The Siberian hamster and Fischer 344 (F344) rat exhibit strong natural alterations in body weight that are programmed by the ambient photoperiod and allow preparation for the approaching season, whereby they have a lower body weight in winter-like photoperiods (8 h light per day). The mechanisms that permit this dynamic regulation of body weight may identify novel targets for anti-obesity drugs. Siberian hamster studies involved analysis of photoperiod-driven gene expression changes in the hypothalamic paraventricular nucleus using tissue obtained by laser capture microdissection. Juvenile F344 rats were susceptible to diet-induced obesity and defended a photoperiod-sensitive rate of lean mass deposition. In addition, mRNA levels of various genes were found to be photoperiodically regulated in the mediobasal hypothalamus (MBH) including traditional energy balance genes and growth-related genes (e.g. neuropeptide Y and growth hormone releasing hormone). Furthermore, a time course study using Affymetrix arrays was used to analyse the changes in gene expression following 3 d, 14 d and 28 d of exposure to long or short photoperiod in the MBH. Dramatic changes in gene expression in the thyroid hormone system were found at all time points and confirmed by <i>in situ</i> hybridisation. The changes found correlated with recent findings in the quail and sheep documenting thyrotropin release from the pituitary regulating thyroid hormone levels in the MBH. These studies also identified strong photoperiodic regulation of two novel systems related to the thyroid hormone axis; the retinoid and Wnt signalling pathways. Thus, these studies establish the F344 rat as an interesting seasonal animal model and further understanding of the underlying mechanisms of photoperiodism.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:521353 |
| Date | January 2009 |
| Creators | Reilly, Laura |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=114455 |
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