Effects of photoperiod and gonadectomy on food intake, body weight, and body composition in Siberian hamsters

Abstract

Two experiments examined the effects of gonadectomy, photoperiod, and melatonin treatment on food intake, body weight, and carcass composition in male and female Siberian hamsters (Phodopus sungorus sungorus). Gonadectomy caused small decreases in body weight in both sexes but did not affect food intake. In males the weight reduction was due to small (nonsignificant) decreases in all carcass components. Ovariectomy caused a significant reduction in carcass lipid but did not affect lean body mass. A short photoperiod (8 h light, 16 h dark, LD 8:6) caused significant weight losses in all animals except ovariectomized females. Daily melatonin injections (12.5 micrograms sc, 3 h before lights-out) also reduced body weight in males and females housed in a long photoperiod (LD 16:8). The photoperiod- and melatonin-induced weight losses were almost entirely due to decreases in carcass lipid; lean body mass was unaffected by either treatment. Although short photoperiods and melatonin treatments decreased food intake, these changes were preceded by a significant loss of body weight. Thus photoperiod induced changes in food intake may be a consequence of the changes in body weight, rather than vice versa. These findings indicate that photoperiod and melatonin have important effects on adipose tissue mass in both Siberian and Syrian hamsters, even though one species gains weight (Syrian) and the other loses weight (Siberian) in short photoperiods.

Neural control of white, beige and brown adipocytes

“…Finally, although well after these seminal studies reporting brite/beige adipocytes in traditionally WAT depots 2002 (ref 22) , but before the most recent flurry of brite/ beige cell 'rediscovery', we found that Siberian hamsters (Phodopus sungorus) transferred from long 'summer-like' photoperiods (light:dark 16:8 h) to short 'winter-like' photoperiods (light: dark 8:16 h) in the laboratory with typical vivarium ambient temperature (~22-23°C) had increased WAT β 3 -adrenoceptor and UCP-1 gene expressions in retroperitoneal WAT (the only WAT pad tested for these responses 22 ). These data showed for the first time, to our knowledge, that a naturally occurring reversal of an obese state (~50% body fat to~20% body fat 23 ) that induces increases in the sympathetic drive to WAT 24 also triggers browning, doing so without decreases in ambient temperature. 22 Collectively, the finding of brownish (brite/beige) adipocytes in WAT depots that were thought to be the province of only white adipocytes, has a 30-year history, but despite this, only recently has this been recognized as a common phenomenon across many mammalian species including humans.…”

Body mass affects seasonal variation in sickness intensity in a seasonally-breeding rodent

“…Body mass was recorded every other day for this group, and food access was adjusted so that the LD-FR group mean body mass tracked the SD-AL group mean. We modulated food availability to the LD-FR group to target the pattern of body mass loss in the SD-AL group, rather than providing food quantities that were pair matched to SD-AL food intake, because body mass loss in short days is influenced by other factors in addition to food intake (Wade and Bartness, 1984).…”

Thematic review series: Adipocyte Biology. Sympathetic and sensory innervation of white adipose tissue

“…When Siberian hamsters are exposed to long days (LDs), they develop a severe obesity [?50% body fat (17)(18)(19)], a level as extreme as that seen in genetically inbred strains of rats and mice [e.g., ob/ob mice (20) and Zucker fa/fa rats (21)]. The LD-induced obesity of Siberian hamsters is completely reversible by exposure to short days (SDs), with the decrease in body fat being most rapid during the first 5-6 weeks of SDs (17,18,(22)(23)(24).…”

“…The LD-induced obesity of Siberian hamsters is completely reversible by exposure to short days (SDs), with the decrease in body fat being most rapid during the first 5-6 weeks of SDs (17,18,(22)(23)(24). Moreover, the body fat loss during this time occurs without a concomitant decrease in food intake but eventually (.6 weeks of SD exposure) is accompanied by an ?30% decrease in food intake (17,25,26); thus, the initial body fat loss is attributable to increased energy expenditure.…”

“…The LD-induced obesity of Siberian hamsters is completely reversible by exposure to short days (SDs), with the decrease in body fat being most rapid during the first 5-6 weeks of SDs (17,18,(22)(23)(24). Moreover, the body fat loss during this time occurs without a concomitant decrease in food intake but eventually (.6 weeks of SD exposure) is accompanied by an ?30% decrease in food intake (17,25,26); thus, the initial body fat loss is attributable to increased energy expenditure. Unlike other photoperiod-induced obesity models (27), the SD-induced decrease in WAT is nonuniform, with the more internally located visceral fat pads mobilizing their lipid stores first and to a greater extent than the more externally located subcutaneous fat pads (18,28,29).…”