes and behavior. In Larry R. Squire, Editor-in-Chief, Encyclopedia of Neuroscience, Academic Press, Oxford, 2008., in press.
Festuccia, W. T., Oztezcan, S., Laplante, M., Berthiaume, M., Michel, C., Dohgu, S., Denis, R. G., Brito, M. N., Brito, N. A., Miller, D. S., Banks, W. A., Bartness, T. J., Richard, D. and Deshaies, Y. PPAR?-mediated positive energy balance in the rat is associated with reduced sympathetic drive to adipose tissues and thyroid status. Endocrinology, 149:2121-2130, 2008.
Leitner, C. and Bartness, T. J. Food deprivation-Induced changes in body fat mobilization after neonatal monosodium glutamate treatment, American Journal of Physiology, 294:R775-783, 2008.
Dailey, M. E. and Bartness, T. J. Fat pad-specific effects of lipectomy on foraging, food hoarding and food intake. American Journal of Physiology, 294:R321-328, 2008.
Bartness, T. J. and Song, C. K. Brain-adipose tissue neural crosstalk. Physiology and Behavior, 91:343-351, 2007.
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