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Andrew S. I. Loudon - One of the best experts on this subject based on the ideXlab platform.

  • photoperiodic regulation of leptin resistance in the seasonally breeding siberian hamster phodopus sungorus
    Endocrinology, 2002
    Co-Authors: Karine Rousseau, Zeenat Atcha, Felino R Cagampang, Philippe Le Rouzic, Anne J Stirland, Tina R Ivanov, Francis J P Ebling, Martin Klingenspor, Andrew S. I. Loudon
    Abstract:

    Seasonal Siberian hamsters lose fat reserves, decrease body weight and leptin concentrations, and suppress reproduction on short-day photoperiod (SD). Chronic leptin infusion at physiological doses caused body weight and fat loss in SD animals but was ineffective in long-day (LD) hamsters. Using ovariectomized estrogen-treated females, we tested the hypothesis that responsiveness to leptin is regulated by photoperiod. On SD, hypothalamic neuroPeptide Y, Agouti-Related Peptide, and cocaine- and amphetamine-regulated transcript gene expression in the arcuate nucleus did not exhibit significant changes, and despite SD-induced fat loss, the catabolic Peptide proopiomelanocortin was down-regulated. Food restriction of LD-housed animals caused significant reduction of fat reserves and serum leptin concentrations to SD levels, suppressed serum gonadotropins, and induced increased anabolic (neuroPeptide Y, Agouti-Related Peptide) and decreased catabolic (proopiomelanocortin, cocaine- and amphetamineregulated transcript) gene expression in the arcuate nucleus. Leptin infusion in food-restricted animals had no effect on fat reserves or gonadotropins and did not modulate neuroPeptide gene expression. Also, leptin treatment did not blunt the refeeding responses or weight and fat gain in LD-housed foodrestricted animals. In conclusion, our results strongly suggest that hypothalamic responses to leptin are regulated primarily by photoperiod, rather than seasonal changes in fat reserves, sex steroids, or leptin concentrations. (Endocrinology 143: 3083–3095, 2002)

  • Photoperiodic regulation of leptin resistance in the seasonally breeding Siberian hamster (Phodopus sungorus)
    Endocrinology, 2002
    Co-Authors: Karine Rousseau, Zeenat Atcha, Felino R Cagampang, Philippe Le Rouzic, Tina R Ivanov, Francis J P Ebling, Martin Klingenspor, J. Anne Stirland, Andrew S. I. Loudon
    Abstract:

    Seasonal Siberian hamsters lose fat reserves, decrease body weight and leptin concentrations, and suppress reproduction on short-day photoperiod (SD). Chronic leptin infusion at physiological doses caused body weight and fat loss in SD animals but was ineffective in long-day (LD) hamsters. Using ovariectomized estrogen-treated females, we tested the hypothesis that responsiveness to leptin is regulated by photoperiod. On SD, hypothalamic neuroPeptide Y, Agouti-Related Peptide, and cocaine- and amphetamine-regulated transcript gene expression in the arcuate nucleus did not exhibit significant changes, and despite SD-induced fat loss, the catabolic Peptide proopiomelanocortin was down-regulated. Food restriction of LD-housed animals caused significant reduction of fat reserves and serum leptin concentrations to SD levels, suppressed serum gonadotropins, and induced increased anabolic (neuroPeptide Y, Agouti-Related Peptide) and decreased catabolic (proopiomelanocortin, cocaine- and amphetamine-regulated transcript) gene expression in the arcuate nucleus. Leptin infusion in food-restricted animals had no effect on fat reserves or gonadotropins and did not modulate neuroPeptide gene expression. Also, leptin treatment did not blunt the refeeding responses or weight and fat gain in LD-housed food-restricted animals. In conclusion, our results strongly suggest that hypothalamic responses to leptin are regulated primarily by photoperiod, rather than seasonal changes in fat reserves, sex steroids, or leptin concentrations.

Francis J P Ebling - One of the best experts on this subject based on the ideXlab platform.

  • Short-days induce weight loss in Siberian hamsters despite overexpression of the Agouti-Related Peptide gene.
    Journal of Neuroendocrinology, 2010
    Co-Authors: Preeti H. Jethwa, Roger A.h. Adan, Amy Warner, Maxine J Fowler, Michelle Murphy, M.w.a. De Backer, Perry Barrett, John M. Brameld, Francis J P Ebling
    Abstract:

    Many vertebrates express profound annual cycles of body fattening, although it is not clear whether these represent differential activity of the central pathways known to mediate homeostatic control of food intake and energy expenditure, or whether the recent discovery of a major role for pars tuberalis-ependymal signalling points towards novel mechanisms. We examined this in the Siberian hamster (Phodopus sungorus) by using gene transfection to up-regulate a major orexigenic Peptide, Agouti-Related Peptide (AgRP), and then determined whether this increased anabolic drive could prevent the short-day induced winter catabolic state. Infusions of a recombinant adeno-associated virus encoding an AgRP construct into the hypothalamus of hamsters in the long-day obese phase of their seasonal cycle produced a 20% gain in body weight over 6 weeks compared to hamsters receiving a control reporter construct, reflecting a significant increase in food intake and a significant decrease in energy expenditure. However, all hamsters showed a significant, prolonged decrease in body weight when exposed to short photoperiods, despite the hamsters expressing the AgRP construct maintaining a higher food intake and lower energy expenditure relative to the control hamsters. Visualisation of the green fluorescent protein reporter and analysis of AgRP-immunoreactivity confirmed widespread expression of the construct in the hypothalamus, which was maintained for the 21-week duration of the study. In conclusion, the over-expression of AgRP in the hypothalamus produced a profoundly obese state but did not block the seasonal catabolic response, suggesting a separation of rheostatic mechanisms in seasonality from those maintaining homeostasis of energy metabolism.

  • photoperiodic regulation of leptin resistance in the seasonally breeding siberian hamster phodopus sungorus
    Endocrinology, 2002
    Co-Authors: Karine Rousseau, Zeenat Atcha, Felino R Cagampang, Philippe Le Rouzic, Anne J Stirland, Tina R Ivanov, Francis J P Ebling, Martin Klingenspor, Andrew S. I. Loudon
    Abstract:

    Seasonal Siberian hamsters lose fat reserves, decrease body weight and leptin concentrations, and suppress reproduction on short-day photoperiod (SD). Chronic leptin infusion at physiological doses caused body weight and fat loss in SD animals but was ineffective in long-day (LD) hamsters. Using ovariectomized estrogen-treated females, we tested the hypothesis that responsiveness to leptin is regulated by photoperiod. On SD, hypothalamic neuroPeptide Y, Agouti-Related Peptide, and cocaine- and amphetamine-regulated transcript gene expression in the arcuate nucleus did not exhibit significant changes, and despite SD-induced fat loss, the catabolic Peptide proopiomelanocortin was down-regulated. Food restriction of LD-housed animals caused significant reduction of fat reserves and serum leptin concentrations to SD levels, suppressed serum gonadotropins, and induced increased anabolic (neuroPeptide Y, Agouti-Related Peptide) and decreased catabolic (proopiomelanocortin, cocaine- and amphetamineregulated transcript) gene expression in the arcuate nucleus. Leptin infusion in food-restricted animals had no effect on fat reserves or gonadotropins and did not modulate neuroPeptide gene expression. Also, leptin treatment did not blunt the refeeding responses or weight and fat gain in LD-housed foodrestricted animals. In conclusion, our results strongly suggest that hypothalamic responses to leptin are regulated primarily by photoperiod, rather than seasonal changes in fat reserves, sex steroids, or leptin concentrations. (Endocrinology 143: 3083–3095, 2002)

  • Photoperiodic regulation of leptin resistance in the seasonally breeding Siberian hamster (Phodopus sungorus)
    Endocrinology, 2002
    Co-Authors: Karine Rousseau, Zeenat Atcha, Felino R Cagampang, Philippe Le Rouzic, Tina R Ivanov, Francis J P Ebling, Martin Klingenspor, J. Anne Stirland, Andrew S. I. Loudon
    Abstract:

    Seasonal Siberian hamsters lose fat reserves, decrease body weight and leptin concentrations, and suppress reproduction on short-day photoperiod (SD). Chronic leptin infusion at physiological doses caused body weight and fat loss in SD animals but was ineffective in long-day (LD) hamsters. Using ovariectomized estrogen-treated females, we tested the hypothesis that responsiveness to leptin is regulated by photoperiod. On SD, hypothalamic neuroPeptide Y, Agouti-Related Peptide, and cocaine- and amphetamine-regulated transcript gene expression in the arcuate nucleus did not exhibit significant changes, and despite SD-induced fat loss, the catabolic Peptide proopiomelanocortin was down-regulated. Food restriction of LD-housed animals caused significant reduction of fat reserves and serum leptin concentrations to SD levels, suppressed serum gonadotropins, and induced increased anabolic (neuroPeptide Y, Agouti-Related Peptide) and decreased catabolic (proopiomelanocortin, cocaine- and amphetamine-regulated transcript) gene expression in the arcuate nucleus. Leptin infusion in food-restricted animals had no effect on fat reserves or gonadotropins and did not modulate neuroPeptide gene expression. Also, leptin treatment did not blunt the refeeding responses or weight and fat gain in LD-housed food-restricted animals. In conclusion, our results strongly suggest that hypothalamic responses to leptin are regulated primarily by photoperiod, rather than seasonal changes in fat reserves, sex steroids, or leptin concentrations.

Karine Rousseau - One of the best experts on this subject based on the ideXlab platform.

  • photoperiodic regulation of leptin resistance in the seasonally breeding siberian hamster phodopus sungorus
    Endocrinology, 2002
    Co-Authors: Karine Rousseau, Zeenat Atcha, Felino R Cagampang, Philippe Le Rouzic, Anne J Stirland, Tina R Ivanov, Francis J P Ebling, Martin Klingenspor, Andrew S. I. Loudon
    Abstract:

    Seasonal Siberian hamsters lose fat reserves, decrease body weight and leptin concentrations, and suppress reproduction on short-day photoperiod (SD). Chronic leptin infusion at physiological doses caused body weight and fat loss in SD animals but was ineffective in long-day (LD) hamsters. Using ovariectomized estrogen-treated females, we tested the hypothesis that responsiveness to leptin is regulated by photoperiod. On SD, hypothalamic neuroPeptide Y, Agouti-Related Peptide, and cocaine- and amphetamine-regulated transcript gene expression in the arcuate nucleus did not exhibit significant changes, and despite SD-induced fat loss, the catabolic Peptide proopiomelanocortin was down-regulated. Food restriction of LD-housed animals caused significant reduction of fat reserves and serum leptin concentrations to SD levels, suppressed serum gonadotropins, and induced increased anabolic (neuroPeptide Y, Agouti-Related Peptide) and decreased catabolic (proopiomelanocortin, cocaine- and amphetamineregulated transcript) gene expression in the arcuate nucleus. Leptin infusion in food-restricted animals had no effect on fat reserves or gonadotropins and did not modulate neuroPeptide gene expression. Also, leptin treatment did not blunt the refeeding responses or weight and fat gain in LD-housed foodrestricted animals. In conclusion, our results strongly suggest that hypothalamic responses to leptin are regulated primarily by photoperiod, rather than seasonal changes in fat reserves, sex steroids, or leptin concentrations. (Endocrinology 143: 3083–3095, 2002)

  • Photoperiodic regulation of leptin resistance in the seasonally breeding Siberian hamster (Phodopus sungorus)
    Endocrinology, 2002
    Co-Authors: Karine Rousseau, Zeenat Atcha, Felino R Cagampang, Philippe Le Rouzic, Tina R Ivanov, Francis J P Ebling, Martin Klingenspor, J. Anne Stirland, Andrew S. I. Loudon
    Abstract:

    Seasonal Siberian hamsters lose fat reserves, decrease body weight and leptin concentrations, and suppress reproduction on short-day photoperiod (SD). Chronic leptin infusion at physiological doses caused body weight and fat loss in SD animals but was ineffective in long-day (LD) hamsters. Using ovariectomized estrogen-treated females, we tested the hypothesis that responsiveness to leptin is regulated by photoperiod. On SD, hypothalamic neuroPeptide Y, Agouti-Related Peptide, and cocaine- and amphetamine-regulated transcript gene expression in the arcuate nucleus did not exhibit significant changes, and despite SD-induced fat loss, the catabolic Peptide proopiomelanocortin was down-regulated. Food restriction of LD-housed animals caused significant reduction of fat reserves and serum leptin concentrations to SD levels, suppressed serum gonadotropins, and induced increased anabolic (neuroPeptide Y, Agouti-Related Peptide) and decreased catabolic (proopiomelanocortin, cocaine- and amphetamine-regulated transcript) gene expression in the arcuate nucleus. Leptin infusion in food-restricted animals had no effect on fat reserves or gonadotropins and did not modulate neuroPeptide gene expression. Also, leptin treatment did not blunt the refeeding responses or weight and fat gain in LD-housed food-restricted animals. In conclusion, our results strongly suggest that hypothalamic responses to leptin are regulated primarily by photoperiod, rather than seasonal changes in fat reserves, sex steroids, or leptin concentrations.

Zoe A Archer - One of the best experts on this subject based on the ideXlab platform.

  • hypothalamic neuroPeptide gene expression during recovery from food restriction superimposed on short day photoperiod induced weight loss in the siberian hamster
    American Journal of Physiology-regulatory Integrative and Comparative Physiology, 2007
    Co-Authors: Zoe A Archer, Kimmarie Moar, Tracy Logie, Laura Reilly, Valerie Joan Stevens, Peter J Morgan, Julian G Mercer
    Abstract:

    Previously, 40% food restriction of male Siberian hamsters over 21 days in short-day (SD) photoperiod induced characteristic changes in expression of hypothalamic arcuate nucleus energy balance genes; mRNAs for neuroPeptide Y, Agouti-Related Peptide, and leptin receptor were upregulated, and those of proopiomelanocortin and cocaine- and amphetamine-regulated transcript were depressed. The present study examined the effect of refeeding hamsters for 6 days (∼50% recovery of weight differential) or 19 days (resumption of appropriate weight trajectory). Hyperphagia continued throughout refeeding, but differences in fat pad weights and leptin levels had disappeared after 19 days. Cocaine- and amphetamine-regulated transcript gene expression was depressed by prior restriction in both refed groups. The depressive effect of prior restriction on proopiomelanocortin gene expression had disappeared after 19 days of refeeding. There was no effect of prior food restriction on neuroPeptide Y or Agouti-Related Peptide gene expression. Expression of the anorexigenic brain-derived neurotrophic factor was downregulated in the ventromedial nucleus after SD exposure for 12 wk. In the SD food restriction study, there were effects of photoperiod on brain-derived neurotrophic factor gene expression but not of prior food restriction. Hypothalamic energy balance genes in the hamster respond asynchronously to return to a seasonally appropriate body weight. The achievement of this weight rather than the weight at which caloric restriction was imposed is the critical factor. The differential responses of hypothalamic energy balance genes to food restriction and refeeding are poorly characterized in any species, a critical issue given their potential relevance to human weight loss strategies that involve caloric restriction.

  • hypothalamic gene expression in sheep for cocaine and amphetamine regulated transcript pro opiomelanocortin neuroPeptide y agouti related Peptide and leptin receptor and responses to negative energy balance
    Neuroendocrinology, 2002
    Co-Authors: Clare Lesley Adam, Zoe A Archer, P A Findlay, Louise Thomas, Michel Marie
    Abstract:

    Hypothalamic pathways involved in the regulation of energy balance have not been widely studied in ruminants to date. Here, we used in situ hybridisation to study the gene expression of a number of leptin-sensitive receptors and neuroPeptides in the ovine hypothalamus. Gene expression was first localised for cocaine- and amphetamine-regulated transcript (CART) and Agouti-Related Peptide (AGRP). We then examined in adult male castrated sheep the effects of acute negative energy balance induced by a 4-day fast on the amounts of these mRNAs and those for leptin receptor (OB-Rb), neuroPeptide Y (NPY) and pro-opiomelanocortin (POMC). CART mRNA was localised in the arcuate nucleus (ARC), paraventricular nucleus, median eminence and ventromedial hypothalamic nucleus, and extensive co-localisation with POMC mRNA was demonstrated in the ARC. AGRP mRNA was localised in the ARC. Fasting up-regulated gene expression for OB-Rb and for the orexigenic neuroPeptides NPY and AGRP in the ARC. There was a trend towards down-regulation of gene expression for the anorexigenic neuroPeptide CART and no effect on POMC in the ARC, although these results are inconclusive. The presence or absence of oestradiol-containing subcutaneous implants did not influence gene expression or the effects of fasting. The hypothalamic changes were consistent with responses to the observed reduction in circulation leptin and suggest that the peripheral feedback and central mechanisms for restoring the energy balance may be largely conserved across monogastric and ruminant species.

Julian G Mercer - One of the best experts on this subject based on the ideXlab platform.

  • hypothalamic neuroPeptide gene expression during recovery from food restriction superimposed on short day photoperiod induced weight loss in the siberian hamster
    American Journal of Physiology-regulatory Integrative and Comparative Physiology, 2007
    Co-Authors: Zoe A Archer, Kimmarie Moar, Tracy Logie, Laura Reilly, Valerie Joan Stevens, Peter J Morgan, Julian G Mercer
    Abstract:

    Previously, 40% food restriction of male Siberian hamsters over 21 days in short-day (SD) photoperiod induced characteristic changes in expression of hypothalamic arcuate nucleus energy balance genes; mRNAs for neuroPeptide Y, Agouti-Related Peptide, and leptin receptor were upregulated, and those of proopiomelanocortin and cocaine- and amphetamine-regulated transcript were depressed. The present study examined the effect of refeeding hamsters for 6 days (∼50% recovery of weight differential) or 19 days (resumption of appropriate weight trajectory). Hyperphagia continued throughout refeeding, but differences in fat pad weights and leptin levels had disappeared after 19 days. Cocaine- and amphetamine-regulated transcript gene expression was depressed by prior restriction in both refed groups. The depressive effect of prior restriction on proopiomelanocortin gene expression had disappeared after 19 days of refeeding. There was no effect of prior food restriction on neuroPeptide Y or Agouti-Related Peptide gene expression. Expression of the anorexigenic brain-derived neurotrophic factor was downregulated in the ventromedial nucleus after SD exposure for 12 wk. In the SD food restriction study, there were effects of photoperiod on brain-derived neurotrophic factor gene expression but not of prior food restriction. Hypothalamic energy balance genes in the hamster respond asynchronously to return to a seasonally appropriate body weight. The achievement of this weight rather than the weight at which caloric restriction was imposed is the critical factor. The differential responses of hypothalamic energy balance genes to food restriction and refeeding are poorly characterized in any species, a critical issue given their potential relevance to human weight loss strategies that involve caloric restriction.