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Title: The role of the hypothalamic-pituitary-growth axis in the regulation of seasonal and exercise induced weight gain in the Siberian hamster
Author: Dumbell, Rebecca
ISNI:       0000 0004 5348 7182
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2014
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The Siberian hamster (Phodopus sungorus) undergoes a suite of physiological changes in response to short day (SD) photoperiod which includes a marked reduction in body mass (up to 40%). This altered physiology can be reversed by a return to long day (LD) photoperiod and is driven by changes hypothalamic gene expression. Additionally, stimulation of weight regain occurs through spontaneous exercise when hamsters are provided with a running wheel (RW), despite intact photoperiod appropriate hypothalamic gene expression. The foundation hypothesis for this investigation was that the change in body weight in both paradigms is underpinned by an alteration of the growth hormone (GH) axis. Pasireotide, a somatostatin agonist, was utilised to inhibit GH secretion from the pituitary in both paradigms. Measurement of body mass, mass of internal organs, body composition by magnetic resonance imaging, hormonal analysis and in situ hybridization were used to determine the effect of a blockade of GH secretion by pasireotide. Pasireotide suppressed the GH axis in Siberian hamsters; with reduced circulating insulin-like growth factor-1 and altered hypothalamic gene expression of somatostatin (srif) and growth hormone – releasing hormone (ghrh) consistent with an inhibition of pituitary GH secretion. Pasireotide treatment inhibited RW and LD stimulated growth, and when administered to LD hamsters caused weight loss in a similar manner to that which occurs in SD and accompanied by testicular atrophy. In addition, pasireotide increased the incidence of torpor and increased bout length of this hypometabolic state in sedentary SD hamsters. In conclusion, evidence is provided for the hypothalamic – pituitary – growth hormone axis in the determination of photoperiod and RW induced body weight changes. Furthermore, the data show evidence for a novel muscle – brain pathway and evidence for a neuroendocrine pathway involved in torpor induction.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Laboratory animals ; Hypothalamic-pituitary-adrenal axis